Colecovision Board Revisions - Schematics

[Sirius]

Hi everyone, been awhile since I've posted here. I have a Colecovision pcb I've been trying to troubleshoot. The problem is, the board is an older version and the schematics...the only schematics...I've found seem to be for a later revision. The board revision is 75743 Rev C. The daughter board is revision 75745 Rev B. The console powers on, boots, plays and has sound but no display. Upon opening the console I found that someone had done some work to the daughter board in an attempt to repair it. The problem is every time I try to follow certain traces it leads to something else in the schematics or vice-verse. I've verified voltages are good, cleaned the power switch and tested for video on pin 36 of the VPU. Even if someone can post a picture of the section with the daughter card removed might be helpful. The best would be if there are schematics for this revision but I'm not holding out hope for that

 

Any help or advice would be great, thanks

[adamcon]

http://ann.hollowdreams.com/colfacts.html and download the 2nd from the bottom link............should have the diagrams you seek. From your description, I a concluding you have an ADAM. the colecoVision is only a single board while; while the ADAM is the computer bottom board and the cv game board as a daughter board containing the video/audio for the whole system. As a last resort, the F18A add on board bypasses the Coelco video/audio and replaces it.

[NIAD]

Think he means the CV PCB and the RF PCB.

[jltursan]

If we're talking about a CV and not an Adam, the "daughterboard" or RF board only implements an IC, the LM1889 encoder, under the RF board you can also find the analog switch, an HEF4066 IC. I've recently fixed a CV with a lot of faults that I slowly narrowed to something like you describe, clear B&W signal from VDP#36. In my case, both HEF4066 and LM1889 were faulty (!).

 

No idea about other mainboard revisions tho....have you traced the ouput of pin 36 to anything else?

[Ikrananka]

For the ColecoVision there is only one set of schematics that I have ever seen with one online source being here. However, as you point out these are for a Rev. H2 mainboard and a Rev. F RF daughterboard and so may well be different to your Rev C and Rev B boards.

 

The other caveat with these schematics is that they are riddled with errors and so cannot be totally relied upon even if your board revisions were to match.

Edited October 17, 2018 by Ikrananka

[atari-dna]

Do you have toggling on I/O Pin 35 on the VDP? Is the Color Burst clock present on pin 38? Are all CPU data lines active on the VDP? Pins 17-24 should be toggling as well.

 

Report back :0)