R-Type LEO sound problem

[NFGx]

I have an original R-Type LEO board that I recently plugged in, and found that it has a sound problem. First, a description of the problem, then a list of the things I've tried. I'd appreciate any clues or suggestions.

The Problem

Initially, the sound of launching the bits, running out of bit energy, and re-homing the bits was completely missing, and the blue laser had some speech sample instead of the pzeer pzeer laser sounds. After I removed and re-socketed every EPROM, this changed.

Next, 'three two one let's go' became 'three two oh'. The blue laser sound was fixed, and the bit send/retrieve was weird but it worked, more or less. The music tended to be a bit odd sounding.
After poking and flexing the board, I was occasionally able to make it change a little bit (three two one let's-) but for the most part the changes are stable. After a few dozen reboots and attempts to find the problem, it's stopped changing and it's basically stuck on 'weird'.

What I tried

• I pulled every EPROM and verified the contents on an EPROM reader.
• I pushed and pulled on the board everywhere I could
• I pushed on the pins of what I assume are the music chips (the big Yamaha and the 80-pin next to it)
• I brushed and scrubbed every socketed chip, pins and sockets
• I brushed the big PCB interconnects, moved them around, half-seated them, in an attempt to make them connect slightly differently
• I adjusted the voltage, from ~4.96 - 5.1V and back again.
• I carefully examined the board at the base of every component on the ROM board and the sound section of the CPU board.
• I doubt it's relevant but I also re-capped the board a couple of years ago.

The sound test plays the FM music weirdly. It's drum heavy. The AD sound test -seems- OK.

tl;dr - Most of the sounds play, but some are wrong. They changed once or twice after physically abusing the board while troubleshooting. It's otherwise stable.

Any ideas?

 

[Starcade]

Could be a dry joint somewhere. Flexing the board often establishes the connection lost through the dry joint. Continued flexing of the board may have permanently lost the ability to bridge the dry joint so it now remains in its odd state.

These boards are known for bad capacitors in the sound section. Bass heavy beats is often a symptom of failing capacitors. Changing the capacitors can make a big difference on these boards but it sounds like you have more than faulty capacitors in there.

 

[NFGx]

It's not like it's just louder, I guess it's more obvious because it's totally out of sync with the rest of the music. Here's an .m4a recording. (~1 minute, 1.3MB)

I agree that it sounds like a failed solder joint somewhere. I was hoping for either some idea where or some idea how to find it. I did try to re-flow the legs of the music chip but haha I am not skilled enough to do that without making it worse. Those pins are SMALL.

 

[ShootTheCore]

As a test, try flashing fresh sound EPROMs, install them in place of the originals, and see if the problem clears up. If it does, swap back each original sound EPROM one at a time until the problem comes back and you’ll know your culprit.

It is possible for an EPROM to fail in such a way that it reads out data fine with a programmer but not on a running board. The programmer reads the ROM data out sequentially once while a running game reads from the ROMs all over the place continually, and sometimes a failed ROM can’t handle the heavier demand of the latter scenario.

Looks like the sound ROMs are IC14 and IC17. You’ll want to use 27C512 EPROMs.

 

[AlxUnderBase]

No offence : https://www.arcade-projects.com/forums/introductions.56/

 

[NFGx]

As a test, try flashing fresh sound EPROMs, install them in place of the originals, and see if the problem clears up. If it does, swap back each original sound EPROM one at a time until the problem comes back and you’ll know your culprit.

I happened to have a couple of 27C512s lying around, and we can strike this as a possible cause. With the new chips installed the problem was unchanged.

 

[ShootTheCore]

Drat. OK, let’s try another EPROM. PCM data is stored in the ROM at IC8. Try swapping it out for a programmed EPROM. The MAME file name is rtl-da.bin and you’ll use a 27C040 EPROM.

 

[NFGx]

I have thrown in a new PCM chip, and like has happened before for unknown reasons, things changed a little bit.

Now instead of 'three two oh' it goes 'three two one" with the slightest tish at the end. But it's still way off with the music sync.

 

[ShootTheCore]

Interesting. Since changing that EPROM affected things, check the traces on the underside around that socket and see if there's any trace damage. You might also want to reflow the solder on the socket legs.

PCM samples are handled by the Nanao GA20 chip on the top board. You might want to reflow the solder on it too.

@caius has worked on a few M92 boards - he might have some other ideas.

 

[NFGx]

I fixed it!

Hairline crack on the trace leading to the Yamaha D2 line. Bridged that, and it came back to 100%.

 

[ShootTheCore]

Great find! Glad you fixed it.