Reviving a Vic-20
Miika Seppänen
it. It's earlier, "two-pin power connector" type. Produces black
screen, with constant/occasional flickering on it. When I began to
experiment what's going on there, I once managed to get a blue screen
(that was when I plugged on a datassette), but so far had no luck to
reproduce that.
Of course at first I tried the normal "pull and push" with the
socketed chips, with no difference. The +5v and 9VAC are present, but
the datassette does not work at all, neither do blind load commands.
I've checked Ray Carlsen's pages and some technical trouble shoot
documents (probably used by service person) I once got with a Sx-64,
but there are lots of failures, which cause the black screen, so I'm
looking for ideas where to begin.
I've another Vic-20 which is dead as well, but most of its chips are
soldered, so it's none too easy to try exchanging the chips.
-Miika
Agemixer
You could first experiment by measuring the chip voltages for 6502 and the
VIC with a voltmeter, it may be the power supply. Your description sounds
like some capacitor has gone.
--
Agemixer/Skalaria - "First run, then load."
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Miika Seppänen
wrote:
>You could first experiment by measuring the chip voltages for 6502 and the
>VIC with a voltmeter, it may be the power supply. Your description sounds
>like some capacitor has gone.
I'm suspecting a capacitor too, but it's not easy find replacements in
this city. I made some experiments with a VC-1541, where all 65xx
chips are socketed. At least the CPU seemed to be dead (the 1541 kept
spinning with the CPU from Vic), but it wasn't the only one, as the
Vic doesn't boot with the CPU from the 1541. Fortunately, it didn't
kill that CPU. Shouldn't the +5V lines in user- and cassette ports be
together with the +5V lines on chips? I'll check the chip voltages
next, and then proceed to check the VIA's with 1541. If they're dead
too, then there must have happened something really horrible in poor
Vic's past...
BTW, how hot the logic chips (74LSxxx) are supposed to get normally?
-Miika
Michael Hunter
> BTW, how hot the logic chips (74LSxxx) are supposed to get normally?
My experience is that the Logic chips should normally be cool to the
touch, possibly as warm as the surrounding air.
If they are getting hot, you might look for shorts and try replacing
them with another chip. Discarded PC controller cards are an
excellent source of logic chips. I keep a crate of ISA, and MCA type
controllers under my work bench for parts. You'll also discover that
in addition to logic & controller chips, these discarded boards are an
excellent source of memory chips. You'd be surprised at the number of
controller cards that have some amount of on-board memory.
Remember, replace any chip you de-solder from the VIC-20 with a
socket. This will make future swaps easier, and minimize damage to
the board.
Michael Hunter
mhu...@videocam.net.au
Miika Seppänen
<mhu...@videocam.net.au> wrote:
>My experience is that the Logic chips should normally be cool to the
>touch, possibly as warm as the surrounding air.
>
>If they are getting hot, you might look for shorts and try replacing
>them with another chip. Discarded PC controller cards are an
Actually I'm going to take the Vic to my school, where are much better
instruments for measurements than my own el cheapo-multimeter. I
suspect, that the power supply is broken, and maybe giving too high
current. So far I've found the CPU and VIA1 dead. :( I hope there
won't be more such damages, but it sure looks bad. Anyway I won't
replace any chips, before I've made sure there's nothing that would
kill them right away.
>in addition to logic & controller chips, these discarded boards are an
>excellent source of memory chips. You'd be surprised at the number of
>controller cards that have some amount of on-board memory.
No, I'm not. That's because I've already gathered some old PC-hardware
to be scrapped for CBM's.:) That includes three memory expansion cards
with tens of 4164-chips.
-Miika
Jaque Moreau
> Hello,
>
>> BTW, how hot the logic chips (74LSxxx) are supposed to get normally?
>
> My experience is that the Logic chips should normally be cool to the
> touch, possibly as warm as the surrounding air.
>
> If they are getting hot, you might look for shorts and try replacing
> them with another chip. Discarded PC controller cards are an
> excellent source of logic chips. I keep a crate of ISA, and MCA type
> controllers under my work bench for parts. You'll also discover that
> in addition to logic & controller chips, these discarded boards are an
> excellent source of memory chips. You'd be surprised at the number of
> controller cards that have some amount of on-board memory.
>
Is this also valid for C64?
Agemixer
On Tue, 1 Apr 2003, Miika Seppänen wrote:
> I'm suspecting a capacitor too, but it's not easy find replacements in
> this city. I made some experiments with a VC-1541, where all 65xx
> chips are socketed. At least the CPU seemed to be dead (the 1541 kept
> spinning with the CPU from Vic), but it wasn't the only one, as the
> Vic doesn't boot with the CPU from the 1541. Fortunately, it didn't
> kill that CPU. Shouldn't the +5V lines in user- and cassette ports be
> together with the +5V lines on chips? I'll check the chip voltages
> next, and then proceed to check the VIA's with 1541. If they're dead
> too, then there must have happened something really horrible in poor
> Vic's past...
