5 replies to this topic

[mimo]

Trying to repair a dead colecovision,
So far I have removed and cleaned the power switch, replace PSU for a know good one, replaced DRAM at U15.
Still get a black screen on startup, sometimes with an audio screech.
Any ideas what I should do next?

[mimo]

edit, on some occasions with a cart inserted I get a blue border with blue vertical lines down the screen (Gorf cart) and with Donkey kong inserted I get a blue screen flash on every 3 seconds or so:x
once I got a garbled title screen on Gorf but I can't get that to happen again

[mimo]

another update, I get the same effect with nothing inserted at U15

[cybercylon]

mimo, on Tue Nov 17, 2009 6:40 AM, said:

another update, I get the same effect with nothing inserted at U15

One thing that often goes wrong is the RF unit (this sends the sound and video to your TV) inside the console. I had many video problems that were not caused by say the power switch. Eventually, I did an AV mod so I could catch the sound and video before it gets to the RF unit. There are many ways to do it. I used Ben Heck's AV mode because it is relatively simple, cheap, and my flat screen likes it. Everything has been working fine since. I can even move my console without it going haywire!

[mimo]

cybercylon, on Tue Nov 17, 2009 9:21 AM, said:

mimo, on Tue Nov 17, 2009 6:40 AM, said:

another update, I get the same effect with nothing inserted at U15

One thing that often goes wrong is the RF unit (this sends the sound and video to your TV) inside the console. I had many video problems that were not caused by say the power switch. Eventually, I did an AV mod so I could catch the sound and video before it gets to the RF unit. There are many ways to do it. I used Ben Heck's AV mode because it is relatively simple, cheap, and my flat screen likes it. Everything has been working fine since. I can even move my console without it going haywire!

I should have mentioned that it is a PAL system, unfortunately the AV mods do not work on these. I don't believe the problem to be RF related as when I do get any output on the screen the signal is good and strong.

[channelmaniac]

mimo, on Tue Nov 17, 2009 5:53 AM, said:

once I got a garbled title screen on Gorf but I can't get that to happen again

Sounds like bad DRAM. Do the modification on the board and replace those pesky 4116 DRAMs with some 4516 or 4164 types that are 5v only.

http://newlifegames....g11121#msg11121