Need help with finding issue with Colecovision video output

[Leufion]

Hi all,

I've been trying to refurbish my Colecovision that's been in storage for a long time. I recapped it and installed the AV mod and saw that the graphics were still scrambled. I then desoldered the power switch, opened it up, gave it a good cleaning and applied Dielectric grease on the contacts before resoldering it back on. Once I did that the screen was black. I have a game that plays music after the Colecovision screen and I heard the audio clearly. I tried a lot of different things since then and I currently have video that is somewhat more scrambled than before. Here's all what I've done:

• Recapped using Console5's kit
• Installed AV mod using Console5's kit
• Bought and using a new 28.5 watt power supply
• Removed and replaced the VRAM and modded to use +5V with Console5's Memory Upgrade Kit
• Removed and replaced BIOS and modded to use Console5's Fast Boot BIOS
• Noticed C70 had a broken lead so I replaced it
• Replaced C106 in case the vertical lines were related

Any help would be appreciated. I've attached some pictures to the thread. I still hear the game sound and confirmed that the same video out issues are happening on a coax out as well as the composite cable.

 

[SYSTEMSQUIRREL]

Are you using a original power supply? If so it's not uncommon for the filter capacitors in the supply to fail which will cause graphical corruption.

Edited August 6, 2023 by SYSTEMSQUIRREL

[Leufion]

I am not using an original power supply - I bought the 28.5w Colecovision compatible one. I did notice the same issues using either old or new power supply.

[+mytek]

@Leufion possibly one or more of the Video DRAM chips is bad. Do the finger test to see if any are running hotter than the others.

[Leufion]

@mytek I didn't notice a difference in heat with the new VRAM chips. I did make sure all of the socket pins were soldered and none were pushed up.

[Leufion]

Tonight I retested the VRAM continuity and it appeared to be as expected. I then retested the voltage on Pins 1, 8 and 9 and noticed something odd with U16. The screen artifacts would change when I tested the pins on the one chip. The voltages read correctly, but I swapped U14 and U16 to see if it was an issue with the chip or socket. The chip in U14 was glitching out like it was when in the U16 socket so I am thinking I need a replacement.

[+mytek]

Somewhere there is a procedure written down on replacing the older VRAM which required multiple voltages with a newer variety that only needed +5V only. If you haven't already done so i would recommend doing this because the newer RAM is usually more reliable and runs cooler as well.

 

Found it: https://wiki.console5.com/wiki/Colecovision_/_ADAM_5V_RAM_Modification

 

[Leufion]

I used that wiki above when I installed that kit and I went through the troubleshooting section for testing the continuity and voltage. I replaced all RAM with new chips and replaced the DVC and heatsink with new ones as well. I reseat them, recleaned the switch and I'm still not getting a clear screen. I attached what the title screen and game screen have consistently looked like before and after replacing the chips, reseating and recleaning. 

[ChildOfCv]

Verify that the data line from each RAM chip really is making it to the correct pin on the VDP.  And only that pin.

[Leufion]

I got it! I had an incorrect VDC pin jumped to U14 pin 14. I had thought it was going to pin 31, but it was actually connected to VDC pin 10 which was directly above 31. Once I fixed that it was all working.

Thanks all for your help!