Faulty C128: need help

[Sasha]

(Sorry for my poor English.)

All greetings! Help to resolve, please, a problem with С128. At transition in a graphic mode the information in memory is lost (i.e. I type, for example, GRAPHIC1, it in columns. The mode passes. If press after that any buttons on the screen there is a blinking dust. By pressing dump the dust continues to blink until there will be firm message Cmmodore Basic). Any game does not work. Ð"емы too. At start of the computer the volume of free memory is defined correctly... The Editor спрайÑ,ов does not work (since the count uses. A mode). In what there can be a problem? I have thought that the problem can be in memory regeneration in a graphic mode...

Some screenshots are on http://zx.pk.ru/showthread.php?p=247485#post247485 (Original thread) Help me, please!
Thanks!

[Sasha]

Yesterday I noticed, that screen of my c128 becomes lighter and lighter... I don't know what is it, but I think that it is broken VIC. I haven't got spare parts to test... 

[bacon]

It sounds like it could be the VIC chip, but it could also be the power supply. Do you have another power supply you can try? Also, have you tried C64 mode and C128 mode with the 80-column display?

[Sasha]

I don't have another PSU, but I checked all the voltages. They are good. VDC, SID and CIAs are good. C64 mode works well only in text mode... Games and demos doesn't work, but some intros works well. I also think, that it is broken VIC. Is there some program to test VIC chip? I can't replace VIC, because I haven't got another one. But I have two C64Cs with good ones. But, as I know, I can't replace C64 VIC with C128 VIC...

[Sasha]

Unfortunatelly I couldn't find spare VIC-IIe chip to test my C128. Does anybody know how can I connect VIC-II from my C64? Which extra registers should I add? I'll make it on additional handmade PCB. I wand only to test c128 and make sure, that the VIC chip fails...

[Sasha]

Some ideas. As I understand, the Ф0 signal taken from C64 VIC is the same as 1MHz output taken from C128 VIC. That's OK. I needn't make 2MHz output, because it only clocks SID chip, OK? Well, I only need to generate Z80PHI output. As I inderstood, I shound divide dot clock by 2, AND it with then 1MHz clock and it would be Z80PHI? Is it OK? Need I emulate extra registers for external keyboard support or C128 will start without it?

[Sasha]

External clocking device for Z80PHI is working well. 1MHz signal is given instead of 2MHz. Now I'm working at building the cross-panel for 8565 VIC.

[Sasha]

Yup, IT WORKS!!!    The main problem was generating MUX signal. I passed RAS through two invertors, and it began to work!!!!!!!!! I could watch Edge of Disgrace demo to the end without any troubles! It seems that C64 mode is OK. In C128 additional keys are not working and turbo-mode doesn't work. That's OK!!! Now the main headache is where could I find 8566 VIC to replace broken one?

[Sasha]

Maybe, someone from Europe could sell me one spare 8566 VIC? It is almost impossible to find Commodore parts in my country...

[Hydrophilic]

Sorry I don't have an 8566 to offer you, but I wanted to say that's pretty cool that you replaced VIC-IIe with VIC-II original, with Z80 clock cirucuit of course.

Could you tell us more about the Z80 clock circuit you made?  You said it only works at 1MHz instead of 2MHz, why is that?  Did 2MHz not work, or maybe you were in a hurry and 1MHz was easy and you never tried 2MHz?

The reason I ask, is I still think it should be possible to run Z80 at 4MHz if it uses both phases of PHI0, like the 8502 does when it runs at 2MHz.

Anyway, I'm glad you got it to work.

[Sasha]

I divide DOT CLOCK by 2 using RS-trigger (soviet 1533ТМ2). Then I AND this signal with 1MHz clock. Thus I have inverted clock for Z80. The I pass this signal through invertor. Now it is normal Z80 PHI clock. It was made accordingly to diagrams from "C128 Service Manual".


The another problem was with MUX signal. There were no diagrams of shis signal, and I began to experiment with it. I connected this pin directly to RAS, but C128 won't start... Then I passed this signal through two invertors as a buffer. And IT BEGAN TO WORK!!!

I haven't done 2MHz mode because it requires emulation of additional register. It wasn't necessary for me to make full compatible part because I only wanted to test if VIC chip was broken.

[Hydrophilic]

Thanks for the description.  I guess I need to look at the service manual for some ideas.  I hope you find an 8566!

[Sasha]

Thank you, I think so.

[Sasha]

Here are some photos of my C128.
http://sash-a.nm.ru/photos/SDC13043.JPG
http://sash-a.nm.ru/photos/SDC13044.JPG
http://sash-a.nm.ru/photos/SDC13048.JPG
http://sash-a.nm.ru/photos/SDC13050.JPG
http://sash-a.nm.ru/photos/SDC13051.JPG
http://sash-a.nm.ru/photos/SDC13052.JPG

[Hydrophilic]

Thanks for the photos.  That is really an impressive (if messy) engineering feat!  Anyone who would go through all that trouble is a true Commodore fan.  I'm glad you got the old VIC2 to work, but now I can see why you need a real 8566.

[Sasha]

If you're interested, here are some photos of my Amiga Kickflash project (modified DC-KF500.lha) http://zx.pk.ru/showpost.php?p=172022&postcount=45
And it isn't the most difficult project I've made