Why doas the C64 mainboard need 9V AC ?
Alexander Krauss
Hello,
First a little preface: I built a C64 with a 1541, a 1581, a modem and
powersupply (from a PC) in a PC chassis. I turned on all, and after some
while everything worked just fine.
BUT ONE THING I CAN'T UNDERSTAND IS: I turned on the C64 (removed the 7812
and 7805 regulators (5V and 12V supply) and directly connected the PC
suuply to it. fine. BUT the C64 still seems to need the 9V from the C64
powersupply somehow, because without switching the C64 9V AC (!!) on
at the same time I switch the DC voltages on, the C64 won't come up.
)
Any idea why the C64 need the 9V AC on his mainboard ?
I personally have no idea.
Alex.
.
Kevin Horton
-> BUT ONE THING I CAN'T UNDERSTAND IS: I turned on the C64 (removed the 7812
-> and 7805 regulators (5V and 12V supply) and directly connected the PC
-> suuply to it. fine. BUT the C64 still seems to need the 9V from the C64
Did you remember *both* 5 volts; i.e. there's a seperate 5V reg in the
power supply cube, and a 7805 reg on the board
-> powersupply somehow, because without switching the C64 9V AC (!!) on
-> at the same time I switch the DC voltages on, the C64 won't come up.
-> Any idea why the C64 need the 9V AC on his mainboard ?
The 60 (or 50)Hz interrupt signal from the AC is used to run the computer.
If you inject a 60Hz signal into the appropriate place, it'll work just
fine. I can't remember the location exactly. (/IRQ on the uP?)
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Mike Paull
Alexander Krauss (sz0...@cd4680fs.rrze.uni-erlangen.de) wrote:
: Hello,
: First a little preface: I built a C64 with a 1541, a 1581, a modem and
: powersupply (from a PC) in a PC chassis. I turned on all, and after some
: while everything worked just fine.
: BUT ONE THING I CAN'T UNDERSTAND IS: I turned on the C64 (removed the 7812
: and 7805 regulators (5V and 12V supply) and directly connected the PC
: suuply to it. fine. BUT the C64 still seems to need the 9V from the C64
: powersupply somehow, because without switching the C64 9V AC (!!) on
: at the same time I switch the DC voltages on, the C64 won't come up.
: )
: Any idea why the C64 need the 9V AC on his mainboard ?
I believe that the timing is derived from the AC.
Mike
psapp
RS-232 work (9V AC is rectified and filtered to make +12vdc & -12vdc by
using a floating ground bridge rectifier. An IBM PC power supply can be
used if the +12vdc & -12vdc supply leads are run into the 9v AC in on the
C=64.
Jeff Hunsinger
signal. You need to recreate it using an oscillator circuit of some sort.
Jeff
Jani 'Holle' Holopainen
I have a vic-20 and its kinda same thing as c64. I have also wondered
this 9v AC mystery. In my vic AC goes directly to two pins in user port.
It isn't connected to anything at mainboard!
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80160 JOENSUU | Email: jhol...@cs.joensuu.fi
Alexander Krauss
: : Any idea why the C64 need the 9V AC on his mainboard ?
: I believe that the timing is derived from the AC.
What timing ? What can someone do with the powerline frequency of 50 (PAL)
or 60Hz (NTSC) BTW.: It can't be for distinguishing PAL/NTSC because
there's already a jumper near the VIC.
: Mike
Philip Arny
how do you wire that? +12v into the AC9volt pin, other AC9volt pin to ground,
or do you have to run those volts into the case?
Philip
Mike Neus
Mike Neus
EricL5041
As I stated in another reply. The 9vac is only used to create a
second 5vdc and the 12vdc. The ac is sent to the user port and then to a
gate where it is converted to a square wave and sent on to the two CIA
chips. These are the only places I see the 9vac used.
According to my schematics the video oscillator is derived from a
crystal. Also another message on my post clarified the dual 5v supplies
as one for logic and one for video.
Jim Brain
> The 9V AC is delivered to the User Port for the MC1488 line drivers for
> RS-232 work (9V AC is rectified and filtered to make +12vdc & -12vdc by
> using a floating ground bridge rectifier. An IBM PC power supply can be
> used if the +12vdc & -12vdc supply leads are run into the 9v AC in on the
> C=64.
>
Sorry to disappoint, but this is not correct. I wish it were, but it isn't.
The 9volt is present to get the 60Hz cycle for the 6526 TOD clocks I
believe, and for sure I know it is rectified on the board to 9v DC or
12 v DC for the SID chip.
