Coco3 problems

[MarkO]

On 6/21/2022 at 4:29 PM, hhos said:

Disclaimer:

I'm afraid I remembered incorrectly about that cap, C65.  It is not a decoupling cap, and it is on the RAS/ signal from the GIME.  C66 is not mentioned in the conversion procedure in my tech manual.

 

<< BIG SNIP >>

This is the Install Manual for the PBJ 512KB Memory Board with 41256-12 DRAMs.  Both C65 and C66 are mentioned and removed when upgrading:
https://colorcomputerarchive.com/repo/Documents/Manuals/Hardware/PBJ 512cc Memory Upgrade Board (PBJ).pdf

 

The Triad from Cloud-9 and the Boomerang, eventually from me require the removal of C65 and C66.

 

MarkO

[jham55]

All is well in the world. It was bad ram. thanks everyone.

[hhos]

How many were actually bad?

[jham55]

I bought 25 and replaced all of them so not sure 

[MrDave]

Ram is the hardest working chip in these machines..runs the hottest...wearing out after 35 years in not a big supprise..

[hhos]

On 6/28/2022 at 3:36 PM, jham55 said:

I bought 25 and replaced all of them so not sure 

It is highly unlikely that all of them are bad, so don't throw them away please. If you don't want them send them to me.

 

9 hours ago, MrDave said:

Ram is the hardest working chip in these machines..runs the hottest...wearing out after 35 years in not a big supprise..

I don't agree. The CPU, bus management, and the Video processor frequently run hotter, sometimes requiring heat sinks.  In any case there is probably only one bad chip in the lot unless it's been abused.  Throwing away RAM is a practice reserved for SIMMs, DIMMs, etc.

 

[vintagegamecrazy]

So hopefully threadjacking is better than a new thread. I have some issues with my Coco 3 as well. I have no problem doing repairs but am not great at diagnosis so here goes with the questions. I've played a few different games just today, haven't used the computer in a year or two before this and noticed that sometimes games boot in black and white. It happened with Skiing, a Coco 1 game and then had color after a few resets. Robocop is always black and white and I played Arkanoid and any letter M is corrupted in the game. Also what's with Arkanoid having a jittery Vaus no matter what joystick I use?

 

The video is also ripply, is this bad capacitors? I can do the caps no problem if so. Are the other issues bad ram? If so is it best to replace all and I also want to upgrade to 512k for sure.

 

Any help is appreciated.

[eightbit]

3 hours ago, vintagegamecrazy said:

So hopefully threadjacking is better than a new thread. I have some issues with my Coco 3 as well. I have no problem doing repairs but am not great at diagnosis so here goes with the questions. I've played a few different games just today, haven't used the computer in a year or two before this and noticed that sometimes games boot in black and white. It happened with Skiing, a Coco 1 game and then had color after a few resets. Robocop is always black and white and I played Arkanoid and any letter M is corrupted in the game. Also what's with Arkanoid having a jittery Vaus no matter what joystick I use?

 

The video is also ripply, is this bad capacitors? I can do the caps no problem if so. Are the other issues bad ram? If so is it best to replace all and I also want to upgrade to 512k for sure.

 

Any help is appreciated.

 

It was a 1 year old hijacking for sure

 

I won't try to be an expert on the CoCo 3 but I will say that I have used Cloud 9's services for repair over the years and they have never failed me:

 

http://www.cloud9tech.com/

 

[hhos]

The first thing to do is clean out all the dust, if any, so we won't be chasing some silly fuzzball. Assuming that doesn't fix it I need to understand what is meant by "ripply".  Does this mean that the video has a slow-moving wave traveling vertically through it?  For now, given the other symptoms you describe, I'll assume not.  I will also assume that you can't measure the clock frequency going out to the CPU.  Intermittent and/or constant B&W might indicate the color burst signal in the video is not being detected.  It's intermittent so hopefully tweaking TC1 a bit will be an adequate solution.  Before adjusting it note its starting "home" position.  If it's turned all the way to either end it's probably been maladjusted and it's unlikely that we will want to return it to that position, but remember where it was.  I can't read this PCB layout very well, but I think I see TC1 under the right end of the keyboard connector.  There are two resistors between the KB connector and the trimmer capacitor, TC1.  If you have a small, non-metallic screwdriver to adjust it, use that.  Otherwise, just use what you have.  A metallic tool may effect the frequency just by contact with the cap. which will make it harder to do, but I've done it many, many times.  

 

  If you run into any snags, or it just flat doesn't work, let me know.  I'll dig out a CoCo3 so I can see what I'm talking about.

[vintagegamecrazy]

I basically get horizontal RF noise through it even though it's on composite input. It seems to be the capacitors getting worn out. I am getting the jitter on most games that support analog controllers. It did it on arkanoid and now Polaris. Does anybody know what causes that? Also if the ram is failing will upgrading it to a 512 k RAM upgrade fix the bad ram or is there additional RAM chips besides that upgrade that have to be replaced?

 

Once again I have plenty of good at soldering equipment I do a lot of repairs on game systems but I have no experience with the TRS-80 or troubleshooting with it. This is where I will need the advice from.

[hhos]

What does it do if you boot into BASIC?