Here's the manual to get you started, schematics towards the end: https://www.ipdb.org/files/126/Data_East_1990_Back_to_the_Future_Manual.pdf

So if you really want to dive into fixing this, the first thing I would do is to measure the current going into the IC. Yes...easier said than done, but that will give you a big answer about heat. According to the data sheet, it should be 80 to 200mA w/no audio. 12V x 0.2A = 2.4W. That's how much power it dissipates just sitting there, worse case.

For now, let assume the power supply is not an issue since you tried two. And for now, let's also assume the circuitry driving the 3730 is OK, but could be the culprit too - but one thing at a time.

Also look at C3 (or whatever it is on your specific IC you're focusing on). That keeps the amp from oscillating, according to Fujitsu. It could be oscillating and you would never hear it, but it could be going full bore w/o you even realizing it. Ironically, it looks like DE used a 0.15uF, whereas Fujitsu shows what appears to be a 1uF. Check C2 and C4 too. Just guessing those provide a high(er) frequency termination. Just a WAG, but that might also lead to an instability too. Fujitsu recommended a mylar cap. C14, if leaky, could be causing a DC offset. I wouldn't discount that either.

Another simple thing, but very important - clean up the heatsink and apply new thermal grease. Not much, just a thin layer. That helps wick away heat from the IC into the heatsink. Is the heatsink soldered to the board (I don't have a clue if it should be). If it is, check those solder joints too because the heatsink will xfer the heat into the board (usually a bunch of ground plane). The amp could be fine, but if the heat has no place to go - then that is an issue.

Hope this helps. Not much to wrong w/the chip - not a lot of parts involved. Just looks like high power op-amps. But I tossed out a lot of comments, hopefully you can start to narrow it down.

here's a link to the 3730 data sheet: https://www.datasheetarchive.com/pdf/download.php?id=3bb4dd06dc8fa38fc4bd4c8a5c4e0e19205382&type=M&term=mb3730

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What test equipment do you have, just a multi-meter?

As Razor mentioned, did you check the polarity of the caps? The C3 I mentioned above, did you replace that by chance? Was there thermal grease on the heatsink?

Mind posting some pictures of the area in question, both sides of the board? Lots of people here willing to help, someone might spot the issue right away.

On the bright side, things should be fairly straight forward. You just need to eliminate one thing at a time and move on to the next possible culprit.

Thanks for the pics, wont be able to take a close look until tomorrow.

Asking the obvious again, heatsink compound on the IC? We really need to know this before anything else. Ideally, new.

What about the c3 cap? Was that ever replaced?

A word about solder: The lead free you can buy at Wallymart is somewhat hard to deal with since it has a higher melting point. Some decent 63/37 or 60/40 that contains lead is a lot easier for a newbie. Rosin core too. Don't use plumbers solder, not safe for electronics long term.

Where's C27 on the schematic? I searched for it, but didn't see it.

Jim,

Ahh...OK. I was looking at my LAH schematic which is a little different. Hitting the sack now, will look at it Monday night.

Did you by chance mention what pin this is for? Apologies if I missed it.

Thanks.

Jim,

Duh, senior moment for me. Back at the beginning of the thread, I even posted the link to the game manual at ipdb.com. LOL!

So rather than having you buy a bunch of parts and replacing all the possible culprits one at a time by educated guesses, consider getting one of these and just test what's in the game. Granted you'll likely have to remove parts to test. It really is slick for $20. Get some decent solderwick, and it won't be that bad. Food for thought.

ebay.com link: B1 Color 1 8 TFT ESR Transistor Resistor Diode Capacitor Mosfet Tester w hook

C27 - yes, that's the C3 in my LAH. If could be bad, but it won't leak tho.

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No doubt, can be hard to chase down an intermittent. I guess keep an eye on it for now. At least you sort of have an idea when it's acting up w/the crackling noise being a indication.

Hang in there, it will seem like a wild goose chase - but it's a process of elimination. Lot's of people here willing to help.

Don't forget the earlier post I did about the parts tester...cheap $20 investment.

Good deal. Still might be hard to spot an intermittent part, but that's a good start.

Let us know when you get it and start to test parts.

Caps are cheap, easy enough to shot gun it and replace them all and keep your fingers crossed.

Shipping is probably just as much as the caps.

That cap is polarized, so there is some sort of marking. Keep in mind sometimes the marking is for the +, other times it for the -.

Edit: Oops, didn't know that was you Grumpy posting and not the OP. Apologies.

Just asking the obvious... I assume there's no screws here because you were tinkering w/the board, right?

Sorry - had to ask.

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Just checking in, been awhile. Any progress?

Jim,

Stumbled back on this post and didn't see any activity, thought I would 'ping' you.

Good deal it's working. One other thing you can put in your arsenal if ever needed is a can of freeze spray. Really helps spotting intermittent parts, especially if it's heat related (doesn't sound like yours is).