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Tom Schulten

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Since: Jan 08, 2006
Posts: 3



(Msg. 1) Posted: Sat Jul 15, 2006 9:15 am
Post subject: Qbert sound problem (newbie)
Archived from groups: rec>games>video>arcade>collecting (more info?)
I have a Qbert CT that has a single constant tone coming from the speakers.
The Qbert sound flow chart or the Gottlieb system 80 repair guide doesn't
show a fix for this. I have replace lm3795 amplifier and repair the power
supply board. The lm3795 fried shortly after I first power it up because of
48dcv being sent to the lm3795. And it was doing same thing before the
lm3795 fried. All my voltages are good +30v actual +28.52v, +5v actual
+5.003, +12v actual +12.13v, -12v actual -11.92v. The test button or the
dip switches changes doesn't affect the sound board. I have unplug main pcb
and power just the sound board, the same sound is being produced. I have
pulled the voice synthesizer chip then power up and have no sound. But I
should being getting something from u20 1408? Could it be a bad r6532 roit
(u15) sending bad signal? How can I check this? I have a oscilloscope if
this helps but very little background in electronics.

Thanks for the help,
Tom

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Bret Pehrson

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Since: Jul 26, 2005
Posts: 158



(Msg. 2) Posted: Sat Jul 15, 2006 9:15 am
Post subject: Re: Qbert sound problem (newbie) [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Tom Schulten wrote:
> I have a Qbert CT that has a single constant tone coming from the speakers.
> The Qbert sound flow chart or the Gottlieb system 80 repair guide doesn't
> show a fix for this. I have replace lm3795 amplifier...

That is a lm379S, not 5, right? (It should be an S.)

Have you checked the filter board? Those often fry in these cases.

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JB

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Since: Mar 26, 2005
Posts: 4



(Msg. 3) Posted: Sun Jul 16, 2006 11:39 am
Post subject: Re: Qbert sound problem (newbie) [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
Tom Schulten wrote:
> I have a Qbert CT that has a single constant tone coming from the speakers.
> The Qbert sound flow chart or the Gottlieb system 80 repair guide doesn't
> ...
> Thanks for the help,
> Tom

The best way to tackle this is to really get your hands dirty and build
a sys80 sound test rig. Marvin's has a diagram/walk through on his site
somewhere so you might want to google for it
(www.marvin3m.com/fix.htm). Most likely you have an issue on that sound
board (although there is an output chip on the main Q*bert board that
*can* can bad particularly if you've had issue with the knocker. From
memory... so check the schemas).

At any rate, a very frequent issue with Q*bert sound is stuck inputs.
This locks up the sound board and you won't get any sounds. Read up on
marvin3m. Remember the sound board is identical to the ones used in all
those sys80 pins....

If you're hearing tones, you're amps are fine. You need to focus on the
inputs, CPU, ROMs, and RIOT chip... not particularly in that order Smile

JB
(james at you know what arcade dot com)


--James Bright
http://ggdb.com
http://www.QuarterArcade.com
http://tech.QuarterArcade.com
http://www.arcaderenovations.com
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