Colecovision VRAM Fail help

[Yurkie]

I was wondering if one of you knowledgeable repair guys could tell me what this error means?

 

I was running the USB cartridge diagnostic on my 128-1 multi-cart. I get this message when I select VRAM test

 

VRAM Test FAIL @ 0x7194 [71,F7]

 

When I run the Final Test Cartridge that is also loaded on the multi-cart it goes through all the way with no problems.

 

I put the Donkey Kong Cartridge in and ever thing looks good on the splash screen except there are a few black pixels on the bottom of C the O and the C in the word colecovision and the n in Donkey Kong is the letter f. aside from that everything looks good. When I try another cartridge, or roms on my multi-cart the pixels are always missing from the CO and C like I mentioned above. All I have noticed during game play is a few pixels being black. I would have done screen shots but digital camera battery is dead.

 

I was hoping if I check the RF box for broken solder joints, rebuild the power switch and clean the cartridge slot this would be a great working colecovision. I had to go and test it and bum myself out. Could the things above cause a false positive? I know the power supply and rf cables are good, they are the ones I use for the system I play all the time.

 

Any help is much appreciated.

Edited July 14, 2009 by yurkie

[doubledown]

Todd, your best bet is always going to be to use a logic probe and test each of the VRAM chips individually.

[Yurkie]

Does the error code point to a specific VRAM IC being bad.

 

I think if such a diagnostic rom exists, shouldn't the code generated point to a specific IC.

 

If not what good is the diagnostic rom?

 

 

 

 

 

I do appreciate your response doubledown

[newcoleco]

I'm not an expert and I'm not the one who program the vram test utility.

You should visit the Atarimax forum and talk about your vram test result.

[Yurkie]

I'm not an expert and I'm not the one who program the vram test utility.

You should visit the Atarimax forum and talk about your vram test result.

 

Thank You, I was not aware that there was a forum.

[Yurkie]

I'm not an expert and I'm not the one who program the vram test utility.

You should visit the Atarimax forum and talk about your vram test result.

 

Thank You, I was not aware that there was a forum.

[doubledown]

I have seen the CV Multi-Cart's built-in VRAM test fail when all VRAM ICs are fine, but the VDP is not working properly. There was a topic about this previously where Steve did explain what the VRAM failure code represented.

[Yurkie]

I have seen the CV Multi-Cart's built-in VRAM test fail when all VRAM ICs are fine, but the VDP is not working properly. There was a topic about this previously where Steve did explain what the VRAM failure code represented.

 

 

That's intersting. Would it be possible with an eprom burner to dump the code from the VDP, them burn this to a eprom replacement IC. I ask this because from everything I have read it seem that the VDP is very hard to come by, and I assume expensive also.

[marc.hull]

I was wondering if one of you knowledgeable repair guys could tell me what this error means?

 

I was running the USB cartridge diagnostic on my 128-1 multi-cart. I get this message when I select VRAM test

 

VRAM Test FAIL @ 0x7194 [71,F7]

 

When I run the Final Test Cartridge that is also loaded on the multi-cart it goes through all the way with no problems.

 

I put the Donkey Kong Cartridge in and ever thing looks good on the splash screen except there are a few black pixels on the bottom of C the O and the C in the word colecovision and the n in Donkey Kong is the letter f. aside from that everything looks good. When I try another cartridge, or roms on my multi-cart the pixels are always missing from the CO and C like I mentioned above. All I have noticed during game play is a few pixels being black. I would have done screen shots but digital camera battery is dead.

 

I was hoping if I check the RF box for broken solder joints, rebuild the power switch and clean the cartridge slot this would be a great working colecovision. I had to go and test it and bum myself out. Could the things above cause a false positive? I know the power supply and rf cables are good, they are the ones I use for the system I play all the time.

 

Any help is much appreciated.

 

 

 

 

I'll preface this by saying that my experience comes directly from TI99 hacking (But both use the same VDP...(or variation of...))

 

It sounds like your DRAM used by the VDP has some holes in it and is dropping bits. It is fairly easy to isolate which IC it is by simply Piggy Backing a 4116 on the back of the soldered in ones (make sure the orientation is correct) until the problem is corrected. No need to solder them on as a tight friction fit will work. When the IC is isolated a quick pull and plug will fix the problem.

[Yurkie]

 

 

 

 

I'll preface this by saying that my experience comes directly from TI99 hacking (But both use the same VDP...(or variation of...))

 

It sounds like your DRAM used by the VDP has some holes in it and is dropping bits. It is fairly easy to isolate which IC it is by simply Piggy Backing a 4116 on the back of the soldered in ones (make sure the orientation is correct) until the problem is corrected. No need to solder them on as a tight friction fit will work. When the IC is isolated a quick pull and plug will fix the problem.

 

 

That's very interesting. You have did this on a colecovision?