Phantom drive?
Paul Förster
... I have a strange problem I never encountered before. With my C64C,
I do LOAD"$",8 and it says SEARCHING FOR $, though no drive is
connected. It sees a phantom drive though the DEVICE NOT PRESENT error
should occur -- and does with other C64s.
I already checked CIA2, U21, U22 and U23 and replaced them with known
good parts. The symptom remains.
I don't need to mention that the C64C doesn't access a connected drive
anymore (it used to work)... I've checked with known good drives and
they are good for other C64Cs. So the drive is definitily not the
culprit. I also checked Ray Carlsen's infos and the schematics (which
brought me to U21-U23) but I'm stuck here.
Any ideas? Some resistor, capacitor or something?
--
cul8er
Paul Förster
On 2009-11-05 12:04:46 +0100, Paul F�rster <paul.f...@gmx.net> said:
> I already checked CIA2, U21, U22 and U23 and replaced them with known
> good parts. The symptom remains.
... oops! That was meant to be CIA2, U21, U22 and U3, not U23. Sorry.
--
cul8er
Ruud
> ... oops! That was meant to be CIA2, U21, U22 and U3, not U23. Sorry.
This error normally occurs when the 7406 and/or 74LS14 inside a 1541
are broken and short circuit the Data and/or Clock line. But with no
1541 attached, it cannot be them. IMHO the same can happen in the C64.
So please check the 7406 inside your C64.
But knowing you have been soldering, check with an Ohm meter if you
haven't unwantedly shortcircuit someting with a drop of solder.
--
___
/ __|__
/ / |_/ Groetjes, Ruud
\ \__|_\
\___| URL: Ruud.C64.org
Paul Förster
On 2009-11-05 13:11:47 +0100, Ruud <Ruud.Ba...@apg.nl> said:
> This error normally occurs when the 7406 and/or 74LS14 inside a 1541
> are broken and short circuit the Data and/or Clock line. But with no
> 1541 attached, it cannot be them. IMHO the same can happen in the C64.
> So please check the 7406 inside your C64.
>
> But knowing you have been soldering, check with an Ohm meter if you
> haven't unwantedly shortcircuit someting with a drop of solder.
... I already checked a couple of times. And I've tried three different
7406 chips, to no avail. That's why I ask.
--
cul8er
Paul Förster
On 2009-11-05 13:11:47 +0100, Ruud <Ruud.Ba...@apg.nl> said:
> But knowing you have been soldering, check with an Ohm meter if you
> haven't unwantedly shortcircuit someting with a drop of solder.
... ok, I've double checked *again*, all 14 pins of the chip. All of
them connect where they are supposed to connect. There are no soldering
drops or shorts of neighboring lines. All *seems* well, but something
gotta be wrong here.
--
cul8er
Martin 'Martinland' Schemitsch
> Hi,
> On 2009-11-05 12:04:46 +0100, Paul Fï¿œrster <paul.f...@gmx.net> said:
>> I already checked CIA2, U21, U22 and U23 and replaced them with known
>> good parts. The symptom remains.
> ... oops! That was meant to be CIA2, U21, U22 and U3, not U23. Sorry.
What about U2, they make good music too!
OK, I tried, sorry... ;)
ML
--
----------------------------------------------------------
"I don't know. I'm making this up as I go!"
(Ford as Dr. Jones Jr. in 'Raiders of the Lost Ark')
----------------------------------------------------------
Paul Förster
On 2009-11-05 22:47:37 +0100, "Martin 'Martinland' Schemitsch"
<team8ma...@hotmail.com> said:
> What about U2, they make good music too!
> OK, I tried, sorry... ;)
... that's a matter of taste. But CIA2 sits in position U2. So
unfortunately, it doesn't help me.
--
cul8er
Ruud
> ... I already checked a couple of times. And I've tried three different
> 7406 chips, to no avail. That's why I ask.
I meant that you have to check if there is a short circuit between
Data and Ground and/or Clock and Ground. Preferably with no 7406 in
the socket.
Just an idea: what you can do is insert CIA2 but leave out all pins
involved with the IEC bus. IMHO in this way the C64 should act as if
there is no drive connected.
--
___
/ __|__
/ / |_/ Groetjes, Ruud
\ \__|_\
\___| http://Ruud.C64.org
Paul Förster
On 2009-11-06 13:22:22 +0100, Ruud <Ruud.Ba...@apg.nl> said:
> I meant that you have to check if there is a short circuit between
> Data and Ground and/or Clock and Ground. Preferably with no 7406 in
> the socket.
... I tried without the 7406. If I do that, the screen stays blank when
powering on...
I'll cross-check the lines again. Maybe I missed something.
> Just an idea: what you can do is insert CIA2 but leave out all pins
> involved with the IEC bus. IMHO in this way the C64 should act as if
> there is no drive connected.
... according to the schematics, that would be pins 5 (ATN OUT), 6 (CLK
OUT), 7 (DATA OUT) and 9 (DATA) of CIA2, right? Pin 8 (CLK) has a
connection to pin 4 of U22, but what would happen to the CIA if it was
inserted without a clock signal? Would that damage the CIA?
Also, pin 24 (FLAG) of CIA1 is connected to the serial port. But the
latter goes to CASS RD (D, 4) on the cassette port too and cassette
works fine. So I wouldn't suspect the problem there.
And there are definitely no shorts between each of the serial bus
connections. I checked all possible combinations.
Ok, I'll prepare a socket for the CIA2 test. I don't want to bend the
CIA chip's pins. CIAs are too precious chips. Also, I try them in
sequence and not all at once. That'd give me more information about
which one might be the culprit.
I'll keep you posted. Thanks very much for helping. :-) I hope I can
locate the problem.
--
cul8er
Paul Förster
... ok, here's an update:
On 2009-11-06 13:22:22 +0100, Ruud <Ruud.Ba...@apg.nl> said:
> I meant that you have to check if there is a short circuit between
> Data and Ground and/or Clock and Ground. Preferably with no 7406 in
> the socket.
... oh, this is strange. The C64 wouldn't show a picture without the
7406 previously. Now it does. Don't aks me why... You made me curious
to give it another shot and so I removed the 7406 again and now the C64
properly powers on.
I've cross-checked all combinations, not just neighboring lines of the
serial connector and the 7406 socket each. There are no other shorts
than pin 1 and pin 5 of the 7406, which according to the schematics is
correct.
