Nintendo Hum - SOLVED! (20EZ buzz)

sand1

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Hi all!

I believe I narrowed down what causes the "Nintendo hum" and how to fix it.

I recently picked up a Donkey Kong and a Punch-out. The hum produced by DK was annoying and the PO hum was obnoxious.

After reading though dozens of Nintendo hum related threads I found lots of possible solutions mostly relating to rebuilding the 20ez audio amp or recapping the game's power supply. Most people reported these solutions did not work for them. Others reported using a separate 12v sound amp and some said they designed their own amps for Nintendo games. While others simply stated "that's what Nintendo game do".

I tried the following ...

* Recapped the power supply (didn't help)
* Rebuilt the 20ez audio amp (didn't help)
* Rebuilt the 20ez rectifier circuit (didn't help)
* Put a 430uf cap across the speaker output (this filtered out most of the hum but also made the game sound like you were playing it underwater)

Then I found the last post of this thread...
https://forums.arcade-museum.com/showthread.php?p=3014160#post3014160

The post above suggested unplugging connector JB, moving C379 to the "correct" position and installing a 50k pot at VR371. This made sense as the wire going from connector JB to the adjustment pot board utilized the only shielded cable in the entire cabinet. Eliminating this cable entirely might help. So I ordered a few of these pots http://www.digikey.com/short/3912b7

To be clear, you must permanently disconnect JB. This will disable the original sound pot. All sound volume adjustments will then be made directly on the amp board.

See a before and after below...

attachment.php


I tried this on three different audio amps (two rebuilt and one original) and it solved the hum in all three cases.

-Sean
 

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Am I correct, in assuming this could be used for a coindoor mounted solution? Solder wires on the amp pcb and run a mini harness to this pot?

http://www.ebay.com/itm/B50K-50K-Oh...014173?hash=item3d1bb779dd:g:ZOMAAOSw6btXScWs

The hum is likely caused by the wires going to the remote adjustment board. (which the solution above eliminates) Adding your own wires will probably cause the hum to return.

If you want a pot in the coin door you should wire the pot to the speaker wires making a standard "L-pad". (See below) Most games that have a pot at the coin door use a L-pad setup. A 100 ohm 5 watt pot should work, but I haven't tried this (yet).

attachment.php


If you add a pot on the speaker wires at the coin door then the pot on the audio amp becomes your "max volume".

-Sean
 

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Thanks. One other dumb question. Is the original volume pot also 50k? Meaning could I relocate it to the amp pcb since it wouldn't be needed after the mod anyway? Then, the small harness for JB could be desoldered and discarded (or saved for originality).

EDIT: I googled and the original is 50K. :D
 
Hi all!

I believe I narrowed down what causes the "Nintendo hum" and how to fix it.

I recently picked up a Donkey Kong and a Punch-out. The hum produced by DK was annoying and the PO hum was obnoxious.

Nice fix never bothered me when I owned them then again when you have 40-50 games on and Jukebox going you don't hear it.Time for a Jukebox my friend
 
Thanks. One other dumb question. Is the original volume pot also 50k? Meaning could I relocate it to the amp pcb since it wouldn't be needed after the mod anyway? Then, the small harness for JB could be desoldered and discarded (or saved for originality).

EDIT: I googled and the original is 50K. :D

You certainly could relocate the original pot and remove the wire harness if you want to. The original pot seemed a bit too small and hard to get at when attached to the amp.

-Sean
 
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Hi all!

I believe I narrowed down what causes the "Nintendo hum" and how to fix it.

I recently picked up a Donkey Kong and a Punch-out. The hum produced by DK was annoying and the PO hum was obnoxious.

Nice fix never bothered me when I owned them then again when you have 40-50 games on and Jukebox going you don't hear it.Time for a Jukebox my friend

You are right, it was harder to hear if there were other noises. It was most annoying late night when the only thing on in the whole house were the games.

-Sean
 
Nice! I am glad to hear this is working for others.

-Sean

I didn't have a spare pot on hand, so I moved my original and still have hum and now a little faint beeping as well. I do have Remix currently installed, so not sure if that could be a factor.
 
I also have the Remix kit installed but did use a 50k pot from another parts Sanyo chassis for the audio board.

I haven't tweaked my volume pot on the PCB itself. I'll mess around there later and see if I can balance it out.
 
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