SNK Neo Geo MVS Fixing Multicart PCM Sound (& Stability) – 120 in 1, 138 in 1, 161 in 1 (& Others)

A long video covering the mods required to get PCM sound working properly on many of these cheap MVS multicarts. I’ve covered some old ground here from the previous video on the 138 in 1 cart, in order that it’s all in one place. The latest additional bypass caps fix the PCM issues I have been experiencing since I first noticed a problem with NAM-1975 back in November 2013.

I have applied the fixes to 120 in 1, 138 in 1, and 161 in 1. This has completely fixed any sound issues I was experiencing on many games – some I didn’t even know were a problem due to how minor the glitches were. Some of the games affected the most were:- Pulstar (on 161 in 1, and 120 in 1), Metal Slug, Blazing Star, Rage Dragons, Strikers 1945+, Neo Turf Masters, KoF (several), and many many others where glitches were very minor.

It is very likely the same fixes need to be applied to many (if not all) of the other MVS Multicarts.

Tested on 5 different multicarts and all 5 are perfect now. I am amazed at how good these carts sound after doing the mods. On the 120 in 1, C3 and C4 on the PRG (top) board need the 47pF bypass caps – those fix SDRMPX and SDPMPX (PCM issues). On the ‘new’ 161 in 1 board, C5 and C6 are positions for the 2 x 47pF caps, so you don’t need to scratch traces to add the PCM fix caps on that newer 161 in 1.

138 in 1 and 120 in 1 pics:-
https://www.dropbox.com/s/nx0fhk0eimacrpi/multicartfix.zip?dl=0

161 in 1 pics:-
https://www.dropbox.com/s/kdf1bd2fqow6xkv/161%20in%201.jpg?dl=0

120 in 1 Voltage Regulator & Caps
https://www.dropbox.com/s/gg6b2gl70d89nmo/120%20in%201.zip?dl=0
Confirmed it works on the 150 in 1 as well. (Uses the same board as the 161 in 1).

09/11/2015 – One thing to note, I am not 100% sure whether 47pF is the ideal size for those 2 capacitors. On my 138 in 1 I get no sound issues at all with 47pF capacitors, but I recently played all the way through Pulstar on the 161 in 1 and a couple of times the sound did glitch, but hardly at all and very infrequently. This makes me wonder if 47pF might need changing to 57pF or 37pF etc. When I get more time I will retest with a slightly different size and report back.
21/12/2015 – Very hard to get it to glitch at all when using 47pF caps. I played on the 161 in 1 all weekend and never had a single issue. I think the ambient temperature and humidity is a factor also.