Anyway, having removed the 7406 and powered on the C64, it correctly
shows DEVICE NOT PRESENT. So my guess is the chip is bad. But that
wouldn't explain why 6 brand new chips fresh from the factory don't
work.
BUT: I have ordered a brand new load of 7406 chips and tried 6 of them.
All with the same result. I cannot imagine that 60% of the brand new
load should be defective...
The old chip reads:
7406N
FDY5150
8741VJ
The new chips read:
84H5RCK E4 <- the "E4" is small printed and underlined
SN7406N
The former (old) chip has a big "S" printed in front of it. Is that the
manufacturer? And if so, what is it? The new chips are made by TI. They
bear the Texas Instruments logo.
Is there any difference between these chips? Have I tried the wrong chips?
Maybe I try and desolder the one of the dead board you gave me (which I
have butchered halfway anyway ;-) and try that chip...
--
cul8er
Paul Förster
On 2009-11-06 13:22:22 +0100, Ruud <Ruud.Ba...@apg.nl> said:
> I meant that you have to check if there is a short circuit between
> Data and Ground and/or Clock and Ground. Preferably with no 7406 in
> the socket.
> Just an idea: what you can do is insert CIA2 but leave out all pins
> involved with the IEC bus. IMHO in this way the C64 should act as if
> there is no drive connected.
... ok, here are my findings:
I put CIA2 in a socket and bent pins 5, 6, 7, 8 and 9 one after the
other. But I only bent one pin at a time so that all other pins were
connected.
The result was good when each of the pins 5, 6, 8 and 9 were bent away.
Only with pin 7 bent away the symptom remained. To me this means it
could be any one of these four pins in combination with pin 7. Still, I
can't find no short. :-(
I decided to analyze U3 too and found some very strange things indeed:
1. I can't find pins 1, 2 and 3 of U3 anywhere in the schematic.
2. By checking your dead board I found by accident that U3 pin 1 is
short with U2 pin 1. I cross checked with my board and they are open.
If I short them as with your dead board, I get a high beep sound and no
picture. I power off, remove the connection and all is well. Very
strange...
3. According to schematics, U3 pin 4 should go to U7 pin 13 and U8 pin
38. While it is connected correctly to U8 pin 38, it is connected to U7
pin 16 instead of 13. This is the same with your board.
Are there bugs in the schematics?
--
cul8er
Webster
> ... oh, this is strange. The C64 wouldn't show a picture without the
> 7406 previously. Now it does. Don't aks me why... You made me curious to
> give it another shot and so I removed the 7406 again and now the C64
> properly powers on.
>
> I've cross-checked all combinations, not just neighboring lines of the
> serial connector and the 7406 socket each. There are no other shorts
> than pin 1 and pin 5 of the 7406, which according to the schematics is
> correct.
>
> Anyway, having removed the 7406 and powered on the C64, it correctly
> shows DEVICE NOT PRESENT. So my guess is the chip is bad. But that
> wouldn't explain why 6 brand new chips fresh from the factory don't work.
>
My EPROM programmer will test 7406 Logic, if you want to know if it's
bad send me an email (remove DELETE)and I will give you my address.
Garberstreet Electronics
"Webster" <timwm...@pgtc.com> wrote in message news:gpidnZqRd_R392nX...@pgtc.com...
I'm not a big Commodore guy, but a chip is a chip, and I'd suspect
that there is a short preventing the 7406 from functioning properly,
or it is blowing the chip as soon as it is powered up. At least he
has narrowed this down to a single location. Now to find what it is
that's causing it.
Bill Garber of Garberstreet Electronics
http://www.garberstreet.com
Paul Förster
On 2009-11-06 19:34:29 +0100, Webster <timwm...@pgtc.com> said:
> My EPROM programmer will test 7406 Logic, if you want to know if it's
> bad send me an email (remove DELETE)and I will give you my address.
... thanks very much for the offer. But sending ten chips to you just
for testing would be a bit overkill. You are in England, right? I live
in Switzerland. Buying ten new chips takes only a day and not two weeks
and is ten times as cheap. :-) Still, thanks very much.
--
cul8er
Paul Förster
On 2009-11-06 19:33:16 +0100, "Garberstreet Electronics"
<will...@comcast.net> said:
> I'm not a big Commodore guy, but a chip is a chip, and I'd suspect
> that there is a short preventing the 7406 from functioning properly,
> or it is blowing the chip as soon as it is powered up. At least he
> has narrowed this down to a single location. Now to find what it is
> that's causing it.
... well, I think, with Ruud's tip about the CIA -> serial port pin
test, I can narrow the problem even to the pins 3, 4, 8, 9, 12 or 13 of
U22 because these pins would be the ones affected when bending the CIA
pins away. Funny enough, the DEVICE NOT PRESENT message appears
correctly if I bend *any* of the pins 5, 6, 7 or 9 of the CIA away.
Still, the remark about blowing the 7406 when powering up is very
important. Let's just hope that this is not the case.
--
cul8er
Peter Schepers
Paul F�rster <paul.f...@gmx.net> wrote:
>Hi Bill,
>
>On 2009-11-06 19:33:16 +0100, "Garberstreet Electronics"
><will...@comcast.net> said:
>> I'm not a big Commodore guy, but a chip is a chip, and I'd suspect
>> that there is a short preventing the 7406 from functioning properly,
>> or it is blowing the chip as soon as it is powered up. At least he
>> has narrowed this down to a single location. Now to find what it is
>> that's causing it.
>
>... well, I think, with Ruud's tip about the CIA -> serial port pin
>test, I can narrow the problem even to the pins 3, 4, 8, 9, 12 or 13 of
>U22 because these pins would be the ones affected when bending the CIA
>pins away. Funny enough, the DEVICE NOT PRESENT message appears
>correctly if I bend *any* of the pins 5, 6, 7 or 9 of the CIA away.
I vaguely remember dealing with one C64 that had a serial port issue. I
found that one or more of the traces between the serial port and the 7406
were bad, either shorted together or to something else. I believe I ended
up x-acto'ing the existing traces out and running jumpers between the port
and the 7406.
The only way I found out what was wrong was by making sure each pin on the
7406 had the correct voltage, and was pinned directly to the serial port
and the 6522. All the data lines are being pulled up by 1K pull-up
resistors, and one connects directly to the 6522.
>Still, the remark about blowing the 7406 when powering up is very
>important. Let's just hope that this is not the case.
