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Oh, there's a couple of RAM chips that IIRC are connected to that chip too. If they've gone bad that could also potentially explain the issue. Get the logic probe in any case, it's a must have tool for troubleshooting. Good luck!

There's a big chip in the corner of the bottom board. Try pressing it down with the game running. If there are changes to how the sprites look it may be the case that it has cold solder joints. That would explain the issue and could be addressed by reflowing it. If that doesn't work, it may have...

Try detaching the two boards and reattaching them again. The connectors may be making poor contact. Doing it a few times may help restore the connection.

Seems like a great alternative to a repro of the Batman Returns sound board -- and much cheaper than using the original DSP. If I recall correctly the STV handles sound effects and the add on board the music; mixing them can be done easily enough, and the same board could be used for STV and...

Still alive, real life got in the way. I'll give an update next week, I have a few days off.

There are two types of 1 megabit ROMs with slightly different pinouts. Those are mask ROMs so I'd expect them to use... Mask ROM pinout. Search for 27c301 pinout, it's the same as the one used on mask ROMs. If your programmer doesn't support this type you can make a simple adapter to the more...

Hello!

Bad checksum may mean that the flash chip on the motherboard is bad. You could try to replace it.

What @ack said :)

What version of the MV4 is it? The big one with loads of ICs or the newer with SMD customs?

I don't think you've created a mess for yourself, just changing the volume wouldn't have caused the board to stop booting. With that said, it's a rather strange situation. Start by checking the voltages at the board edge and, if your board's BIOS is socketed remove it and insert it again. If...

It's not bad if the sprites came back. There's probably a bad via or pad connection underneath the chip itself. Proceed as @stj described and check if the vias connected to the pads have continuity before resoldering the chip.

Maybe my wording wasn't the clearest. I was suggesting getting the normal running temperature range of good ones to compare with suspected bad ones. It would help with basic troubleshooting I think.

Oh, another thing. If either chip is *hot* it's shorted and therefore dead. Maybe we should start taking temperature measurements of normal functioning chips for reference. What do you think @Hammy ?

Very bad solder joints on these things... Place the board on a flat non-conductive surface. Turn it on. Apply pressure to the 55555 and the other chip like it and see if glitches appear. Alternatively, gently (gently!) touch the pins of the chips. With dry hands of course. If glitches appear...

The Z80 you used is fine. My RFJ is stored away otherwise I'd check it for you. The fact it always hangs in the exact same spot suggests that whatever is causing the freeze is probably related to a memory access. If you have the means to dump the program ROMs (main and audio CPU) I'd try that...

Make sure the Z80 is fast enough. I think it's a 6 or 8 MHz part. The reset button should (gasp!) reset the board. Now that I think of it, I had to resolder it too, it had the same behaviour as yours. Start with the oscillator and reset switch and see if the problem goes away. Grab a logic...

Yes, just the 4 pins underneath. My board had very little solder on those pins. Try applying pressure or slightly flexing the board to see if it behaves differently -- freezing sooner or later, glitching, etc. This would indicate cold solder joints on one or more SMD chips -- usually this...

F*ck me. PM incoming...

Great work, congrats!