The +5V should be mostly the same source.
http://www.funet.fi/pub/cbm/schematics/computers/vic20/index.html
> BTW, how hot the logic chips (74LSxxx) are supposed to get normally?
0-70 °C range
Michael Hunter
> Does this mean, you can replayce cbm-chips with e.g. chips from a
VLB-multi-I/O-card?
>
> Is this also valid for C64?
Yes, provided that they are the same type of chip and provide the same
function.
Michael Hunter
mhu...@videocam.net.au
Miika Seppänen
<miika.seppan...@saunalahti.fi> wrote:
>Actually I'm going to take the Vic to my school, where are much better
>instruments for measurements than my own el cheapo-multimeter. I
OK, Fluke said that the chip voltages (and all +5V lines) have about
+5v (+5.02V, actually.) But, when I measured directly from the power
plug, I got +11.8VAC with no load, and ~+11.5VAC under load. With the
CPU and both VIAs removed power reached the CASS MOTOR-line, being
something like +7V. So the external power supply should be defective?
Anyway, since the +5V is there, it should boot somehow, anyway?
>suspect, that the power supply is broken, and maybe giving too high
>current. So far I've found the CPU and VIA1 dead. :( I hope there
One mistake here. Both VIAs were ok, I just tested it on floppy drive
configured nr.9 (guess what went wrong? ;) The CPU is sure dead, but
still won't boot with working one. BTW, no luck with a cartridge,
either. Maybe I'll try to replace all caps from the internal PS (the
+5V seemed a bit noisy with oscilloscope), and then begin to change
the logic chips. Unless someone has better ideas?
-Miika
Michael Hunter
> On Tue, 01 Apr 2003 19:12:00 GMT, Miika Seppänen
> <miika.seppan...@saunalahti.fi> wrote:
> plug, I got +11.8VAC with no load, and ~+11.5VAC under load. With
the
I just checked my VIC-20's power supply, and it reads 11.3 VAC with no
load. AC readings with a Multi-Tester do not always provide the exact
reading you expect. I have seen 18 VAC transformers that read 30 VAC
with a Multi-Tester, and 9 VAC transformers that read 14 VAC without a
load, and 11 to 12 VAC with a load. The examples I just provided were
on new, and known to be good power transformers. The difference
between my 11.3 VAC and your 11.8 VAC reading could simply be the
difference between power standards. I am operating off of 120 VAC @
60 Hz, while you are probably running on 220 VAC @ 50 Hz.
The VIC-20's power brick is rated up to 9 VAC @ 2 amps; if you could
produce an artificial load that is just under 2 amps, you might get a
more useful reading. Be careful not to over-load the transformer.
> CPU and both VIAs removed power reached the CASS MOTOR-line, being
> something like +7V. So the external power supply should be
defective?
Unlike AC current, DC is usually right on the mark with a
Multi-Tester. I would expect readings on the 5 volt line to range
between 4.9 and 5.2 volts. Any higher than 5.2 volts and you're
likely to have trouble.
> Anyway, since the +5V is there, it should boot somehow, anyway?
If you are getting a reading of 7 volts on the 5 volt lines, I would
not expect the system to start up.
I think based on your observations, the actual power "brick" is most
likely ok. It could still be defective, but I think you are most
likely dealing with a problem inside the computer.
The 9 VAC supplied by your power brick is converted into the necessary
DC current inside the VIC-20. This is where I would be looking. You
have stated that the 5 volt circuit seems kind-of "noisy." I'm
guessing that you a seeing an indication that the power isn't "clean."
Capacitors tend to make a little "whistling" sound when they are being
operated outside of their specifications, do you hear any kind of low
whistling sound from any of the capacitors?
Michael Hunter
mhu...@videocam.net.au
Agemixer
On Wed, 2 Apr 2003, Miika Seppänen wrote:
> OK, Fluke said that the chip voltages (and all +5V lines) have about
> +5v (+5.02V, actually.) But, when I measured directly from the power
> plug, I got +11.8VAC with no load, and ~+11.5VAC under load. With the
> CPU and both VIAs removed power reached the CASS MOTOR-line, being
> something like +7V.
Just checked some VIC schematics. The MOTOR line voltage sounds correct,
there is a 6.8V zener to create the motor voltage.
It looks like the 9VAC is only used for motor and user port.
> So the external power supply should be defective?
> Anyway, since the +5V is there, it should boot somehow, anyway?
Yes, unless the voltage is stable enough.
> One mistake here. Both VIAs were ok, I just tested it on floppy drive
> configured nr.9 (guess what went wrong? ;)
heh
> The CPU is sure dead, but still won't boot with working one. BTW, no
> luck with a cartridge, either. Maybe I'll try to replace all caps
> from the internal PS (the +5V seemed a bit noisy with oscilloscope),
How noisy? A 0.4V ripple in the DC must be the maximum.