TTL chips (74xx series) are very hardy. Their pins can take shorts to both
GND and Vcc. It's only Vcc over-voltages that can hurt, but that would be
affecting most of the chips in the machine.
PS.
Paul Förster
On 2009-11-07 22:43:39 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
> I vaguely remember dealing with one C64 that had a serial port issue. I
> found that one or more of the traces between the serial port and the 7406
> were bad, either shorted together or to something else. I believe I ended
> up x-acto'ing the existing traces out and running jumpers between the port
> and the 7406.
>
> The only way I found out what was wrong was by making sure each pin on the
> 7406 had the correct voltage, and was pinned directly to the serial port
> and the 6522. All the data lines are being pulled up by 1K pull-up
> resistors, and one connects directly to the 6522.
... I was thinking about something along that line. I had the idea
tonight when I realized how simple it should be according to the
schematics. I was thinking about putting a 7406 on a small board along
with 1K resistors (RP6) and the diodes CR9..17, wire that to CIA2,
while disconnecting its pins 5-9 from the board and wiring them to the
new extra chip and try again. If that works, then the fault is beyond
the CIA. If it does not work, then the CIA itself might be an issue,
tho I've alreay tried 3 different CIA chips.
I could try that without having to bend CIA pins. The CIA sits in a
socket so I can make an adaptor for it and not have to manipulate it
physically -- and possibly damage it by breaking pins or something like
this.
What do you mean by correct voltages? It should be max. 5V in that
whole area of the board. I have no oscilloscope so I can't analyze it
in detail. I have a standard multimeter that can do resistence,
voltage, capacity, amps, transistors, tubes and some other stuff. Would
that be enough to check the voltages on the individual pins? I thought,
since signals change so fast there is no way to measure the voltages
other than Vcc and GND with a standard multimeter... hey, my
electronics knowledge is still *BASIC* but it's growing slowly. :-)
> TTL chips (74xx series) are very hardy. Their pins can take shorts to both
> GND and Vcc. It's only Vcc over-voltages that can hurt, but that would be
> affecting most of the chips in the machine.
... that's good news. So maybe the chips are not fried after all. They
definitely shouldn't have to stand over-voltages because where in the
whole system should be anywhere over the max. 12V (a little more to be
precise) that comes from the 12V DC input power supply...?
Yesterday, I also had the strange effect again that taking out the 7406
for checking purposes would not give me a picture *once* when powering
on again. So I suspect a slack joint at the 4066 (U21) because they are
next to each other and I touched it when removing the 7406. Strange
enough, the picture immediately came back when powering it on the next
time. Maybe U21 has a slack joint (too)? I'll check that... In any
event, a slack joint on U21 shouldn't affect operation of U22 because
they have nothing to do with each other according to schematics.
Please allow me a dumb question: In the schematics the small boxes
representing the inverter gates of U22 have a "1" printed inside them.
What does that mean?
--
cul8er
Paul Förster
On 2009-11-05 12:04:46 +0100, Paul F�rster <paul.f...@gmx.net> said:
> Any ideas? Some resistor, capacitor or something?
... I was just curious and checked RP6, the 1k Ohm SIL resistor array.
I found that pins 4 and 6 show a resistive value of about 670 Ohm while
pins 2, 3 and 5 showed the proper value of 1k Ohm. I compared that to a
good board where all 5 pins show a value of 1k Ohm. I wonder if my
serial problem could be due to a bad RP6 resistor. If so, would one of
the following do?
http://tinyurl.com/y8nfdea
http://tinyurl.com/y892bz3
The schematic says, all resistors are 1/4 Watts +/- 5%. Propably the
second (yellow) because of the Watts? I didn't find any 0.25W or
greater SIL 6-pin resistor at their site (the only useful site in
Switzerland), so would 0.2W do?
--
cul8er
Paul Förster
On 2009-11-08 15:52:33 +0100, Paul F�rster <paul.f...@gmx.net> said:
> ... I was just curious and checked RP6, the 1k Ohm SIL resistor array.
... hmm, it's not RP6. I've exchanged that with a definitely good one
(tested before soldering in) from another board. It now shows the same
odd behavior on pins 4 and 6. And the old one which I have soldered out
shows proper 1k Ohm on *all* pins. It's interesting that a resistor
changes its value when soldered in. Or that'd mean there is some
parallel resistance which is lower (~670 Ohm)...
--
cul8er
Peter Schepers
>
>On 2009-11-07 22:43:39 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
>
>> I vaguely remember dealing with one C64 that had a serial port issue. I
>> found that one or more of the traces between the serial port and the 7406
>> were bad, either shorted together or to something else. I believe I ended
>> up x-acto'ing the existing traces out and running jumpers between the port
>> and the 7406.
>>
>> The only way I found out what was wrong was by making sure each pin on the
>> 7406 had the correct voltage, and was pinned directly to the serial port
>> and the 6522. All the data lines are being pulled up by 1K pull-up
>> resistors, and one connects directly to the 6522.
>
>... I was thinking about something along that line. I had the idea
>tonight when I realized how simple it should be according to the
>schematics. I was thinking about putting a 7406 on a small board along
>with 1K resistors (RP6) and the diodes CR9..17, wire that to CIA2,
>while disconnecting its pins 5-9 from the board and wiring them to the
>new extra chip and try again. If that works, then the fault is beyond
>the CIA. If it does not work, then the CIA itself might be an issue,
>tho I've alreay tried 3 different CIA chips.
It's a bit of work what you're proposing. You will need to wire the
outputs from the 7406 to a serial port as well. You can eliminate the
diodes from your test, though.
Thinking about the diodes... have you checked all of them? They are there
for over/undervoltage spikes. It's easy to verify they are OK with the
diode checker on your multimeter.
>I could try that without having to bend CIA pins. The CIA sits in a
>socket so I can make an adaptor for it and not have to manipulate it
>physically -- and possibly damage it by breaking pins or something like
>this.
With enough bending out, the pins will break off. Be careful.
>What do you mean by correct voltages? It should be max. 5V in that
>whole area of the board. I have no oscilloscope so I can't analyze it
>in detail. I have a standard multimeter that can do resistence,
>voltage, capacity, amps, transistors, tubes and some other stuff. Would
>that be enough to check the voltages on the individual pins?
