exxos's Atari, Amiga & retro forum

Well I my friend of some 50 years gave me a bag with a atari 2600 disassemble in it. The capacitors were cut out the voltage regulator had a corner blow out of it. So I started the wall adapter was dead as a door nail. Have one of those on order. On to the regulator removed the 7805 put a new one in. Found my cap supply replace the large arial with a audio grade. Then on the 4.7 uf cap hmm only had tantalum axial 4.7 35v on I go. Now I put the machine on a bench psu put 9vdc in and a perfect 5.01 comes out. For about 10 seconds frogger kind of came up on the screen with lots of missing blocks and horrible sound then the black screen with a ntsc label and that was it. Were to goto next after a chip reseat any ideas?

Tom

Well there aren't many options inside a 2600!!

The RAM, all 128 bytes of it, is located in the 6532 RIOT, and then there is 4KB ROM and some carts may have extra RAM too.

If Frogger appeared briefly, I'd suggest that the first thing would be a good clean of the cart slot contacts and the cart edge connector with IPA, then a spot of DeOxit or similar.

Then perhaps check continuity on all the address/data bus lines.

My spare 1050 is basically half a 2600, as it has a 6507 and 6532 RIOT too, though it does also have a dedicated extra 128 bytes RAM on board

@rubber_jonnie

I am going to put the scope on the clock and data lines will look at the address bus to the cpu has 12 address lines and 8 data should go quick will post more later with pictures also i will get to cleaning it there may have been pop spilled on it before it was taken apart.

Tom

Tomswork wrote: ↑Thu Nov 25, 2021 3:07 pm @rubber_jonnie

I am going to put the scope on the clock and data lines will look at the address bus to the cpu has 12 address lines and 8 data should go quick will post more later with pictures also i will get to cleaning it there may have been pop spilled on it before it was taken apart.

Tom

Cool, sounds good

@rubber_jonnie


Well I have this now after recap and 4050 replacement and chips cleaning and reset there is a lot of missing screen information and no sound any ideas for the next step

Tom

@Tomswork Having looked again, I'm going to change my earlier statement that carts sometimes had 4KB RAM to carts had up to 4KB RAM and special carts had up to 64KB RAM using bank switching.

All 2600s had 128B 'scratch RAM' as this was contained in the 6532 RIOT chip.

It looks like there are bits missing in the display RAM, so if it's doing it on all cartridges, I'd have to suspect the edge connector as that is the primary connection from the 2600 to the onboard cartridge RAM.

Do other carts work or exhibit the same problem?

Are the games actually working, as in you can play them?

@rubber_jonnie

all the cartridges have problems with the video even the simple 2k and 4 k ones the sockets in the pcb are single sided pin contacts i will ring them out see what there up to i ordered another 6532 they are cheap I have to fix the joysticks before I can move on to a game test

Tom

Tomswork wrote: ↑Mon Dec 06, 2021 3:15 pm @rubber_jonnie

all the cartridges have problems with the video even the simple 2k and 4 k ones the sockets in the pcb are single sided pin contacts i will ring them out see what there up to i ordered another 6532 they are cheap I have to fix the joysticks before I can move on to a game test

Tom

I can't imagine all the carts are bad, but the 6532 RIOT is definitely worth looking at, though it could be the CTIA, neither of which are that hard to come by, you can even do as I did and get a 2600 for spares (I thought I needed a RIOT).

@rubber_jonnie

Well I have tried a new riot chip and new cpu I dont have a ntsc tia but there is no change from the first photo the sockets were all bad so they are removed and I will put single row pin headers in then test again. It looks like I am on the hunt for a ntsc tia ic

Tom

Ready for testing
Again