Denial

Hi All

I have been given a Donor board to help with repairing an other Vic-20
BUT This is all I get on the screen (See photo)
I have removed the Kernal Rom and fitted a socket tested it in an other Partial operating Vic-20 and it tests ok
I have been over the Motherboard and am Stumped.
Any help would be Appreciated.

Keep Safe

Ray W

That looks like a faulty BASIC ROM. To test if it is without desoldering, if you have any game cartridges then boot with one inserted, and if the game runs then BASIC is faulty. Note, this only works with a cartridge that boots directly at start-up (ie not a Scott Adams adventure)

doug_in_nc wrote: ↑Sat Jul 08, 2023 2:58 pm That looks like a faulty BASIC ROM. To test if it is without desoldering, if you have any game cartridges then boot with one inserted, and if the game runs then BASIC is faulty. Note, this only works with a cartridge that boots directly at start-up (ie not a Scott Adams adventure)

Hi Doug

I have tried with Radar Ratrace, Draw Poker, Penultimate +, Deadtest Diag all to no change ?

? Is there a simple way of testing to prove the Ram ?
I have replaced UE1 - 4114 Ram
I have been over the Motherboard with a CRO and all seems to be OK ?????

The motherboard is the ? CR ? Later version

Thanks
Keep Safe

Ray

Hi All - Doug

Thanks

It turns out to be the Vic 6561-101.
After desoldering and replacing it with a socket and used my VERY Suspect Vic Chip
It now works as do the other 2 Vic-20s that I have been working on.

A Small request :-
Where can I get 3 Vic 6561-101 chips.
I am in Victoria Australia.

Thanks
Keep Safe

Ray

Here's a source for one, possibly two, in the UK

https://www.mutant-caterpillar.co.uk/sh ... ts_id=3689

Joe

audronic1 wrote: ↑Sat Jul 08, 2023 10:46 pm It turns out to be the Vic 6561-101.
After desoldering and replacing it with a socket and used my VERY Suspect Vic Chip
It now works as do the other 2 Vic-20s that I have been working on.

A Small request :-
Where can I get 3 Vic 6561-101 chips.
I am in Victoria Australia.

If you're prepared for a certain level of risk you can try AliExpress. They're not cheap (about AU$26) but there aren't too many options these days.

There is a seller in the UK that seems to have NOS

https://www.ebay.co.uk/itm/404325713722 ... R_yapeKoYg

I don't know if they will ship to AU.

Simon

Hi Simon

Thanks

I have ordered 1 (Vic-20 Vic Chip) from England (EBay)

Keep Safe

Ray

I'm working on an 6560/6561 FPGA replacement, but progress is a bit slow. There's a Discord server at https://discord.gg/DcjEz5b7u6 and a few YouTube videos about stuff at https://youtube.com/@vicenary

I'm going to post my findings here on the 6 donor boards I got from the 8-bit Guy. These boards he considered "BER" as a quick assessment he said he did drew him to the conclusion that they would have taken quite the amount of time to repair, and given that he had a 100 or so boards, that sure makes sense to me. At this point, my conclusion is he pretty much has nailed it so far.

Board 1: It was tough, mostly in that I didn't have a donor board to test out the major components, so I had to spend a lot of time coming up with other ways to test things. I do have a TL-866, so logic I can test. I modified a couple of programs to test the static RAM, and that worked well. A Nop-test breadboarded out caught one bad CPU out of the three included. After that it was scoping things out, and it ran down to VR/W being intermittent. It would come and go by tapping on the board. I swapped the factory Character ROM socket, no dice. Further tapping led me to reflow R15...which fixed the board. That's a bench-tech's nightmare.

Board 2: Easy in comparison (especially since I now have a known good board)...the Video Data Bus wasn't getting to VIC-1...the signal coming from the 74LS133 was not happening. When I tried to swap the chip out, the package broke at two pins....clearly a chip that was badly injured. The board worked after that.

Board 3: ....Yikes!! Even the 555 Timer was toast! I think the 74LS08 and the 74LS00 were the only chips that didn't have some damage. I suspect this poor board saw voltage exceeding 10V on the power rail at some point.

...on to Board 4.

audronic1 wrote: ↑Tue Jul 11, 2023 5:31 pm Hi Simon
Thanks
I have ordered 1 (Vic-20 Vic Chip) from England (EBay)
Keep Safe
Ray

The Vic-20 Vic Chip arrived from England and I was Pleased That the Donor Board Now WORKS
The Computer Passed all the Dead test Cart Tests
Thanks to all who have offer some repair information
keep Safe
Ray

Great job!