What I mean is to make sure that the voltages on each pin seem right. 5V
and GND are easy. The 7406 is an open collector inverter so it needs the
1k pull-ups for proper operation. If pin 1 (input) is low, pin 2 (output)
will be high and vice-versa and for each inverter set (3 in/4 out, 5 in/6
out, 9 in/8 out, 11 in/10 out, 13 in/12 out).
>I thought,
>since signals change so fast there is no way to measure the voltages
>other than Vcc and GND with a standard multimeter... hey, my
>electronics knowledge is still *BASIC* but it's growing slowly. :-)
If you're not using the port, the voltages on the pins will not be
fluctuating.
>> TTL chips (74xx series) are very hardy. Their pins can take shorts to both
>> GND and Vcc. It's only Vcc over-voltages that can hurt, but that would be
>> affecting most of the chips in the machine.
>
>... that's good news. So maybe the chips are not fried after all. They
>definitely shouldn't have to stand over-voltages because where in the
>whole system should be anywhere over the max. 12V (a little more to be
>precise) that comes from the 12V DC input power supply...?
There's no 12v here. The diodes are in this circuit to prevent voltage
spikes (+ or -) to be absorbed.
>Yesterday, I also had the strange effect again that taking out the 7406
>for checking purposes would not give me a picture *once* when powering
>on again. So I suspect a slack joint at the 4066 (U21) because they are
>next to each other and I touched it when removing the 7406. Strange
>enough, the picture immediately came back when powering it on the next
>time. Maybe U21 has a slack joint (too)? I'll check that... In any
>event, a slack joint on U21 shouldn't affect operation of U22 because
>they have nothing to do with each other according to schematics.
No, the 4066 is used as a switch for the POT lines. No relation.
By slack joint, do you mean a bad solder joint? If you suspect one, you
can simply re-solder the joints.
>Please allow me a dumb question: In the schematics the small boxes
>representing the inverter gates of U22 have a "1" printed inside them.
>What does that mean?
I have no idea. I'm looking at schematic #252312 as it seems to match what
you have, and I see the "1" as well. Doesn't make sense to be. Even the
symbol for the inverter is non-standard.
Regarding your question about RP6 and the resistance difference on pins 4
and 6... they are the only ones that connect back directly to the 6522. I
suspect that the port resistance is in parallel and changing the values.
Also, I assume you are checking things with no drive connected to the
serial port.
PS.
Andreas Beermann
>
> > ... I was just curious and checked RP6, the 1k Ohm SIL resistor array.
>
> ... hmm, it's not RP6. I've exchanged that with a definitely good one
> (tested before soldering in) from another board. It now shows the same
> odd behavior on pins 4 and 6. And the old one which I have soldered out
> shows proper 1k Ohm on *all* pins. It's interesting that a resistor
> changes its value when soldered in. Or that'd mean there is some
> parallel resistance which is lower (~670 Ohm)...
> --
> cul8er
>
> Paul
Hallo Paul,
to make the search more systematic please try to do the following:
1. check if you've connected something to the user port that's
fiddling arround with pin 9 which is shared with the ATN pin!
if no:
2. please check if it's OK after removing CR9,CR11-17. If yes, re-
insert one diode after the other (polarity must be correct!) or Simply
replace all with new diodes (could also be a 1N4148)
if no (do NOT re-mount the diodes so far!):
3. remove capacitors C88 and C94 and check if it's OK thereafter. If
yes, replace with fresh ones
if no (do NOT re-mount the capacitors so far!):
4. remove the CIA, U22 and RP6. Now all signals of the serial port
(except RESET) should not have contact to *anything* (with the diodes
and capacitors removed as well!)
In case you measure any Ohm-value < 100kOhms from any of the serial
signals to ground you have detected a shortage on the board.
see if that leads you any further...
Andreas
John Guillory
=> ... I have a strange problem I never encountered before. With my
=> C64C,
=> I do LOAD"$",8 and it says SEARCHING FOR $, though no drive is
=> connected. It sees a phantom drive though the DEVICE NOT PRESENT
=> error
=> should occur -- and does with other C64s.
=> I already checked CIA2, U21, U22 and U23 and replaced them with
=> known
=> good parts. The symptom remains.
That sounds like the changeline on PC's... It's a pain in the
ass....
The drive never notices that the drive changes the disk....
Paul Förster
On 2009-11-09 09:26:25 +0100, Andreas Beermann <andreas...@lycos.de> said:
> Hallo Paul,
> to make the search more systematic please try to do the following:
> 1. check if you've connected something to the user port that's
> fiddling arround with pin 9 which is shared with the ATN pin!
... there's nothing there. In fact, the user port pins have been cut
off the edge of the board.
> if no:
> 2. please check if it's OK after removing CR9,CR11-17. If yes, re-
> insert one diode after the other (polarity must be correct!) or Simply
> replace all with new diodes (could also be a 1N4148)
... "unfortunately", the diodes are good. I took them out as you said
and checked them. They block in one direction and show a drop voltage
of 0.53V on the other direction -- all eight of them.
> if no (do NOT re-mount the diodes so far!):
> 3. remove capacitors C88 and C94 and check if it's OK thereafter. If
> yes, replace with fresh ones
... also, no effect. :-(
> if no (do NOT re-mount the capacitors so far!):
> 4. remove the CIA, U22 and RP6. Now all signals of the serial port
> (except RESET) should not have contact to *anything* (with the diodes
> and capacitors removed as well!)
... I did, as you requested. No effect other than that the C64 won't
power up without RP6. Why is that? Is that because pin 3 of RP6
connects to /RES (pin 34) of the CIAs? Putting it back in (temporarily)
made the C64 power up again.
Caps and diodes are still removed. No change. As I mentioned above I
needed to put in RP6 to power it up and check with the LOAD command.
> In case you measure any Ohm-value < 100kOhms from any of the serial
> signals to ground you have detected a shortage on the board.
... no, everything seems fine, except something I don't understand: CR9
and CR14 have a measurable resistance between anode and cathode, *with
the diodes removed!*. The resistence between both pins of CR9 is ~3.3k
Ohm and the resistence of CR14 is ~3.6k Ohm. Does that effect maybe
come from C4, RP3 and the connection to pin 24 of CIA1?
> see if that leads you any further...
... up to now, unfortunately not. The only knowledge I can reliably
draw from this is that the C64 won't power up without RP6 in place.
I run out of ideas. :-(
--
cul8er
Paul Förster
On 2009-11-09 03:54:40 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
> It's a bit of work what you're proposing. You will need to wire the
> outputs from the 7406 to a serial port as well. You can eliminate the
> diodes from your test, though.
