Need help with Coleco repair...

[3DOMan]

Me and a friend are trying to repair a Colecovision...it's difficult to pinpoint exactly what's causing the problem. The system does power on and read games, but it has nasty vertical white lines all over the screen, and the graphics come out all garbled and there's zero's all over the screen. We did a solder re-flow and a thorough cleaning on both the power switch and the cartridge connector, and it didn't seem to affect it. We also changed the capacitors, no effect. Any ideas?

[NIAD]

If you have an extra Power Supply, that would be a good next step. Otherwise, maybe a bad VDP or one or more of the Drams are bad... probably the Drams.

Edited March 14, 2013 by NIAD

[3DOMan]

What is the VDP? Thanks

[jetblue]

i am the friend! yes it is i,jetblue the technician that has fixed many of you guys consoles. we need help identifying this problem. heres some pictures:

 

 

 

 

 

this is space ace btw

 

thank you friends for looking. knowledge is free

Edited March 14, 2013 by jetblue

[NIAD]

What is the VDP? Thanks

It is short for Video Display Processor and the one used in the ColecoVision is a Texas Instruments TMS9928A (40 Pin DIP)

[+evg2000]

would that be a ram issue?

[NIAD]

after seeing those pictures, I would say you have one or more bad Dram chips. Anyway, I passed on info. on where in Chicago to get it fixed to 3DOman (Sean Kelly's store called VideoGames Then & Now) or you could always contact the resident CV Technician here on AtariAge, Yurkie, to have him repair the system if all else fails. Yurkie also offers a number of great Mods if you decide to have him repair your system.

 

BTW, the game name from the pics is Space Panic.

[3DOMan]

Thanks for the info...Judging from the pics, I would say the name of the game is SPACE SCRAMBLE

 

^.^

[NIAD]

would that be a ram issue?

Me thinks, but there could always be other possibilities. If the Power Switch was properly refurbished and the Power Supply checks out to be good (+5V, -5V, +12V) and the PCB is receiving the proper volts, then the next two logical items to consider are the VDP and Drams.

 

BTW, similar screen corruption is experienced with other cartridges? Also, try turning on the system without a cartridge inserted to see what the CV BIOS screen looks like.

[3DOMan]

The screen is also scrambled when using other games. We tried 8 different ones. It also is scrambled when using NO games, we tried that too.

[nanochess]

The screen is also scrambled when using other games. We tried 8 different ones. It also is scrambled when using NO games, we tried that too.

From what I can see, you should replace the DRAM connected to AD4 pin of TMS9918A (this is what changes a space 0x20 to a zero 0x30 and the vertical lines)

 

Anyway you should check first for continuity (with a multimeter) the data connection to DRAM, also signals RAS, CAS and R/W.

[Geoff Oltmans]

Yep... looks like a bad DRAM. The vertical stripes to me indicate that's probably just one bad one.

[jetblue]

finally was able to fix this. thanks guys for all the helpful advice that led me to the fix. this was fixed by changing the memory chips with the +5mod like the kit shown here:

http://www.arcadecom...687/7841035.htm

thanks to channelmaniac for replenishing his supply.

 

it was hard to remove the chips using desoldering braid and some pads around the chips were lifted but the holes the chip legs go into had metal in them so when the socket was soldered in there was contact.

hope this helps others with similiar problems.

Edited June 26, 2013 by jetblue

[+grips03]

finally was able to fix this. thanks guys for all the helpful advice that led me to the fix. this was fixed by changing the memory chips with the +5mod like the kit shown here:

http://www.arcadecom...687/7841035.htm

thanks to channelmaniac for replenishing his supply.

 

it was hard to remove the chips using desoldering braid and some pads around the chips were lifted but the holes the chip legs go into had metal in them so when the socket was soldered in there was contact.

hope this helps others with similiar problems.

 

 

Here is the process I use:

cut the legs of the chip

use tweezer nose pliers and solder iron to remove each leg one by one

then use flux on solder braid / board

then use solder braid with iron and don't move the iron / braid just wait

then solder in IC sockets

then clean area with flux remover and tooth brush and wash off with water

[atarian63]

just ordered this mod

[omgaz]

I had nearly the same garbled graphics. installed the 5v memory and now it works.. Thanks!

[zippiz]

I just bought a Colecovision from Ebay "as is", spend the day making a psu for it but when I turn it on the picture is just bars. I can hear the game starting, and I can connect a controller an start to play but the picture never changes at all.

 

So what do you guys think, might this also be a dram error? (I did check, and restored the power button).

 

 

[zippiz]

No one?

 

Will soon try to replace the RAM, did anybody try to cut the legs and just solder the ram on top of the old legs instead of desolder the chips?

[zippiz]

 

 

 

Working again!

[Rey]

Congrats!

[FABombjoy]

Will soon try to replace the RAM, did anybody try to cut the legs and just solder the ram on top of the old legs instead of desolder the chips?

It's ugly, but it works. I did it to my own CV to make sure - cut the chip bodies out, soldered sockets directly to the legs left behind.