Atari Star Wars boards - Repair log

bakerhillpins

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In the process of repairing some spare sets of Star Wars boards that I eventually want to sell. So as I go through them I thought I would post up anything that I came across during the process.

Have a few sets I am going through so I figured I would start with the sound boards and once I get through those I would move on to the Main and AVGs one at a time to keep in the groove so to speak.

Rather than dump a bunch of debug into a single post I figure I will try to break posts logically in the hopes that it's a bit easier to follow where one board repair stops and the next begins.

First sound board was simple, replace a few missing components and it was up and working fine.
 
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The second Sound board:

I replaced the missing components and plugged it in. Right off the bat we had that wonderful smell of overheated IC. I didn't shut it down right away but rather put my hand on the board to figure out who was the culprit. Easy enough, the TL084 at 3A burned the s**h out of my finger so it was obviously the problem.

Cut out that chip and replaced it and plugged it back in. Scratchy/noisy sound but in the background music sounded clean/clear. Ran the sound test and it seemed that whenever speech was active the background noise got much worse so it was time to break out the O-scope.

The SW sound boards have several channels that are summed into a single amp (summing amp on sheet 16A) so it was rather easy to hit each channel with the O-scope to determine which one(s) were crap. Shooting through each it was evident that the crap was from the speech channel. The attached show my setup and the noise on the channel.
 

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I wondered if it was simply a bad TMS5220 Speech chip or something else. Substituting that chip into a known good board proved the chip to be good. So It's not that. Since executing the sound test on the board was successful (with the exception of speech), the board produced lots of good beeps when powered up with the self-test jumped, and all chips proved good in the working board it's on this board.

Because of the good beeps I didn't start with the address/data bus figuring something else would be bad. Rather I looked at the speech circuits. The Chip receives a clock signal so I started there. Probing that with the o-scope showed it looked nasty. Not a good square wave at all.
 

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Backing down the circuit, through the 4069 at 2H and to transistor at Q1 I noticed that the signal cleaned up on the back side of the 4069 as seen in the attached.

So I have cut out that chip and am awaiting a replacement.
 

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The final sound board:

This was complete but all the 100uf 35v the electrolytic capacitors had leaked. These are some odd light purplish ones that I rarely see on Atari boards. Most of them are the dark blue ones. I have never seen the dark blue ones leak. So off with these and new ones to be added to a cleaned board.
 

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