... yes, I know about the lines. In fact, it should only be 5 lines to
the CIA, VCC and GND, also three 1k resistors and the C94 replacement.
> Thinking about the diodes... have you checked all of them? They are there
> for over/undervoltage spikes. It's easy to verify they are OK with the
> diode checker on your multimeter.
... I did. All of them block in one direction and show a drop voltage
of 0.53V in the other direction -- see my answer to Andreas' post.
> With enough bending out, the pins will break off. Be careful.
... yes, I know. That's why I plan to use a socket for the experiment.
Sockets are dirt cheap and I have plenty of them.
> What I mean is to make sure that the voltages on each pin seem right. 5V
> and GND are easy. The 7406 is an open collector inverter so it needs the
> 1k pull-ups for proper operation. If pin 1 (input) is low, pin 2 (output)
> will be high and vice-versa and for each inverter set (3 in/4 out, 5 in/6
> out, 9 in/8 out, 11 in/10 out, 13 in/12 out).
... ok, I did check this. All pin pairs 1/2, 3/4, 5/6, 8/9, 10/11,
12/13 are always the complement of each other, pins 7 and 14 being VCC
and GND. 1 is 4.98V, 2 is 0.xx mV, and so on with each pair.
> If you're not using the port, the voltages on the pins will not be
> fluctuating.
... yes, I saw that. Thanks.
> There's no 12v here. The diodes are in this circuit to prevent voltage
> spikes (+ or -) to be absorbed.
... yes, I know. I was referring to over-voltage that could possibly
fry a 74xx chip. But there's nowhere beyond 12V on the whole board, so
even if there was a short, then it wouldn't be enough to fry a 74xx
chip, right?
> No, the 4066 is used as a switch for the POT lines. No relation.
... no, wait. There are two 4066! One is in U21, which I am referring
to and the other is in U18 next to CIA1. The latter is for POTXY. The
former has direct connections to U7, U8, U6 and to U19. If U21 is
empty, you don't see a picture!
> By slack joint, do you mean a bad solder joint? If you suspect one, you
> can simply re-solder the joints.
... tried that but they measure ok.
> I have no idea. I'm looking at schematic #252312 as it seems to match what
> you have, and I see the "1" as well. Doesn't make sense to be. Even the
> symbol for the inverter is non-standard.
... I took the ones from zimmers.net, put them together and printed
them out on A3. Nicely and clearly readable. :-) But yes, I would have
expected a triangle or that half round thing for gate symbols but they
use rectangles there. That doesn't confuse me much. What confuses me is
the "1" printed inside the rectangle.
> Regarding your question about RP6 and the resistance difference on pins 4
> and 6... they are the only ones that connect back directly to the 6522. I
> suspect that the port resistance is in parallel and changing the values.
> Also, I assume you are checking things with no drive connected to the
> serial port.
... there is no 6522 in a C64. ;-) Yes, I have no drive connected. But
since I had to take RP6 out anyway, as suggested by Andreas, I checked
it off board. And it's proper 1k Ohm on all pins. From my measuring
experience today I take it that the presence of chips in the sockets
can *drastically* influence values. So I can understand Andreas' desire
to take off components to get proper results since today.
--
cul8er
Andreas Beermann
> > if no (do NOT re-mount the capacitors so far!):
> > 4. remove the CIA, U22 and RP6. Now all signals of the serial port
> > (except RESET) should not have contact to *anything* (with the diodes
> > and capacitors removed as well!)
>
> ... I did, as you requested. No effect other than that the C64 won't
> power up without RP6. Why is that? Is that because pin 3 of RP6
> connects to /RES (pin 34) of the CIAs? Putting it back in (temporarily)
> made the C64 power up again.
The 64 was not meant to boot up with the CIA and other parts removed.
I just wanted you to MEASURE the signal lines with an Ohm-Meter - they
should have high impedance against everything. So just measure the
resistance against ground. In case your Ohm-meter displays anything
other than an open connection try to trace the line you have measured
and check if there is anything else in that line. This is to check if
the board/wiring/soldering is OK.
>
> ... no, everything seems fine, except something I don't understand: CR9
> and CR14 have a measurable resistance between anode and cathode, *with
> the diodes removed!*. The resistence between both pins of CR9 is ~3.3k
> Ohm and the resistence of CR14 is ~3.6k Ohm. Does that effect maybe
> come from C4, RP3 and the connection to pin 24 of CIA1?
for CR9 this is OK - you'd have to remove RP3 and CIA1 as well -
otherwise you measure ~3.3k (which you actually do) - so this should
be fine (you can x-check by removing CIA1+RP3 as well).
For CR14 you should have high impedance with CR14+U22+RP6+CIA2
removed. In case not you might have narrowed the problem down to that
line. Did you measure with these parts removed?
Andreas
Paul Förster
On 2009-11-10 09:00:42 +0100, Andreas Beermann <andreas...@lycos.de> said:
> for CR9 this is OK - you'd have to remove RP3 and CIA1 as well -
> otherwise you measure ~3.3k (which you actually do) - so this should
> be fine (you can x-check by removing CIA1+RP3 as well).
> For CR14 you should have high impedance with CR14+U22+RP6+CIA2
> removed. In case not you might have narrowed the problem down to that
> line. Did you measure with these parts removed?
... yes, my measurements were with parts removed. The total of parts
removed now is the following: CIA1, CIA2, RP3, RP6, U22, RP9, RP11-17,
C88, C94
Readings are:
Between anode and cathode of RP9: still 3.3k Ohm
Between anode and cathode of RP14: still 3.6k Ohm
What strikes me as odd is these two readings. The connections between
anodes and cathodes of the diodes should be completely open now with
parts removed, right?
What strikes me as even more odd is, that Ruud's dead board, having
done the same to it for testing and comparison except removing CIA1,
also shows 3.3k between anode and cathode of *both* RP9 and RP14, and
not just for CR9, which I would have expected from your above
statement. Maybe my above readings are NO anomalies?
--
cul8er
Paul Förster
On 2009-11-10 11:16:06 +0100, Paul F�rster <paul.f...@gmx.net> said:
> CIA1, CIA2, RP3, RP6, U22, RP9, RP11-17, C88, C94
... ouch! I meant of course CR9, CR11-17. Dito for the rest of my
previous post as I was referring to the diodes of course. Sorry.
