What could be wrong with my new ColecoVision?

[cbmeeks]

So I bought two CV's off eBay for <$20 each. Both were reported not working.

 

I managed to clean and mod the first one and it works like a champ.

 

However, my second one isn't working correctly. My suspicion is bad memory. The unit powers up, the audio sounds fine but the screen is all messed up.

 

But, it's messed up in a "bad data" type of way. For example, instead of saying "GET READY PLAYER 1" it says "GEP REAWY PCAYER 1". The game select screen says "PPRQQ @UTTML ML IEYPAD"...etc.

 

(screen shots attached).

 

So, what are your thoughts? I've cleaned it up physically. In fact, this was one of the cleanest units I've ever seen. Looks almost mint besides a little dust.

 

All of the electrolytic capacitors are fine. Well, they aren't bulging and there is no leakage.

 

I didn't take the RF unit apart to see if anything was leaking under it but I don't think that is the issue anyway since it isn't a bad picture for RF. Just looks like the letters have been replaced, colors swapped, etc.

 

Thanks.

Edited April 20, 2015 by cbmeeks

[NIAD]

If the Power Switch has been cleaned and repacked with dielectric grease, then the issue you are experienced is due to one or more bad Ram chips. Head over to http://ann.hollowdreams.com and download the CV Technical Manual for details as to which RAM chip(s) might be the culprit.

[nanochess]

Yep, it looks like a VRAM memory failure. One of the eight chips is faulty.

 

I don't see clearly which one.

[NIAD]

When posting pics of issues with the CV, especially when you think it's a RAM issue, it's best to just use the CV BIOS screen (ie: no cartridge inserted).

[Kiwi]

Probably bad vram. Probably memory range $1800-$2000, which holds the screen data, and sprite tables have gone bad.

[cbmeeks]

Yeah, I was afraid of that. I might look into possibly replacing with SRAM. Of course that would be a major mod.

[VectorGamer]

Is this fixable? I have a CV that may have the same issue and want to know if it's possible to have it repaired.

[NIAD]

Is this fixable? I have a CV that may have the same issue and want to know if it's possible to have it repaired.

If you are not comfortable desoldering the old chips and then soldering new sockets in place for the repacement chips, then Yurkie is the man to contact.

[Vectorman]

Try a different power supply before you go desoldering memory chips/power switches. CV's are very picky about PS's and sometimes work perfectly with one and are glitchy with another.

[cbmeeks]

I only have one power supply. But it's confirmed working.

 

Anyone know of any SRAM replacement mods?

[NIAD]

I only have one power supply. But it's confirmed working.

 

Anyone know of any SRAM replacement mods?

http://www.arcadecomponents.com/index.html

 

The F18A VGA Video Upgrade also replaces the built-in RAM of the CV:

 

http://codehackcreate.com/archives/335

[CrazyBoss]

its something with bit 1 ?

bit 1= 2 decimal.

 

S is shown as Q

2 is shown as 0

K is shown as I

 

what is common for those is if you take the ascii value of the lette should be shown, and set bit 1 to 0, (minus 2 if you want), then you get

what is show on the screen.

 

But not sure what its is cause if the vram was bad bit 1 always=zero, then i would suspect sprites and letters and other graphics to be

bad too.

[Vectorman]

This kind of crap is why we need that CV 1.2 project now more than ever. All the CV's out there are probably toast by now. I considered buying another CV off ebay but I'm too tired of dealing with these problems.

[NIAD]

This kind of crap is why we need that CV 1.2 project now more than ever. All the CV's out there are probably toast by now. I considered buying another CV off ebay but I'm too tired of dealing with these problems.

Then you should buy an ADAM.

[cbmeeks]

I have an ADAM. Love it. But the damn thing takes up half my office. Lol.

 

My dream is to build my own "CV1.2" like console. It would be driven by a propeller for video and other things with a real Z80. Just need to get off my butt and build it. Lol

[Pixelboy]

My dream is to build my own "CV1.2" like console. It would be driven by a propeller for video and other things with a real Z80. Just need to get off my butt and build it. Lol

So we're talking about something like this?

 

[cbmeeks]

Bingo. It would be that exactly.

[jackrabbitslim13]

My colecovision does the same thing, missing letters at the start screen and garbled graphics, but the expansion module 1 (Atari games) works great. I've cleaned and greased the power switch, so does that mean I have a bad chip?

[Yurkie]

You guys are welcome to send your console for repair send me a pm.

[cbmeeks]

I think I have identified two bad 4116 RAM IC's that I hope to replace tomorrow. Thanks.