I seem to recall the cassete unit on the 64 and VIC need AC for some
reason, but don't quote me on that one.
9 VAC is placed on the user port, and I think even the exp port, but
just for people to use, not with anything coded into it.
jim
--
Jim Brain, Embedded Systems Designer, Brain Innovations.
br...@msen.com
Dabbling in VR, Old Commodore Computers, and Good Times!
"The above views DO reflect my employer, since I am my employer" - Jim Brain
Harlekin/FairLight
>
> The 9V AC is delivered to the User Port for the MC1488 line drivers for
> RS-232 work (9V AC is rectified and filtered to make +12vdc & -12vdc by
> using a floating ground bridge rectifier. An IBM PC power supply can be
> used if the +12vdc & -12vdc supply leads are run into the 9v AC in on the
> C=64.
>
I think Commodore removed the 9V AC output in one version of the C64.
Of course the result was some RS232 interfaces did not work!
Newer Interfaces using MAX232 drivers (5V DC) should work correctly.
/Magnus
Wes Shull
(Jani 'Holle' Holopainen) wrote:
Alexander Krauss (sz0...@cd4680fs.rrze.uni-erlangen.de) wrote:
` Any idea why the C64 need the 9V AC on his mainboard ?
Ok, to end this once and for all, from the schematic:
9VAC comes in across pins 6 and 7 of CN7, the power connector
All these things are done with it:
1) it is regulated down to produce the +12v supply (9VAC RMS >12VDC
2) it is regulated down to produce a second, low current +5v supply
3) it is noise-filtered and passed to CN2 (the user port)
4) it is very sloppily rectified and used to power the cassette motor
5) it is used to derive the 60 Hz TOD clock for the 6526 CIA chips
As a bit of trivia, in the SX-64 (anyone want to buy one? not perfect
condition, but works fine) the only use the 9VAC signal has is to go to
the user port; the +5VDC and +12VDC signals are derived separately, I
don't think it has a cassette port, and the TOD is generated with a can
oscillator. This came out useful for me, as the primary transformer of my
SX-64's power supply died and I couldn't find the proper dual-secondary
type to replace it. Instead, I replaced it with a normal 1A 12.6V
transformer and skipped the 9V section altogether, and it works fine. Of
course, I can't use my 1660 on the user port now, but the excessive 9VAC
current draw is probably what killed the transformer in the first place
(and is probably why you can't plug one in without applying a hacksaw to
the 1660 case first). This is also useful in that you could build an
internal battery pack for the SX-64 without having to synthesize 9VAC...
--
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Bruce James Robert Linley
>In article <1995Mar31.0...@cs.joensuu.fi>, jhol...@cs.joensuu.fi
>(Jani 'Holle' Holopainen) wrote:
>
>Alexander Krauss (sz0...@cd4680fs.rrze.uni-erlangen.de) wrote:
>
>` Any idea why the C64 need the 9V AC on his mainboard ?
>
>Ok, to end this once and for all, from the schematic:
>
>9VAC comes in across pins 6 and 7 of CN7, the power connector
>All these things are done with it:
> 1) it is regulated down to produce the +12v supply (9VAC RMS >12VDC
> 2) it is regulated down to produce a second, low current +5v supply
I noticed this too on the schematic and was wondering, why a larger
regulator, like an LM323 (5V3A) wasn't used instead (and then used
to power the whole motherboard). The added cost of the regulator
would be more than recovered by the simplification of the external
power supply, which could now supply 9VAC exclusively.
I think the early VIC-20s (with the 2 prong power plug) had an AC only
supply, until they changed the design to use the same power supply as
the C64 (7-pin din plug). I may be wrong. Haven't seen a VIC-20 for
some time now.
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Marko Mäkelä
EricL5041> As I stated in another reply. The 9vac is only used
EricL5041> to create a second 5vdc and the 12vdc. The ac is sent to
EricL5041> the user port and then to a gate where it is converted to a
EricL5041> square wave and sent on to the two CIA chips. These are
EricL5041> the only places I see the 9vac used.
You forgot one thing: the unregulated +9V signal for the transistors
that drive the cassette motor. Maybe the absence of this signal puts
the two transistors (or actually one of them is a darlington pair) in
the wrong operation mode.
EricL5041> According to my schematics the video oscillator is
EricL5041> derived from a crystal. Also another message on my post
EricL5041> clarified the dual 5v supplies as one for logic and one for
EricL5041> video.
True.
Marko
Jim Brain
lin...@netcom.com (Bruce James Robert Linley) wrote:
> In ye olden post shul...@uidaho.edu (Wes Shull) spake...