--
cul8er
Andreas Beermann
Hi Paul,
I just looked into various schematics from different hardware
revisions... seems details such as pullup resistors or capacitors vary
a lot over the different versions. Maybe you could first try to find
out which schematic fits to your hardware revision...
I was always looking into this one here:
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.A-left.gif
but maybe you have anoter revision? In case yes, it would also be
worth to look at R28/29/30 maybe?
Would you be able to take some (good!) pictures of your board showing
both sides - esp. around the serial interface? Maybe we can spot the
problem on hte picture! I often do it this way when since I do not
have a microscope or magglass...
Andreas
Paul Förster
On 2009-11-10 13:25:46 +0100, Andreas Beermann <andreas...@lycos.de> said:
> I just looked into various schematics from different hardware
> revisions... seems details such as pullup resistors or capacitors vary
> a lot over the different versions. Maybe you could first try to find
> out which schematic fits to your hardware revision...
> I was always looking into this one here:
> http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.A-left.gif
but
>
> maybe you have anoter revision? In case yes, it would also be
> worth to look at R28/29/30 maybe?
... here's the board's label:
PCB ASSY NO. 250469
PCB NO. 252311 REV.3
I took the same images (left and right), put them together in one image
and printed it in A3. So we both have the same schematics, I guess.
Where are you taking me with R28/29/30? I can't find them neither in
the schematics *nor* on the board. The highest resistor number I can
find on my test board is R19 next to the power switch. And on the board
in question it probably was the same. My test board shows line two from
the above as PCB NO. 252311 REV.4. But beside that, it looks exactly
the same.
> Would you be able to take some (good!) pictures of your board showing
> both sides - esp. around the serial interface? Maybe we can spot the
> problem on hte picture! I often do it this way when since I do not
> have a microscope or magglass...
... I have a normal magnifying glass, magnifying factor 2 times. But
what I do not have is a macro optics for my camera and good lighting.
So you wouldn't probably see much on pictures. I can try if you want
but where can I send them? I don't have a place where I can upload them.
--
cul8er
Paul Förster
On 2009-11-10 13:25:46 +0100, Andreas Beermann <andreas...@lycos.de> said:
> but maybe you have anoter revision? In case yes, it would also be
> worth to look at R28/29/30 maybe?
... ah, I see what you're getting at. There are no resistors R28, R29
and R30. There's only RP6 with 1k Ohm and RP3 with 3.3k Ohm. Also, my
boards do not have the U20 (556) chip. So the other schematics can be
ruled out by both the board/revision number as well as the parts shown
in the schematics.
--
cul8er
Peter Schepers
Paul F�rster <paul.f...@gmx.net> wrote:
So Paul, any updates to your findings?
I'm looking over the schematics again, wondering what else to look for.
Everything is going through U2 for the User port and serial port. Try
measuring the output at the serial port when attempting to load something,
just to see what shifts logic levels or changes.
Try measuring U2 pins 23, 2, 3 and 22. These seem to be some of the
control logic to enable the CIA, with 23, 2 and 3 being active low. They
should be high until you try to do something with the drive.
Peter S.
Peter Schepers
Forget what I wrote before, don't know what I was thinking.
Try measuring your serial port readings without and with a device
connected as follows:
Pin Upluggd Pluggd/off Pluggd/on
--------- ------- ---------- ---------
1 (SRQIN) High Float High
2 (GND) Low Low Low
3 (ATN) High Float High
4 (CLK) Low Low Low
5 (DATA) High High High
6 (RESET) High Float High
First column is no device plugged in the serial port on the C64. Second
column is drive plugged in, but off. Third is drive plugged in and on.
Note that pin 5 switches between high-low-high when a drive is powered up.
Float means the voltage is between 0 (GND) and 5 (Vcc). My logic probe
shows no reading, neither high nor low.
Now, check the 6526 U2 pins below:
Pin State
5 (ATN) Low
6 (CLK out) High
7 (Data out) Low
8 (Data In) Low
9 (Clk in) High
Once again, pin 9 switches between High-Low-High when a drive is powered
on.
Check pin 23 on U2 when issuing a load command, it should trigger
high/low/high as well.
PS.
Paul Förster
On 2009-11-13 04:09:29 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
> Forget what I wrote before, don't know what I was thinking.
>
> Try measuring your serial port readings without and with a device
> connected as follows:
[...]
... I've spent some time measuring all sorts of connections but no new
findings so far. :-( I will have to solder everything in again to try
out what you proposed. I'll do so tomorrow or Sunday. I'm not even sure
I'm looking for shorts of any kind anymore as *all* I check is the same
on Ruud's dead board, except for the 300 Ohm resistence difference
between anode and cathode of CR14.
Could it possibly be a bad PLA (U8)? If that would be the case, then I
would have a replacement PLA which I desoldered from Ruud's dead board.
I don't know though, if that one is good either. :-/ But today, I
bought those 64 pin sockets. So in case I'd really have to desolder the
PLA, I can put a socket under it and try the other one out as well.
Also, when I finally get the board *fully* working again, including all
ports and stuff, I'll reveal what I was up to, what I modified and why
I modified it -- promised! Then you all will understand why I go to
such great lengths to get this specific board fully working again. :-)
I even bought such an expensive tool as a Weller WDD-161V plus an
oil-free compressor to get things straight. Knowing that and knowing
how much money that took already should show how much I am interested
to get it fully working. And once I reveal what has happened if
everything works out then you definitely *will* call me crazy, no
matter if that is a precondition in this group or not. :-P I already
"hear" people say "oh my god! I would never have done that!"
So far, thanks to all of you who helped me in the past and will do so
in the future to get this working. Your help has already given me a lot
of valuable insights.
--
cul8er
Peter Schepers
>
>On 2009-11-13 04:09:29 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
>> Forget what I wrote before, don't know what I was thinking.
>>
>> Try measuring your serial port readings without and with a device
>> connected as follows:
>[...]
>
>... I've spent some time measuring all sorts of connections but no new
>findings so far. :-( I will have to solder everything in again to try
>out what you proposed. I'll do so tomorrow or Sunday. I'm not even sure
>I'm looking for shorts of any kind anymore as *all* I check is the same
>on Ruud's dead board, except for the 300 Ohm resistence difference
>between anode and cathode of CR14.
