Donkey Kong Trouble - Can't get sound working in original DK cab

[nate1749]

I'm not sure if this is the right spot for this thread, but I couldn't find a more specific one and didn't know where else I could ask for help so...

I have an original Donkey Kong cabinet that I bought about 6 months ago and up until a month or two ago everything worked fine.  Then the sound/music started to fuzz/static out, I went to the back of it and turned the volume up and it seemed to 'kick' back in, but then the problem started again.  I turned the volume all the way up and then the sound would go from nothing to 100% - since 100% loud is way too loud (especially since it's in my work) I turned it back down, but then the sound would go out again.  It almost sounded like a weak connection of speaker wires if you've ever had that problem and when you crank up the volume then it kicks in. 

Anyways, then turning the volume up to max wouldn't even kick the sound back in (where I am now), instead it's just a weird (and very light in sound) twilight zone type of sound "woo-woo-wooo-wooo."  So I'm guessing that noise is some type of electrical noise since when the machine is powered off no noise is of course made.

So me not knowing anything about arcade cabinets decided to start replacing parts.  I replaced the sound amplifer, the sound cable, and the speaker itself and I still have the same problem.  I'm not stuck and have no idea what it could be.  I'm afraid it might be some part on the mainboard that would need to be soldered off/on, but like I said, I'm clueless. 

Does anyone have any more troubleshooting options/tips or how I can check anything else.  I will say that inside the DK there is a part that i have no idea what it does but that the sound plugs in on one end and comes out again on the other end so I'm thinking that might be the culprit (but again so far my shots in the dark have all missed).

Nate

[SirPeale]

The sound amp likely needs to be capped.

[nate1749]

I bought the replacement sound amp from quarter arcade and according to their description .." This board has been completely rebuilt, all caps have been replaced and it is fully working. "

http://www.quarterarcade.com/GamePicture.aspx?c=&g=7119&o=5&m=0&i=1&t=6

Do you still think the sound amp needs to be capped?  I'll do some more searching later on what that is and how to do it - thanks for a direction to go in =)

Nate

[RayB]

dirty potentiometer?

[Level42]

Yes, that was my first thought as well. You replaced (about) all the parts except the one you actualy noticed the problem with: the potmeter. Get a new one, forget about sprays etc. those fix it only temporary and then make things worse.

The sound you're hearing when it's turned fully up is noise coming from the electronics inside the cab, most likely the PCB. Most harnesses don't have the audio wires twisted, so they are very easily picking up noise.

That's normal and kind of acceptable in  cabs that used to be in loud surroundings, and you won't notice it (much) on normal sound levels.
 

[SirPeale]

Missed the part about replacing the amp, sorry.

[nate1749]

Thanks I'll look into getting a new one of those.  Any recommendations on where?  I e-mailed QA so hopefully they'll have something, couldn't find anything on google.  Thanks again.

Nate

[Level42]

Radio Shack ? Bob Roberts ?

[nate1749]

Still having trouble finding this part, everyone i talk to says they don't deal with parts that small.. just to clarify, im just trying to replace the knob on the small board - would it be possible for me to just buy a new board for somewhere (that tiny one).  At this point I just want it to work so I'm not trying to save a few bucks on finding some part noone seems to carry.

Nate

[CheffoJeffo]

The Real Bob Roberts ?

http://homearcade.org/BBBB/parts.html

EDIT: I posted a picture of the wrong pots.

[ncflagg]

I had a similar problem while converting my super mario back into DK. I had the sound working and then it wasn't. I messed with the volume on the monitor and it worked again for a bit. I finally traced the problem back to miswiring on my part. I had the "unamplified audio" and "speaker +" hooked to the sound input on the monitor. "speaker +" should have been "ground".

DK Pinout
http://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=pinout&page=Nintendo_Classic.html

If your machine is also hooked up via the edge connector you might try bypassing the sound hookups directly to the "tv audio" (i think) connector. It's 4-pin but only the left two (ground and sound) are needed.

[nate1749]

Thanks for the link to the Bob Roberts site, but he also doesn't have that part.  He e-mailed me back and said he only has video pots (he also said he doubted the audio pot was the problem unless it's physically broken on the monitor - I thought the audio pot wasn't even on the monitor and was on that small board I mentioned earlier so I don't understand his response)...   I will look at the wiring, but I know before it couldn't have been wired wrong since it worked fine and then problems began to happen and then as one of the fixes I replaced the speaker.  If anyone knows anyone in Chicago that fixes these things or sells arcade parts around here please let me know.  The only store I have left to try is Fry's and that in the suburbs, but it's worth a shot.  Thanks.

Nate

[Level42]

Any (on-line) store in electronics should carry audio potmeters.

How about http://www.mouser.com/Search/Refine.aspx?FS=TRUE&Ne=688737&N=254357+4294966040+1323038&Ns=P_SField ?

[Ken Layton]

Here's some refresher info on Nintendo Sanyo monitors:

Audio amplifier board as well as the volume control board are mounted on the monitor frame.

Audio amplifier board gets it's power from the monitor main board. So if the monitor has not been recapped then the audio board may be getting 'dirty' or 'noisy' power from the monitor main board.

The volume control trimpot is mounted on the small 'adjustments' board next to the audio amplifier board on the monitor frame. Sometimes it may develop bad solder joints and simply needs resoldering. Sometimes the pot can be sprayed out with specialized volume control cleaning/lubricating spray chemicals. Sometimes the thin layer of carbon inside the trimpot wears through and this is when the trimpot must be replaced.

Bob Roberts has all sorts of trimpots for sale as they come in many sizes/styles/resistance values. Trimpots are used in many applications including audio, video, and power supply adjustments.

[nate1749]

I never replaced any parts, but I get annoyed w/it so I just turned it off for about a month and when I turned it back on the sound has been working fine since (about 6 months now).... very strange...