MV1FT/MV1FS no stereo

Hi, I have two 1slots that I can't get to put out stereo sound. They're pretty similar, one MV1FS and one MV1FT.

Any ideas on what to try would be much appreciated - I've used the search function here and have googled quite a bit without luck... maybe I'm too stupid to use the search though. I figure this might be a quite common problem, not only because of the warning stickers on the cart guides and in the manuals ["Note) It my cause trouble on P.C.B. by miss-setting" ] but also because I've seen quite a few people using their boards with JAMMA harnesses and the switch set to stereo.


I’ve connected my hifi with cables I soldered myself to the 4PIN interfaces. Here’s the pinout used btw. I've also tried switching which pins the cables go to, but that didn't do any good. The MV1FT doesn't output anything through the 4PINs, the output on the MV1FS is very low and not stereo (the setting of the stereo/mono switch doesn't change the audio one bit). There don't seem to be any broken traces or bad soldering points on the boards.



Maybe I should shotgun the caps in the audio section of each board? I've been wanting to do that for some time anyway to improve on the sound quality. Couldn't figure out which of the caps could stay though, so I haven't done it yet. I hope it's alright that I'm asking about it in this thread as well... here's two pics of the audio sections (click to enlarge):


MV1FS


MV1FT

These boards are not in channelmaniacs pdf guide (yet?) and even though I have some soldering skills, I’m not too self-confident about deciding which ones to replace, since the guide lists different numbers for different 1slot boards and he’s also selling different kits for MV1, MV1FZS and MV1F. I read that the "electrolytic ones except the filtering caps" need to be swapped, but how do I tell which ones those are?

Have you tried getting stereo out the headphone 4-pin connector? On my MV-1F running with the switch set to stereo I get good stereo from the headphone connector but "semi-stereo" (where the left channel can be heard at about 50% volume on the right speaker and vice-versa) from the speaker connector. This was after a complete recap.

Thanks for the tip. I've been fiddling about a bit and you were right, there is "semi-stereo" - I needed headphones to be sure though.


1FS:
Speaker 4-pin connector: switch to stereo = semi-stereo, 50%/100%.
Headphone 4-pin: switch to mono or stereo = semi-stereo, 20%/100%.
--> What could be done to improve upon this? Cap Kit?


1FT:
Speaker 4-pin connector: switch to stereo = semi-stereo, 50%/100%.
Headphone 4-pin: didn't work at all at first. Tried applying contact cleaner to the top of the volume control, put some under it with a cotton bud. Got the left channel to work after pushing the slide around, had a lot of crackling sounds but only on the left channel. There seems to be semi-stereo as well (switch to stereo or mono), because the left channel get's reduced in volume by about 50% when the right channel is chosen in the audio test screen.
--> How to clean the volume control effectively? I believe the contacts are on the bottom side which is hardly accessible with it installed... guess I'll have to desolder it?
--> Has anyone seen the part for sale anywhere? (So if I'm desoldering it anyway, I could put a new one in there).
--> Could the volume control be bypassed?
--> What can be done to improve upon the semi-stereo? Cap Kit?

xsq said:

Thanks for the tip. I've been fiddling about a bit and you were right, there is "semi-stereo" - I needed headphones to be sure though.


1FS:
Speaker 4-pin connector: switch to stereo = semi-stereo, 50%/100%.
Headphone 4-pin: switch to mono or stereo = semi-stereo, 20%/100%.
--> What could be done to improve upon this? Cap Kit?

Click to expand...

I don't think a Cap Kit will help - on my MV-1F I replaced every single capacitor on the entire audio circuit with a new one and it did not help with the semi-stereo.

xsq said:

1FT:
Speaker 4-pin connector: switch to stereo = semi-stereo, 50%/100%.
Headphone 4-pin: didn't work at all at first. Tried applying contact cleaner to the top of the volume control, put some under it with a cotton bud. Got the left channel to work after pushing the slide around, had a lot of crackling sounds but only on the left channel. There seems to be semi-stereo as well (switch to stereo or mono), because the left channel get's reduced in volume by about 50% when the right channel is chosen in the audio test screen.
--> How to clean the volume control effectively? I believe the contacts are on the bottom side which is hardly accessible with it installed... guess I'll have to desolder it?

Click to expand...

I would first try giving it a good blast with a can of compressed air - use the little plastic tube attachment to direct the air right where you want it.

xsq said:

--> Has anyone seen the part for sale anywhere? (So if I'm desoldering it anyway, I could put a new one in there).

Click to expand...

I have never looked for an exact replacement but it is just a dual 1000 ohm potentiometer. You could certainly get an equivalent part though it might not look exactly the same as the original. If you really want a replacement for the original part you may need to get one from a donor parts board.

xsq said:

--> Could the volume control be bypassed?

Click to expand...

Yes you can replace it with some resistors, and I have done that for diagnostic reasons on occasion, but then you lose the ability to adjust the volume.

xsq said:

--> What can be done to improve upon the semi-stereo? Cap Kit?

Click to expand...

I have wondered about this myself and I don't really have an answer yet. Sometime when I have the chance I will compare the "semi-stereo" on different boards and different models and see if there are any differences in the audio circuit.

I have the same board and I was having some audio problems too.
But after cleaning the switch, stereo works just fine, in hardware tests left and right channel sound like they're suposed to (before cleaning right wouldn't always work).

And like the manual says don't connect a speaker to the Jamma connector if you're using the stereo speaker out.