I've been wondering if were in the right area. When the C64 goes to load
from a device, first it has to check that the device exists by sending a
command on the bus and waiting for a response. I don't think the signal
level of one serial bus comm line can cause this problem.
>Could it possibly be a bad PLA (U8)? If that would be the case, then I
>would have a replacement PLA which I desoldered from Ruud's dead board.
>I don't know though, if that one is good either. :-/ But today, I
>bought those 64 pin sockets. So in case I'd really have to desolder the
>PLA, I can put a socket under it and try the other one out as well.
I don't know. I thought the PLA basically controlled the memory map of the
computer. Maybe it's not enabling U2 when needed (see pin 23 of U2) so the
kernal can't talk to the CIA and it's waiting for a response. That check
is part of the testing sequence I sent.
PS
Peter Schepers
>
>On 2009-11-13 04:09:29 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
>> Forget what I wrote before, don't know what I was thinking.
>>
>> Try measuring your serial port readings without and with a device
>> connected as follows:
>[...]
>
>would have a replacement PLA which I desoldered from Ruud's dead board.
>I don't know though, if that one is good either. :-/ But today, I
>bought those 64 pin sockets. So in case I'd really have to desolder the
>PLA, I can put a socket under it and try the other one out as well.
I didn't realize you were working with one of the newer boards, with the
large 64-pin decoder chip. I've not seen one of those go bad, but the CIA2
line comes directly from it. It's a bear to desolder because of the fine
pins.
I just tried using the C64 without U2 to see if that would work, but no I
still get the "device not found" error.
PS.
Peter Schepers
>findings so far. :-( I will have to solder everything in again to try
>out what you proposed. I'll do so tomorrow or Sunday. I'm not even sure
>I'm looking for shorts of any kind anymore as *all* I check is the same
>on Ruud's dead board, except for the 300 Ohm resistence difference
>between anode and cathode of CR14.
This is on the SRQIN line which is not used by the serial port. I don't
think this has anything to do with it.
>Could it possibly be a bad PLA (U8)?
I tried simulating a bad PLA with the CIA2 line missing (or not working)
to CIA2 (U2) by bending out pin 23 on U2, but it didn't make the error
either.
However, I found a detailed doc online that explained the IEC protocol
very well. Reading it for a while steered me in my original direction. In
order to get the "Searching for..." error there had to be an IEC protocol
failure. The only way that happens is if one of the incoming communication
lines (CLK or DATA) is already in the wrong state (active low, so not
high). It was a comment from your original post that I re-read last night
that tipped me off:
> ... I was just curious and checked RP6, the 1k Ohm SIL resistor array.
> I found that pins 4 and 6 show a resistive value of about 670 Ohm while
> pins 2, 3 and 5 showed the proper value of 1k Ohm. I compared that to a
> good board where all 5 pins show a value of 1k Ohm.
Those two pull-ups for the DATA and CLK lines should not measure lower
than 1K unless something is paralleling them. I think this is the problem.
So I simulated it last night by shorting pins on the serial port. I
shorted GND (pin 2) and CLK (pin 4), but only got a "Device not found"
error. Then I shorted GND and DATA (pin 5) and now the C64 will hang at
the "Searching for...". Note at this point that I cannot RUN/STOP out of
this, and I also had to run with the standard kernal, not JiffyDOS, or
this simulation didn't work.
As I mentioned previously, I've seen this before. It's been a while since
I've seen a C64C board, but I believe they are more that 2 layer boards,
and the traces for DATA and possibly CLK have become somewhat shorted with
something else like a GND or Vcc plane, and likely just between the 7406
and the port. My simple resolution years ago was to cut the traces for
both lines from the CIA2/7406/RP6 to the serial port and run new jumpers.
Your idea to run lines from bent-out pins from CIA2 to an external board
with a 7406 and pull-ups would likely work fine. Did you do this?
You also mentioned that the edge connector for the user port were cut off.
Note that the ATN line goes there (to pin 9), but CLK and DATA do not. I
hope it didn't get affected (shorted) buy the cutting.
PS.
Paul Förster
On 2009-11-13 04:09:29 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
> Try measuring your serial port readings without and with a device
> connected as follows:
>
> Pin Upluggd Pluggd/off Pluggd/on
> --------- ------- ---------- ---------
> 1 (SRQIN) High Float High
> 2 (GND) Low Low Low
> 3 (ATN) High Float High
> 4 (CLK) Low Low Low
> 5 (DATA) High High High
> 6 (RESET) High Float High
... first of all the good news first: *Success*! Yippie! It's working
again. :-)
What has happened: I printed your three posts and started checking. To
start checking, I had to solder everything in again, as I have
mentioned before. After I did that, I found that I didn't receive any
sensible information at all at the serial port pins. So I decided to
recheck my putting a socket under the chips, starting with CIA2 and
then going forward to U21, U22 and U3.
When I decided to put sockets under all chips (except U18 and U23 for
space reasons), I had to learn. I started with the character ROM (ok,
bad decision...). Remember when I asked about the ideal temp to
desolder chips? There was a background to that question of course...
Anyway, I had difficulties getting Kernel/Basic and the character ROM
out successfully. I accidentally made some pins a little too hot and so
a few traces came out with the chip. :-( I measured everything through
according to schematics and put wires where I accidentally ripped off
the traces. I measured everything through and all was good -- so far...
Since the "power supply" is mounted on the corner where CIA2 is
located, I decided to leave that chip in until I have more experience
getting chips off boards. The reason is that that corner is not easy to
work on because of an ugly cap and a voltage regulator sitting there
halfway mounted on top of CIA2 and the CHAR ROM. Some time later, after
practicing desoldering chips I decided to try to get CIA2 socketed
anyway. The funny thing is, I didn't rip anything off but I seem to
have damaged the connections D4-D7 (CIA2 pins 26-29) somehow. Is that a
multi-layer board and I hit some invisible connections in another
layer? Was multi-layer possible back when Commodore printed these
boards? So I decided to re-check *every* pin of CIA2 and the
neighboring CHAR ROM thoroughly again. As it turned out, D4-D7 of the
CHAR ROM was fine but had no connection to CIA2, which according to
plan, it should. So I put four small wires in and soldered the rest in
again (C88, C94, the diodes, RP3 & 6 and sockets for U21, U22 and U3).
Btw., ceramic caps don't have + or -, only electrolytic capacitors do,
right? Since I didn't know + or - of the ceramic lenses I put them in
with the inscription in the direction as they are on the other board.
