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Author Topic: Sound buzz (noise) on D.E  (Read 4310 times)

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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #30 on: December 14, 2008, 01:49:23 PM »
OK, its off without wood or damage!

I put a peice of 1.25" think foam under the transformer just for a test.  A little better.  However the only thing which makes it go away is to disconnect both display speakers!

From before, there was a humm with all speakers removed.  With the foam thats better.

So, I'm guessing there is noise coming into the sound on power somewhere?  I don't care about the G.I noise, just this damm humm.   !!!
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Marty Machine

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Re: Sound buzz (noise) on D.E
« Reply #31 on: December 14, 2008, 01:53:31 PM »
Understood, you're fighting 2 battles.

Is the cabinet hum (no speakers attached) really bad?

Maybe the main step is to focus on the speaker hum and fixing faulty supplies etc.

MM.
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #32 on: December 14, 2008, 01:56:35 PM »
No.  With foam under the transformer (btw, if I cut it the same size, is it safe to leave under it?) with speakers (only backboard) detached is fine now.

Cab speaker left in, no different.

Once I reattach backboard speakers, loud humm is back.
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Marty Machine

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Re: Sound buzz (noise) on D.E
« Reply #33 on: December 14, 2008, 03:48:05 PM »
Depends how hot tranny gets, and if foam is easily melted.
A small sheet of ply/chipboard between the foam and tranny would certainly help.

can u extend backboard speakers and move away from cabinet to see if it improves? (might be too close to tranny?) otherwise it's still sounding like hum in the amplifier audio path.

MM.
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #34 on: December 14, 2008, 03:48:48 PM »
What I've done this arvo on this:

  • rather than mount transformer on foam, I've used 4 x post rubbers (blk) under each foot and screwed back in
  • removed sound board, ppb board & power board, sanded and cleaned each pad (for gnd) and re-flowed each and every connector pin

No different....

I havn't bothered with the CPU board as yet as I don't know if it will make any difference.?
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Marty Machine

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Re: Sound buzz (noise) on D.E
« Reply #35 on: December 14, 2008, 04:05:45 PM »
At least you've prevented a whoile lot of other problems down the track by cleaning re-soldering on the boards.

Do you have a manual for LAH? if i can check out the schematics i can tell you what to look at.

MM.
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #36 on: December 14, 2008, 04:34:29 PM »
Quote from: Marty Machine on December 14, 2008, 04:05:45 PM
At least you've prevented a whoile lot of other problems down the track by cleaning re-soldering on the boards.

Do you have a manual for LAH? if i can check out the schematics i can tell you what to look at.

MM.

The closest I had was these:

http://iobium.com/Pinbxxxx/Data%20East/Service/Data%20East%20Schematics.pdf
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #37 on: December 14, 2008, 05:48:00 PM »
 !@# !@# !@# @@^

OK.  ALL boards have been removed, pads cleaned and ALL connector pins reflowed completely.

I am beginning to think perhaps the PSU is causing these issues....I've checked the PSU with the following voltages recorded:

  • - 12vDC is reading -14.68vDC
  • +12vDC is reading 11.51vDC
  • +5vDC is reading 4.97vDC
  • (On CPU board)
  • +5vDC is reading 4.9vDC

I have no idea whether the unbalanced DC can cause these issues.  Game is functioning 100% however will need to be cleaned up...
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Marty Machine

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Re: Sound buzz (noise) on D.E
« Reply #38 on: December 14, 2008, 06:14:27 PM »
Those readings seem to be in spec enough, although the -12 (being -14) might have AC riding on it.

Can you measure AC volts with your meter? measure ALL those supplies again on the AC setting, and see what you get.
I would hope all supplies only show something like .2v (200mV) or preferably less.

MM.
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #39 on: December 14, 2008, 07:46:34 PM »
I tested as suggested on the CPU board.  With the DMM set to X.XX on AC I got readings of 0.02vAC on the -12v and 0.25vAC on the +12.  On the board (at the test points) it states unregulated so I don't know if this is a good indication.  On the +5v on the CPU board I got readings of 0.00vAC.

There has to be something worn / not working somewhere as Mark's LAH at the factory is 80% quieter than mine...

Hmmm...
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Marty Machine

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Re: Sound buzz (noise) on D.E
« Reply #40 on: December 14, 2008, 08:29:36 PM »
All looks good, nothing to be alarmed about.

Can you measure volts on your sound board, both DC and AC.

MM.
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #41 on: December 14, 2008, 08:45:52 PM »
Quote from: Marty Machine on December 14, 2008, 08:29:36 PM
All looks good, nothing to be alarmed about.

Can you measure volts on your sound board, both DC and AC.

MM.

I will have to do tomorrow night.  Been doing stuff all day and had enough for tonight..Don't want to break stuff as this usually happens when I'm tired.

FYI...Everywhere I google on RGP etc about this issue, the number one thing is grounding.  Now, all board screws are in tight...Just for shits n giggles, I put the DMM on buzz and tested all grounds I could reach, within backbox & to earth pin on power plug.  No problems located and it appears that ground is getting from backbox to earth pin on power.
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #42 on: December 15, 2008, 07:19:59 PM »
Hiya,

OK voltages are the same as above tested on TP's on PSU.  AC checked out the same as well on the +/-12 & +5v.

After looking at schematics all day, I also replaced all 470uf 25v caps on sound board.

Fired her up, same.

The problem is the more I try to fix it, the more annoying this noise is getting.  I am now completely out of ideas. So unless its dirty power coming from the PSU I'm stumped.
« Last Edit: December 15, 2008, 07:51:42 PM by MartyJ »
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Offline MartyJ

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Re: Sound buzz (noise) on D.E
« Reply #43 on: December 15, 2008, 09:54:31 PM »
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Marty Machine

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Re: Sound buzz (noise) on D.E
« Reply #44 on: December 16, 2008, 12:48:30 AM »
Yep, i read a similar article recently about turning down the gain of the audio amp.

As much as this 'bandaids' the problem, it's not really a fix.

There's still a reason WHY the amplifier (at original high-gain) is so succeptable to picking up the hum and passing it thru.

Call me old fashioned, but i like to ELIMINATE problems, not cover them.  &&

MM.
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