C128 powersupply from 12V DC

SmallCleverDinosaur · January 14, 2009, 06:28 AM

I've been thinking of constructing a power supply for the C128 that runs on 12V DC, like from a car or a boat battery. Does anyone know if such a device already exists?

The C128 needs +5V DC and 9V AC. +5V DC is no match to get from 12V DC, but 9V AC is a litte trickier.

What does the C128 use the 9V AC for? Is it only to supply the Userport with that voltage or is its frequency used internally to create the clockfrequence for the processor? One might suspect that since the NTSC and PAL version differ slightly in speed which might be directly connected to the fact that the US uses 60Hz and Europe and other parts of the world uses 50Hz.

I want to have a power supply which uses as little effect as possible. So "cheating" by using a commercial device like those that turns the DC into AC and transforms it to 110V or 220V is not an option

To then transform it back to +5V DC and 9V AC uses way to much power.

Thoughts anyone?

RobertB · January 14, 2009, 01:33 PM

Quote from: SmallCleverDinosaur on January 14, 2009, 06:28 AM...or is its frequency used internally to create the clockfrequence for the processor? One might suspect that since the NTSC and PAL version differ slightly in speed which might be directly connected to the fact that the US uses 60Hz and Europe and other parts of the world uses 50Hz.

From what I've read, the 9V AC is used to control the TOD clock.

Truly,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug
Catch the Fatman and Circuit Girl on http://vimeo.com

BigDumbDinosaur · January 15, 2009, 02:57 AM

The 9VAC, as noted, runs the TOD clocks in the two CIA chips. It has to be the correct frequency for the type of video system in the 128, 60 Hz for NTSC or 50 Hz for PAL. The CPU clock frequency is generated by a crystal, not the power line frequency.

6502Dude · January 15, 2009, 05:58 AM

Quote from: SmallCleverDinosaur on January 14, 2009, 06:28 AM
I've been thinking of constructing a power supply for the C128 that runs on 12V DC, like from a car or a boat battery. Does anyone know if such a device already exists?

The C128 needs +5V DC and 9V AC. +5V DC is no match to get from 12V DC, but 9V AC is a litte trickier.
Thoughts anyone?

Why not use a 555 timer, a few resistors, and a couple of transistors to generate 60hz.
I don't think it is critical that 60hz be a sine wave and current requirements are modest (unless using cassette drive).
I think someone has aready done this, but I can not recall where I saw it.

6502Dude · January 15, 2009, 06:26 AM

Quote from: BigDumbDinosaur on January 15, 2009, 02:57 AM
The 9VAC, as noted, runs the TOD clocks in the two CIA chips. It has to be the correct frequency for the type of video system in the 128, 60 Hz for NTSC or 50 Hz for PAL. The CPU clock frequency is generated by a crystal, not the power line frequency.

I thought video chip (CRT controller) clocking was derived off crystal as well.
Registers in values within CRT controller set the division of clock input to establish horizontal sync pluse (postion & width), Vertical Sync pulse interval (50hz/60hz), scan lines per row, etc.

As far as I know, 9VAC 60hz signal is completely independant of (and not relevant to) video system of C128.

SmallCleverDinosaur · January 15, 2009, 07:07 AM

Quote from: 6502Dude on January 15, 2009, 05:58 AM
Why not use a 555 timer, a few resistors, and a couple of transistors to generate 60hz.
I don't think it is critical that 60hz be a sine wave and current requirements are modest (unless using cassette drive).
I think someone has aready done this, but I can not recall where I saw it.

That's an interesting idea

Could you make a rough drawing of that kind of circuit? Just to have something to begin with

I have also been thinking of what type the 60Hz (or 50Hz) has to be, if it has to be sine or if it's enough that it's some sort of square wave. What kind of wave would your circuit create?

Quote from: 6502Dude on January 15, 2009, 06:26 AM
I thought video chip (CRT controller) clocking was derived off crystal as well.
Registers in values within CRT controller set the division of clock input to establish horizontal sync pluse (postion & width), Vertical Sync pulse interval (50hz/60hz), scan lines per row, etc.

As far as I know, 9VAC 60hz signal is completely independant of (and not relevant to) video system of C128.

You mean you don't think the 9V AC is needed at all? That the C128 could be run on only +5V? Without some functions of course. Like the cassette and the 9V in the Userport etc. But that it would actually start on just +5V?

megabit · January 15, 2009, 11:22 AM

Hi all, I went over the schematics for the C128 and found where +12V
is used at U5 SID 6581, also transistor Q2 that supplies the Audio
Output.

