CoCo Repair, Identify IC?

[bug2k17]

I'm trying to fix a fault on my Color Computer, I broke this over 30 years ago while playing with a diy cartridge slot board. I put it to one side and never got round to fixing it. It now powers up and show random characters on screen, but no prompt. I'm just trying to work out the power line requirements for the major chips. Are schematics available for this version of the board?

 

I have now socketed all the ICs on the board. As I have a Dragon 32, which uses mostly the same chips, I have swapped out most of the ICs in to the Dragon and seem to work fine, such as the cpu, 74ls783, 6821, 6822, 6847, 74ls138, 74ls273, 74ls244. I also have 2 sets of working ram chips which do not seem to make any difference.

 

I have checked the power and ground to all ICs and they are fine, with the exception of one chip for which I cannot find the datasheet, I have attached a picture if anyone can help on where to look.

 

 

 

 

Thanks.

 

 

[Keatah]

What's the model # of the computer? 26-3004?

 

Is it a PAL version with extended basic? Or NTSC 64K + extended basic?

Edited September 6, 2017 by Keatah

[bug2k17]

The model is a 26-3003. This is a UK PAL version with 32k (uses 8 64k x 1bit memory chips) with Extended Basic.

 

Thanks.

Edited September 7, 2017 by bug2k17

[MarkO]

The model is a 26-3003. This is a UK PAL version with 32k (uses 8 64k x 1bit memory chips) with Extended Basic.

 

Thanks.

 

I am not seeing a Technical Manual in here for the CoCo 1 PAL...

 

Are you a member of the TRS-80 CoCo Facebook Group or on the CoCo Mailing List???

 

 

 

MarkO

[bug2k17]

I am not seeing a Technical Manual in here for the CoCo 1 PAL...

 

Are you a member of the TRS-80 CoCo Facebook Group or on the CoCo Mailing List???

 

 

 

MarkO

 

Thanks Mark, yes I have tried on the Facebook page, but nothing new has come from that.

 

I will join the list and see if any further information is available there.

 

I have seen that Dave Jones at EEVBlog has just taken what looks to be a PAL Coco1 apart in a recent video, but no new information on it. I see that the chip on his board has a different number to the one above I am looking for. I might drop him a msg and see if he knows anything more on it.

[MarkO]

Thanks Mark, yes I have tried on the Facebook page, but nothing new has come from that.

 

I will join the list and see if any further information is available there.

 

I have seen that Dave Jones at EEVBlog has just taken what looks to be a PAL Coco1 apart in a recent video, but no new information on it. I see that the chip on his board has a different number to the one above I am looking for. I might drop him a msg and see if he knows anything more on it.

Having a Schematic would give you an idea of what the chip is used for... I have a Rev-D 4K CoCo 1, NTSC, I can look as see if it has a similar chip...

 

MarkO

[Waltermixxx]

Home made cartridge slot... i would think perhaps a burned out track on the bottom of the board... seeing as all the replacement chips worked on the other computer, I'm guessing that perhaps the reset circuit may also be affected, seems like it's not resetting... when you do find a schematic, have a look at the reset circuit... it might help?

 

hope this is helpful

[bug2k17]

Thanks for the help. I have checked visually and cannot see any broken or burnt tracks. The reset button appears to work correctly, I'll check the signal to the cpu later just to make sure. I have put a scope on the IC pins suggested in the SAMS diagnostic pdf and they seem correct.