> >In article <1995Mar31.0...@cs.joensuu.fi>, jhol...@cs.joensuu.fi
> >(Jani 'Holle' Holopainen) wrote:
> >
> >Alexander Krauss (sz0...@cd4680fs.rrze.uni-erlangen.de) wrote:
> >
> >` Any idea why the C64 need the 9V AC on his mainboard ?
> >
> >Ok, to end this once and for all, from the schematic:
> >
> >9VAC comes in across pins 6 and 7 of CN7, the power connector
> >All these things are done with it:
> > 1) it is regulated down to produce the +12v supply (9VAC RMS >12VDC
> > 2) it is regulated down to produce a second, low current +5v supply
> >[snip]
>
> I noticed this too on the schematic and was wondering, why a larger
> regulator, like an LM323 (5V3A) wasn't used instead (and then used
> to power the whole motherboard). The added cost of the regulator
> would be more than recovered by the simplification of the external
> power supply, which could now supply 9VAC exclusively.
>
> I think the early VIC-20s (with the 2 prong power plug) had an AC only
> supply, until they changed the design to use the same power supply as
> the C64 (7-pin din plug). I may be wrong. Haven't seen a VIC-20 for
> some time now.
You are right about the VIC. Why was it done this way?
Why did the VIC have so many 1K*8 RAM chips when 4K ones were just as cheap?
CBM was overstocked on 1K RAM. True story....
Jim
Wes Shull
` In ye olden post shul...@uidaho.edu (Wes Shull) spake...
` > 2) it is regulated down to produce a second, low current +5v supply
`
` I noticed this too on the schematic and was wondering, why a larger
` regulator, like an LM323 (5V3A) wasn't used instead (and then used
` to power the whole motherboard). The added cost of the regulator
` would be more than recovered by the simplification of the external
` power supply, which could now supply 9VAC exclusively.
Heat dissapation. You don't want all that heat building up in your poor
'lil 64 (ever notice how warm it gets on the bottom as it is?) The reason
for not putting the whole 5V section in the brick is, like someone else
said, so you can derive a separate, lower-noise, better-regulated version
for the chips that need it, and the less distance between where it is
regulated and where it used the cleaner it is.
Mike Neus
Jeffery C McLean
: In article <linleyD6...@netcom.com>, lin...@netcom.com (Bruce James Robert Linley) says:
: >
: >In ye olden post shul...@uidaho.edu (Wes Shull) spake...
: >I noticed this too on the schematic and was wondering, why a larger
: >regulator, like an LM323 (5V3A) wasn't used instead (and then used
: >to power the whole motherboard). The added cost of the regulator
: >would be more than recovered by the simplification of the external
: >power supply, which could now supply 9VAC exclusively.
: If you look at the same schematic, you'll also notice that the second five
: volt supply is used only by the VIC chip. My guess is they were trying to
: eliminate/reduce noise to the VIC, hence the video display.
: As far as the VIC 20 supply goes, I did not realize there were two supplies.
: That is kinda strange, but, prehaps since the 64 needed a new supply, C= saw
: fit to retro-fit the Vic-20 to use it, thus they only needed to make one
: power supply for two computers. Just a passing thought, mind you.
Sence the Vic20 origanly had a curcit in it to convert 9v ac to 5v dc
(or similer) It only needed the origanl 9v...
The C64 from what I have seen needs more amps than the Vic and converting
a 9v to 5v would result in a less that satifactury sorce of power...
So the powersuply was designed to suply the corect voltages from the start
this is also a cheaper power suply than having a 9v and then paying for
the conversion curcut. So by refitting the Vic20 to the same the cost
of preduction is droped... I noticed however that the 64 prototypes
(I saw one) used the old Vic20 9v line... It may have also just been
a mas production thing.. Commodore finding it's cheaper to make it
with the transformer giving 9 and 5 volt lines and convert the 5v ac to
5v dc rather than having to work with it once it's in the computer...
But over all I belave commodore did it to drop costs...
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http://www.ccnet.com/~felinoid/
Andreas Boose
> If you look at the same schematic, you'll also notice that the second five
> volt supply is used only by the VIC chip.
Not only the VIC chip. The whole clock generation (74LS629, 74LS74,
74LS193, MC4044) and the 3 transistors between the VIC chroma/luma output
and the modulator are fed with "CAN +5V" (the second 5V supply).
> My guess is they were trying to
> eliminate/reduce noise to the VIC, hence the video display.
Yes, but on screen there are still these ugly vertical shadow-strips every
8 dot-clocks. I've never seen any C64 without this 'noise' problem. :-/
MfG Andreas