I checked everything and tried LOAD without a drive connected. A DEVICE
NOT PRESENT error occured as should have. That made me confident and I
checked the first column of your table with the drive unplugged.
Signals appeared as you listed them in column 1. Ok, not all. Pin 1
showed strange values. But you recall that I mentioned the board has
been cut. The connection between pin 1 and the diode has been cut. So I
verified it with Ruud's board and put a wire there too, just for the
sake of completeness, even though SRQIN (what does SRQ stand for
anyway?) is not used. That gave me a high value on pin 1 too. I
connected a drive. Checked it and everything works fine.
Oh, before I forget, Peter, you mention in one of your other posts that
you couldn't RUN/STOP out of the SEARCHING FOR... message. This was
true here too. I could only RUN/STOP+RESTORE out of that message. I
don't know if that's important but I thought I'd mention it.
That's the story.
Peter, a very big thank-you to you! :-) Your tips led me to the right
place to check. Also special thanks for taking the time and undertaking
the effort to try and simulate what would or could be wrong.
Many thanks to Andreas Beermann too by whose advice and tips I learned
a lot of things.
And last but not least, many thanks to Ruud for providing a dead board
which did supply a few replacement parts and which I could use to
compare with my board. Also thanks very much for the CIA
pin-bending-check tip. :-)
That was a real tough one for an electronics newbie like me. But I've
learned a lot. Thanks again. :-) I hope such a desaster never happens
again because it already costed me 10 days which I would have liked to
use for something more constructive. At least I have a very fine and
big printout of the schematics, a new (de-)soldering station and quite
invaluable knowledge now. :-P
--
cul8er
Andreas Meerbann
> a lot of things.
time... ;-)
In case you've enjoyed your experiences a little you might want to
participate in (de.)sci.electronics as well. Loads of people like
Andreas there!
Andreas
Peter Schepers
>
>... first of all the good news first: *Success*! Yippie! It's working
>again. :-)
Even reading through this whole post, I still don't know what was really
wrong. Do you think the traces for D4-D7 were somehow damaged before
starting to try to fix things?
>I accidentally made some pins a little too hot and so
>a few traces came out with the chip. :-( I measured everything through
>according to schematics and put wires where I accidentally ripped off
>the traces.
I found this issue affects the 64C the worst. I despised working on those
as traces would lift or ;plate-through holes would come out...
>Was multi-layer possible back when Commodore printed these boards?
I wish I had one to check. Yes, it was possible.
>Btw., ceramic caps don't have + or -, only electrolytic capacitors do,
>right? Since I didn't know + or - of the ceramic lenses I put them in
>with the inscription in the direction as they are on the other board.
Normal ceramics usually don't have any orientation. Tantalum do, but they
are visibly different.
>Signals appeared as you listed them in column 1. Ok, not all. Pin 1
>showed strange values. But you recall that I mentioned the board has
>been cut. The connection between pin 1 and the diode has been cut. So I
>verified it with Ruud's board and put a wire there too, just for the
>sake of completeness, even though SRQIN (what does SRQ stand for
>anyway?) is not used. That gave me a high value on pin 1 too. I
>connected a drive. Checked it and everything works fine.
SRQin is Serial Request In, and is supposedly unused except it is also on
the tape port. It isn't used in the C64 for the serial port.
>That was a real tough one for an electronics newbie like me. But I've
>learned a lot. Thanks again. :-) I hope such a desaster never happens
>again because it already costed me 10 days which I would have liked to
>use for something more constructive. At least I have a very fine and
>big printout of the schematics, a new (de-)soldering station and quite
>invaluable knowledge now.
Since you seem to not have found any shorts or opens on the serial out
side of the CIA, have you inspected the D0-D3 traces on the board between
the CHAR ROM and the CIA to see where the fault could be?
PS
Paul Förster
On 2009-11-16 11:34:42 +0100, Andreas Meerbann <andi...@gmx.de> said:
> I'll inform this guy about your thankfullness when I meet him next
> time... ;-)
... yes, and give him a beer on my account. :-P
> In case you've enjoyed your experiences a little you might want to
> participate in (de.)sci.electronics as well. Loads of people like
> Andreas there!
... well, I don't do this for enjoyment but rather to revive old
functionality which had been cut off in the true sense of the word. So
I'm doing this with connectors and put them in the case because a
complete board wouldn't fit. So the connectors were cut off. But thanks
for the hint. Should I encounter more problems then I will definitely
look there. After all, there's still the issue with the 50 Hz TOD clock
generation and possibly creating a 5/12V DC & 9V AC power supply
open... But that one has time.
--
cul8er
Paul Förster
On 2009-11-16 16:19:40 +0100, sche...@ist.uwaterloo.ca (Peter Schepers) said:
> Even reading through this whole post, I still don't know what was really
> wrong. Do you think the traces for D4-D7 were somehow damaged before
> starting to try to fix things?
... yes, possibly. I measured everything many times and all the lines
have always measured ok. Only the last time I checked, there was no
connection on D4-D7 on CIA2. I suspect it was hairline cracks or
something. I really don't know.
> I found this issue affects the 64C the worst. I despised working on those
> as traces would lift or ;plate-through holes would come out...
... I never had problems with bridge openings. There seem to be little
rings inside. I only had problems with traces not holding on to the
board anymore.
> I wish I had one to check. Yes, it was possible.
... well, I can't check. At least I don't know how. But at many points
it's hard to see where traces lead because they seem to stop at some
place and not show up on the other side of the board.
> Normal ceramics usually don't have any orientation. Tantalum do, but they
> are visibly different.
... and marked accordingly I figure...
> SRQin is Serial Request In, and is supposedly unused except it is also on
> the tape port. It isn't used in the C64 for the serial port.
... it is on the tape port. And the tape connector worked fine. At
least until my serial repair action. Video and tape connectors will be
next to refit.
> Since you seem to not have found any shorts or opens on the serial out
> side of the CIA, have you inspected the D0-D3 traces on the board between
> the CHAR ROM and the CIA to see where the fault could be?
... I have checked all 40 CIA2 pins. D0 to D3 measure fine from one CIA
to the other. But yes, I had problems getting CIA2 out properly. Maybe
I damaged something on those four lines. I really don't know. At least
up to now, it's working again. :-)
Btw., the strange resistance on RP6 pins 4 and 6 remain. But hey, it's
working. :-)
--
cul8er