Have you tried an another power supply yet?
> and then begin to change the logic chips. Unless someone has better
> ideas?
It is better to pass through some signals with oscilloscope with the
another VIC.
> -Miika
Agemixer
On Wed, 2 Apr 2003, Michael Hunter wrote:
> If you are getting a reading of 7 volts on the 5 volt lines, I would
> not expect the system to start up.
That is ok for CASS motor.
> I think based on your observations, the actual power "brick" is most
> likely ok. It could still be defective, but I think you are most
> likely dealing with a problem inside the computer.
>
> The 9 VAC supplied by your power brick is converted into the necessary
> DC current inside the VIC-20. This is where I would be looking. You
> have stated that the 5 volt circuit seems kind-of "noisy." I'm
> guessing that you a seeing an indication that the power isn't "clean."
> Capacitors tend to make a little "whistling" sound when they are being
> operated outside of their specifications, do you hear any kind of low
> whistling sound from any of the capacitors?
In that case, i would suspect a whistling smell and corrosive liquids
accompanying the noise :)
A late notice.. it could be the rectifier bridge with a shorted diode,
too.
Ray Carlsen
> it. It's earlier, "two-pin power connector" type. Produces black
> screen, with constant/occasional flickering on it. When I began to
> experiment what's going on there, I once managed to get a blue screen
> (that was when I plugged on a datassette), but so far had no luck to
> reproduce that.
Miika,
Two things that should be checked first: make sure the fuse clips
inside the computer are tight. If they don't hold the 3A fuse tight enough,
the fuse and clips will get hot and the output voltage will "glitch". Next,
resolder the four bridge rectifier connections on the PC board. That diode
runs pretty hot and can actually unsolder itself over time. Make sure the
mounting screw is holding it firmly against the heatsink or it will
overheat and fail.
The "power supply" for the two-pin powered VIC20 is just a big
transformer. The AC from that tranny is not especially significant. It
either works or it doesn't. All the conversion to DC, filtering and
regulation is done inside the computer... so it runs hotter than the later
VIC20 version which uses the two-voltage "brick" like the C64. Any
significant ripple on the 5 volt line will cause intermittant operation or
the blank screen symptom. I usually start with the active components when
troubleshooting. Filter capacitor failure is actually quite rare in
Commodore computers. When the power supply +5VDC is stable, time to start
with the chips.
Ray
Axell
Agemixer wrote:
> In that case, i would suspect a whistling smell and corrosive liquids
> accompanying the noise :)
And watch the tin can blow through the case ;)
mykrowyre
The cassette doesnt use 9VAC. The motor pin is just a logic motor on/off
pin. The motor is driven by +5VDC. The user port does use 9VAC though...
probably for modems, etc.
For example I'm running my C64 on +5V and +12V, no 9VAC at all.
-tom
Agemixer
The schematics say the opposite? The other voltages to 5VDC are
generated from 9VAC, so we need it for the motor. Look at this:
http://www.funet.fi/pub/cbm/schematics/computers/vic20/251027r2.gif
http://www.funet.fi/pub/cbm/schematics/datassette/cas-08r.gif
Miika Seppänen
wrote:
>The cassette doesnt use 9VAC.
Actually, it does, in both versions of Vic. You are right to the
halfway anyway, because that line is connected between rectifier
bridge and regulator, so it's not AC, but still +9V.
-Miika
Miika Seppänen
wrote:
>resolder the four bridge rectifier connections on the PC board. That diode
>runs pretty hot and can actually unsolder itself over time. Make sure the
>mounting screw is holding it firmly against the heatsink or it will
>overheat and fail.
This rectifier is one component I'm suspecting, as it could be reason
for the "noisy" 5VDC line. When I opened the Vic first time, the
heatsink was a little bit loose, so the rectifier can be failed.
Anyway, it's a cheap part, and easily replaceable, so I'll start with
it before messing with soldered chips. It'll just take some time
before I can get a replacement, but my time is very scarce right now
anyway.
>troubleshooting. Filter capacitor failure is actually quite rare in
>Commodore computers. When the power supply +5VDC is stable, time to start
>with the chips.
This is what I'm going to do, if changing the rectifier doesn't help.
In the meantime my Vic-20CR will get the attention. For some reason it
doesn't seem to reset: The pin 3 on the timer (U36, LM555) goes up to
+5V after power up, then drops down after few seconds. The reset-line
stays high all time and disk drive doesn't reset either. I've yet to
check the schematics, but I believe the CPU is shorted (VIAs and 7406
(UB4) work perfectly, and I didn't notice other chips connected to
reset line.) Unfortunately, testing means unsoldering the CPU, so with
the iron we go...
-Miika