What's new
By:
Filters

MV1FZ Audio cap kit...noisy in the background

A

andynumbers

Professional
Joined
Jan 3, 2017
Messages
257
Reaction score
266
Location
Atlanta, GA
So here's a weird phenomenon I can't find anything about. I replaced all of the capacitors on a working MV1FZ. Afterwards, the audio works, but there's a lot of humming/noise on a quiet screen. What's really strange is that the noise gets extremely loud when I place my finger on top of the four 4.7uf capacitors that are in a line in the audio amp section. Almost like it's acting like an antenna picking up noise out of the air.

Has anyone else experienced this problem before?
 
Which caps did you use? Not all are ideally suited to audio.
 
Ground issue. Your ground path might not be big enough.
 
Did not replace the amp and pot. They were working fine before the cap replacement.

Caps used were a mix of Panasonic 105 FC/FR and a few SILMIC II that I had lying around.

@xianxi: How can I correct this? Ground all of the negative leads manually on the caps? One gripe about this board is that the ground planes are large and you have to heat the hell out of them to flow solder.
 
Not sure if this is may be the cause, but Panasonic FR have way too low ESR so I wouldn't use them as replacement for general purpose caps. I ran into problems twice recapping Sega Mega Drive consoles with these capacitors and the problem dissapeared when I replaced them with general purpose caps.

My problem was video noise after ~1h running, probably due to oscillations in the 7805.
 
It's strange to think that good caps may be "too good" in this case. I may try to replace with all SILMIC or MUSE audio grade caps and see if that fixes it.
 
andynumbers said:
It's strange to think that good caps may be "too good" in this case. I may try to replace with all SILMIC or MUSE audio grade caps and see if that fixes it.
Click to expand...
Maybe some faulty cap or ground issue like XianXi said, i replaced all the cap on a mv2f with panasonic low esr caps (idk if they are the same you used) and no issue at all on my side.
 
Have you given the board a good clean? As in the PCB, perhaps there's some flux or speckle of solder that needs to be cleaned up.

Also, do the Zs have a volume slider or pot? If so, give that a clean too.
 
Good idea -- the flux residue could be causing a minor short circuit. I'll give it a good cleaning and see if that helps.
 
Cleaning off the flux did not help. Next step I will order some audio grade caps and see if that fixes the problem.
 
I would say you probably severed a trace or damaged a via while desoldering the old caps and now you have a floating signal somewhere.
 
Thought I'd bump this up. After taking a closer look the problem is with two specific caps that are attached to the DAC's pins 10 and 11 which are the audio L and R channels. When I place my finger or hand or whatever near these caps the noise occurs. Almost like my body is acting like an antenna.

Here's a video that shows the problem. (Turn volume up or listen with headphones):

In the video you'll see it only happens with these two specific caps. The caps have now been replaced with ELNA SILMIC II 4.7uf 25v, which is the highest grade audio caps you can buy.

How can this be fixed? If you look at the schematics for the original MV1F here: https://wiki.neogeodev.org/images/9/9c/Mv1fs-page4.jpg you'll notice you won't see these capacitors (YM3016 pins 10 and 11 CH1 and CH2). The 272M resistors to GND exist on the schematic and on the MV1FZ, but not the caps. I wonder can these caps be bypassed, replaced with capacitors or a different type or value to fix this problem? Could the YM3016 itself be bad?

Edit: One last update: I plucked two old 4.7uf caps off another Neo Geo PCB and put them back on the 1FZ and still no change. At this point I'm pretty convinced it's not a cap issue but something else. Should I bother attempting to replace the YM3016?
 
Last edited:
Replaced the pot...no effect. At this point I think this is going to be shelved as a parts board. I will just switch to a 1B or 1C.
 
You must log in or register to reply here.
Back
Top