Intermittent Turbo Duo CD reading

bigjoeroy · 12/06/2011, 09:42 AM

Hello,

I've been working on a Duo for a friend and have run into a frustrating issue. Sometimes it will read discs and other times it won't. Usually once its working its fine, but after its turned off the next day it will not read discs again. The disc spins but the game won't load.

here's whats been done to it so far:

1. Replace all electrolytic caps (to fix audio problem)
2. Tweaked the pots
3. Replaced laser assembly
4. Tweaked the pots
5. Replaced laser assembly again (first replacement appeared to be used)
6. Tweaked the pots
7. Wiggled wires going to laser assembly while it was operating correctly to look for intermittents. (none found)

Unfortunately I don't know if it had the issue before I replaced the caps.

Does anyone have any ideas on what else to try?

thanks

HercTNT · 12/06/2011, 10:31 AM

I recommend contacting thesteve in these forums. He has done some repair work for me lately and is fixing a duo for a friend of mine. I"m sure he will be able to help.

Keith Courage · 12/06/2011, 12:01 PM

Did you replace all the caps on the board or just the audio ones? There are some by the CD drive that handle the power for it. Also double check closely to make sure that one didn't accidentally get installed backwards somewhere.

nat · 12/06/2011, 08:09 PM

This reeks of a cap problem.

Issues that have anything to do with "doesn't work cold, but works when it warms up" usually = caps.

bigjoeroy · 12/06/2011, 10:30 PM

Thanks for all the responses. Yes, I did replace all the electrolytic caps on the board.

I also think it might still be a cap problem. There is a ceramic cap on the board that I can put my finger on when its not working and it will make it work (circled in red on attached image. I'll have to check for the designator tomorrow). I put a scope on the non-ground side and it measures around 2.5V and is pretty noisy (at least 100mV noise).

nat · 12/06/2011, 10:42 PM

Did you wash the board after the cap change? If not, you could (probably are) dealing with electrolytic residue from the old caps wreaking havoc with things.

A normal (non-drying) cycle through the dishwasher usually takes care of it.

You should *always* wash a board after a cap change. If you don't, you are almost guaranteed further problems.

If you've already done this, replace that sucker.

bigjoeroy · 12/07/2011, 02:25 PM

I only did spot cleaning with flux remover when I changed the caps so I'm sure it could use a thorough cleaning, although my friend is a bit uneasy about the dishwasher.

I checked it some more today and it is actually attaching my scope's ground clip (or any other earth ground) to the board that makes it work. That should be a good clue, but i don't know what.

thesteve · 12/07/2011, 03:06 PM

i am 99% sure you dont have another earth ground connected during testing.
IF the ground makes it run then touching the AV jacks shell to ground will work too.
what i found causing intermittent read issues (tracking errors) especially cold is binding in the laser sled due to dirt or dry grease.
that cap will be hard to identify, but if defective should be replaced.

nat · 12/07/2011, 07:22 PM

Quote from: bigjoeroy on 12/07/2011, 02:25 PMI only did spot cleaning with flux remover when I changed the caps so I'm sure it could use a thorough cleaning, although my friend is a bit uneasy about the dishwasher.

That's completely ridiculous.

Explain to your friend that ALL PCBs go through a wash cycle, much harsher than a standard dishwasher cycle, at the factory.

bigjoeroy · 12/08/2011, 01:29 PM

Quote from: thesteve on 12/07/2011, 03:06 PMi am 99% sure you dont have another earth ground connected during testing.
IF the ground makes it run then touching the AV jacks shell to ground will work too.
what i found causing intermittent read issues (tracking errors) especially cold is binding in the laser sled due to dirt or dry grease.
that cap will be hard to identify, but if defective should be replaced.

I don't understand your comment about the earth ground. All I was saying that if I connect earth ground to board ground it seems to work correctly. If only the TV or AC adapter was connected to earth ground everything would be OK.

I'm pretty sure its not binding of the laser sled because it seems to run smoothly thoughout the full range if I turn the motor manually. Also attaching an earth ground would not affect a binding problem. How would I know if it was binding during operation?

I also have reflowed all the caps on the CD drive end of the board and gave the board a thorough cleaning and it is behaving exactly the same.

I was probing the electrolytic caps for noise and noticed a 200mV 120Hz signal on the two through-hole caps C136 and C163 near the BA chips. I'm not sure if this is normal or not.

thanks,
Joe

Arkhan Asylum · 12/08/2011, 02:14 PM

As far as washing boards go:

my standard Amiga 2000/2500/3000/4000 washing pattern is to lean it against my garage and blast it with the garden hose.

So, your dishwasher won't do anything to it.

thesteve · 12/09/2011, 12:05 AM

120Hz sounds like a prob 200mV is just below trouble threshold for most logic functions.

my earth ground comment was because if the unit doesnt have a current path to ground, adding one shouldnt effect it.
on the other hand if it is connected to more than one ground referenced devices that have an AC potential between them it will drive it nuts.
often connecting a good ground in this case will improve things.

try checking for ripple on the ac adaptor and the tv to ground referance.