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MV2F losing sound if 2nd slot is accessed

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Ryoandr

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I have this MV2F slot that I repaired, and if I use the 2nd slot, I lose sound forever, like doing :
-1 game on slot2
-2 games, when I select slot2 game, sound is gone, and doesn't come back after selecting back slot1 game.
I know unibios4 has a no-sound bug with no game on slot1, but this also happens on a stock bios.

I tried swapping NEO-257s, NEO-E0s, NEO-G0s around, even swapping 257s from the graphic side, tried changing YM2610 as some signals seem to lit dim on my logic probe, and then disappear a few seconds after slot switch. The diagbios show Z80 errored/dead if trying to test on slot2 with up so I also tried another Z80 but no progress. Tried clear memory (all DIPs down), same...Even tried changing some mildly related chips like D0, I0, F0.
 
Yeah, diag jingle beeps in slot1, nothing in slot2.
I think I checked SDA/SDD, but I'll recheck again later, can't never be sure.
 
Some more info, this is mostly from a post I made a week ago on another forum where someone add a similar issue.

When the board initially boots, the z80 will be running the code from the sm1 rom that is on mv2f board. When the diag bios goes to enable the diag m1 in a specific slot, it will first send a command to the z80 (still running the sm1 code) telling it to prepare for the switch, at which point the z80/sm1 will reply back saying its ready, and then the diag bios does the swap and diag m1 is enabled (and also the s rom on the cart). Since you don't get the "Z80 SLOT SWITCH IGNORED (SM1), SM1 OTHERWISE LOOKS UNRESPONSIVE" warning, its implies the 2 way communication between the 68k and z80 is working as the prepare for slot switch request/response worked ok

You've already proven that the sound subsystem is working since you get sound on slot 1. This means the z80/ram/ym2610 and audio amp are working ok. This is also another indication the 2 way communication is working or games wouldn't be able tell the z80 to play sounds.

After the slot switch, the diag m1 code should start running on the z80. The diag m1 is not dependent on the diag bios to run. The first thing the diag m1 does is play an initial jingle to indicate its alive (it plays in additional jingle when it finishes testing, if there are no errors). The fact that you aren't hearing this in slot 2 implies the diag m1 code is not running. Which points to some issue with the address/data/enable lines between the z80 and m1 rom in slot 2. Since this is only happening with slot 2 you should look for issues between the slot and the mulitplexer IC (NEO-257?) for the data lines and whatever buffer ic for the address lines go to.

One of the tests that both diag roms do is to try talking to each other. The "Z80 Dead / errored / comm issue" is the bios saying it tried to talk to the diag m1 and got nothing/garbage, which would be expected in this case since it appears the diag m1 isn't running.
 
check the obvious first - look closely at the edge connectors for bent contacts, cracked soldering or crap stuck in the slot
 
Should have mentionned it but I checked for cart pins and soldering.
checked how signals are wired :
SDA0-15, SDMRD, SDROM, SDRD0, SDRD1 are shared between both slots, all cart pins are correctly connected to both slots and K10 NEO-E0 that should buffer correctly since slot1 fully works.
SDD0-7 are separate to each slot, and go to H9-NEO257, no trace broken between them.
As I said I already tried changing the E0 and the 257.

Also rechecked the error message on Diagbios and it's
(no beep)
Z80->68k comm issue (Hello)
Expected : C3
Actual: 01
 
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