Fixed - Tron sound question - Which LS191 chip is which channel?

CaptainHendry

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Fixed - Tron sound question - Which LS191 chip is which channel?

I've been working on getting my Tron working. So far I've fixed fuses, added a switching power supply from Arcadeshop, capped and adjusted the monitor and capped the audio amp board. But I still have problems.

- Sometimes I'm missing channel 5 and sometimes I'm missing 4,5, and 6.
- Sounds are barely audible in attract mode.
- Some sounds are missing (maybe because they are on channel 5).

My first guess is that the LS191 for channel 5 is dead since that channel never works. I'd like to replace that chip instead of shotgunning all six.

The schematic shows six 74LS191 chips, one for each of the 6 channels but I can't find anything on KLOV which says which is which. Does anyone know which chip is channel 5?

I also have replacement 4016s. If I knew which channel was #5 I could replace the 4016 in that chain as well.

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Looks like you got the answer but what I've done in the past on stuff like this is, you can snip one leg on the 1uf capacitor at the end of each channel and see which channel you just lost. Then solder it back and try the next one.
 
Looks like you got the answer but what I've done in the past on stuff like this is, you can snip one leg on the 1uf capacitor at the end of each channel and see which channel you just lost. Then solder it back and try the next one.

It's easier to lift the leg of the resistor, and they're a lot cheaper if you break them :)
 
That's true... if the cap is down on the board like it should be too it'd probably be harder to get one side up without pulling it apart....
 
Socketed and replaced the LS191 at F4 and no change. Channel 5 is still missing. Replaced the 8910 on that side of the board. No change.

So at this point should I be looking at any particular 4016 or just replace all of them? Is there something else to check?
 
Replaced the 4016 at D8 and I'm still missing channel 5.

The channel test runs through each channel from 1-6 over and over until you stop it. At first channels 4 and 6 are faint and 5 is absent. After 4-5 times through the sequence channels 4,5, and 6 are all missing, 4 and 6 fade out. I repeated this twice and got the same result.

Tried touching some of the chips while it was running to see if I could identify a hot one. Everything was cool to the touch except D11, which is a 74190 up/down counter. I have no idea what D11 does in the circuit but should it be warm after 2-3 minutes? Could it result in channels 4-6 fading out as it heats up?

Here it is in the schematic. Any help would be appreciated:

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Basically the only ICs left in the channel are a 7407 buffer, a LM3403 op amp and LM3900 op amp. You should be able to verify the buffer easily with a logic probe while the channel test is looping (or a logic comparator). Since the other 2 channels also go out, maybe one of the op amps is most likely. If you have a scope you could verify them before pulling.
EDIT: you can ignore the LM3900, since it amplifies ch 4,5 & 6 mixed together
 
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Basically the only ICs left in the channel are a 7407 buffer, a LM3403 op amp and LM3900 op amp. You should be able to verify the buffer easily with a logic probe while the channel test is looping (or a logic comparator). Since the other 2 channels also go out, maybe one of the op amps is most likely. If you have a scope you could verify them before pulling.
EDIT: you can ignore the LM3900, since it amplifies ch 4,5 & 6 mixed together

Okay, so I'm looking at C10 and possibly also C6. I'll order those.
 
I have both of those if you're in a hurry and can make the drive out.

Appreciate the offer. I was just passing through (twice) on Saturday. But I'm not in a big hurry and I ordered both chips from Mouser last night so they should be here by Thurs.

Tonight I tried verifying that I don't have a problem on the audio amp board by jumpering the right lead (channels 4,5,6) to the left side of the amp. For some reason I could not get it to work. I jumped the R audio, V audio and V return which is connected to the R shield on the board but I could never get anything, not even static.

Plugged the connector back in and I had everything but channel 5 for a while, so I know the right channel is at least partly working. Hopefully those chips will solve my problem.
 
Success! I replaced C10 and C6 on the audio board, which were the only chips left in the channel 5 path. Now I have all channels working.

At first, channels 4-6 were a little quieter, then I remembered I had replaced the 8910 chip on that side of the board with a chip that wasn't a match. I put the old 8910 back in and now the sound is even all around.

This weekend I'll be stripping the cab to prep it for paint. If I can get an order in for a Phoenix art kit, I might have it all back together by Halloween.

Thanks to everyone who helped me out in this thread.

 
Do you have a TTL tester? I'm curious if it was the 7407 or LM3403.

No, I don't have one. I've thought about buying a cheap one off eBay but wasn't sure about the quality. Do you have a recommendation?

I could have replaced them one at a time but I had everything out and also replaced all 10 electrolytic caps on all 3 boards, so I just did both at once.
 
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