It also supplies bias to the base of Q6 which supplies 'ph1 in' to
the Z-80 processor. There is a section in the service manual that
explains the reason for this circuit. Here is a quote from the manual:

"One additional problem that arises in clocking the Z-80 is that while all
of the 8502 levels, and most of the Z-80 levels, are TTL compatible,
the Z-80 clock input expects levels very close to five volts. For that reason,
the output from the VIC chip is processed by a transistor switching circuit
to give a full amplitude clock. This circuit uses the nine volt supply, thus,
the nine volt circuit must be operational for the Z-80 to function."

I can tell you from an experience I had if that circuit is not working when the +5 volts comes up, the computer will not work.

Dan...

megabit · January 15, 2009, 12:44 PM

Also, the 9vac has to be isolated from ground. So if you make a switching circuit, you will have to connect a transformer to the output of the switching circuit and use the secondary of the transformer for 9vac.

Dan...

RobertB · January 15, 2009, 03:37 PM

Quote from: megabit on January 15, 2009, 11:22 AMFor that reason, the output from the VIC chip is processed by a transistor switching circuit to give a full amplitude clock. This circuit uses the nine volt supply, thus, the nine volt circuit must be operational for the Z-80 to function."

I can tell you from an experience I had if that circuit is not working when the +5 volts comes up, the computer will not work.

Very interesting. Thanks for the information.

Truly,
Robert Bernardo
Fresno Commodore User Group
http://videocam.net.au/fcug
Other Group of Amigoids
http://www.calweb.com/~rabel1/
Southern California Commodore/Amiga Network
http://www.sccaners.org/

SmallCleverDinosaur · January 15, 2009, 06:59 PM

Quote from: megabit on January 15, 2009, 11:22 AM

Hi all, I went over the schematics for the C128 and found where +12V
is used at U5 SID 6581, also transistor Q2 that supplies the Audio
Output.

It also supplies bias to the base of Q6 which supplies 'ph1 in' to
the Z-80 processor. There is a section in the service manual that
explains the reason for this circuit. Here is a quote from the manual:

"One additional problem that arises in clocking the Z-80 is that while all
of the 8502 levels, and most of the Z-80 levels, are TTL compatible,
the Z-80 clock input expects levels very close to five volts. For that reason,
the output from the VIC chip is processed by a transistor switching circuit
to give a full amplitude clock. This circuit uses the nine volt supply, thus,
the nine volt circuit must be operational for the Z-80 to function."

I can tell you from an experience I had if that circuit is not working when the +5 volts comes up, the computer will not work.

Dan...

Thank you, that was very good information!

I read here about a guy that has put his C64 in a PC case and used the internal powersupply from the PC to power the C64. But it was foolish of me to beleive that this could work for the C128 since it's so much more sophisticated

As we all know, the C64 doesn't have a Z80 but the C128 can't live without it.

Mathias Roslund · June 05, 2009, 05:21 PM

The IDE64 guy has schematics for a 12V DC to 9V AC converter here. I wonder why nobody with the required tools and knowledge offer something like that for sale. I would buy a bunch for sure, and I can't be the only one who have old PSU's which may fail at any time, killing the C64/C128... I know protovision used to sell modified PC PSU's for use with C64/C128, so they must have been using some kind of converter.

bacon · July 09, 2009, 04:10 PM

Quote from: Mathias Roslund on June 05, 2009, 05:21 PMI know protovision used to sell modified PC PSU's for use with C64/C128, so they must have been using some kind of converter.

I have one of those which I use to power all my Commodores (C64, C128, VIC 20, Plus/4) as well as my 1541-II. The 9VAC comes from a 240VAC to 9VAC transformer that's been added to the PSU. I higly recommend it; it's professionally built and you'll never lose any more sleep worryingg about your old PSUs killing your Commodores.

carlsson · July 09, 2009, 10:38 PM

Quote from: Mathias Roslund on June 05, 2009, 05:21 PMThe IDE64 guy has schematics for a 12V DC to 9V AC converter here

I believe that circuit has been discussed in other forums, and it is thought to be sub-optimal since it outputs a square wave rather than sinusoid. It probably works, just like a 8V or 10V AC power source might also work if you can't get 9V. As Bacon writes, the Protovision Heavy Duty supply uses an external 9VAC transformer. We've had a bit of discussion on making your own power supply at the VIC-20 forum Denial, but the conclusion was it requires a lot++ of experience to safely design one and it is hard to get a perfect design without spending a significant amount of money.