+5V going to zero then up again on Xenon vocalizer board

AE35

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+5V going to zero then up again on Xenon vocalizer board

Hey all!

I'm still trying to fix the sound on my Xenon. I'm testing the +5 V on the
vocalizer board, and it shifts between +5V and 0V every couple of minutes.

It'll go up to +5V then quickly drop to 0V...a minute or two after it'll do the same
again. I've trying pressing stuff on the board, and the ribbon cable, but it doesn't
SEEM to be anything in a connection, like a loose socket or anything.

Are there any component that could cause this?

Thanks for your help!:)

Nicholas
 
your caps have most likely failed

great plains electronics has the cap kit for the vocalizer boardset

Pull the power connector and put your meter on the incoming +5vdc and see if it is bouncing down to zero

I don't have my manual handy, so I can't give you exact pin locations right now.
 
Hi !

Well, the voltages on the connector are stable!

So something on one of the sound boards are making the +5 voltage go all the
way up, then all the way down again over and over..

By the way, the voltages on the testpoints on the Sound Plus board are OK.

Thanks!

Nicholas
 
Hi !

Well, the voltages on the connector are stable!

So something on one of the sound boards are making the +5 voltage go all the
way up, then all the way down again over and over..

By the way, the voltages on the testpoints on the Sound Plus board are OK.

Thanks!

Nicholas

this pretty much tells you that you have bad caps
 
But I changed the electrolytic caps on the board....

Should I also change the disc caps?

Thanks!
 
If a capacitor were causing that kind of voltage drop I would expect smoke to be pouring out of it.

I'm not 100% sure I'm understanding your problem but if you're saying the +5VDC on the vocalizer board is intermittent the first thing I would look at is the 7805 voltage regulator and the 3 diodes behind it. Start by checking for bad solder joints at CR1, CR2, CR3 and Q1 (7805). If you don't find any I would wait until the +5VDC drops out and check your way through the voltage regulator circuit. See if there's voltage into the regulator but not out. If that's the case then the regulator is going open intermittently. If there's no voltage at the input of the regulator you know one of the diodes behind it is going open. Look at the schematic and you'll get the idea.
 
Hey!

Yes, the +5V is intermittent, it's either +5V or 0V

The diodes are OK, I changed them when I got the machine.

Well, maybe the 7805 is bad....I know I have one or two lying around from fixing
a NES some time ago.

Thanks!!

Nicholas
 
Sounds like a cold solder joint on one of the regulator legs or a flaky regulator.
 
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