MVS MV-1A, missing sound - (attempted) repair log

[invzim]

So I take my MV1A out of storage, and for some reason sound is completely missing. I fire up the hardware test, and same as game - completely silent.

First thing I check is the amplifier section, I buzz the output of the DAC on pin 10 & 11, which is amplified no problem, and volume pot is working - so the amplifier section seems ok. http://wiki.pcbotaku.com/w/index.php/YM3016.

Further on to a beast of a chip, the YM2610 - http://wiki.pcbotaku.com/w/index.php/YM2610. Finally the purchase of an oscilloscope will pay off, at least that's the idea .

The part has 64 pins so I'll spare you the details, but one thing I finally find a bit odd is that RD, WR and Chip Select (pin 57,58 and 59) are stuck high. These have activity on my working MV4, so surely this must be the problem. They trace back to pin 47,48 and 49 on the SNK NEO-D0 custom chip.

After a bit of hot-airing, solderwicking, isopropanoling and resoldering, the NEO-D0 from my working known-good MV-4FS is now on the MV1a with not much difference. The MV1A is still silent, and RD, WR and CS are still high.

One thing is different though, I installed the NEO-D0 from the MV-1A in the MV-4FS, and now that is silent too .

[channelmaniac]

OK... don't go too hog wild here...

MVS audio issues are as follows:

Bad caps in the audio section - VERY common
Bad Z80 CPU - VERY common and should be replaced with a faster Z80A CPU
Bad Sound ROM - Not so common - BE CAREFUL when replacing
Other bad chips - Pretty rare.

The Sound ROMs used on Neo Geo game boards can be different! There are 2 main types of 1Mb ROMs - JEDEC compliant and non-JEDEC compliant. They are NOT interchangeable as A16 and one of the enable lines are swapped between the 2. Use the # listed on the silk screen or the part #s on the ROMs to determine which type it is before you condemn it as bad when swapping between 2 different boards. If they are the same type then yeah, it's probably bad. If it's different then you might just be running into a pinout issue.

RJ

[invzim]

Thanks for reply!

The Z80, actally a SMD thingy called 84C00AM-6 looks healty to my untrained eye:
/halt high
/iorq high
/nmi high
/int high
/busack high
/wait high
/busqr high
/reset high

/mreq active
/rd active
/wr active
/rfsh active
/m1 active

CLK active (4MHz)
A0-A15 Active
D0-7 Active

Not sure how I should go about replacing, or even testing the sound PROM, as it's a TC531001 SOIC package - http://wiki.pcbotaku.com/w/index.php/TC531001" , and also looks healthy on the scope.

When the MV4FS was working, the YM2610 clearly had visible digital output to the DAC when doing the sound test, but on mute MV1a this is just a constant 111khz signal (just like silence). You think caps can infulence the YM2610?

I may try to swap the NEO-D0's again to see if I can get sound back to the MV4FS.

[channelmaniac]

No. Caps won't affect the digital part of the audio system on the MVS

[channelmaniac]

If anyone needs one of those pesky surface mount Z80 CPUs, the only place I've been able to find them is inside a Sega Game Gear.

RJ

[purplec]

When will your site be back up?

[channelmaniac]

Whose site?

[KmanSweden]

Non of your links work.

[davewellington]

(pcbotaku)

[invzim]

I hope to have pcbotaku up this week or next.