Amplifone repair log...

ArcRevival

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Rebuilt a couple of Amplifone deflection boards the last 2 days. One worked great, one didn't.

The one that did not was a bit of a basket case and was missing a lot of parts. I thought I had everything in right and got it all put back together correctly. Or did I ?

Installed a cap kit. Installed all new voltage regulators. Hard-wired the jumpers. New X and Y pots and new resistors under them. Some new diodes that were missing. Installed the fuse holders as they were missing. Removed, stripped the harness and re-installed it. Re-flowed solder in a lot of places. Put in a bias pot that was missing. Put in the posister that was missing. That's all I can think of at the moment.
Edit : I should add that I metered every diode and transistor in circuit and they had all tested good.

Plugged it in without the HV board plugged in to test voltages and make sure the +30 and -30 was there. I had +32 and -22. Ugh.

The diodes making up the bridge rectifier tested good but I guess one could still be bad. Could be something else loading it down so I took out all of the 3716's and 3792's and powered it up for just a second( if you ever do this, do not leave it on for more than a couple seconds ) to see if it was still at -22 or if it jumped up. If it's still at -22 then it has to be something in the filter cap or bridge rectifier diodes.

It was still at -22. Hmmm........ must be a diode that seems good but isn't. Changed out the diodes on the negative side of the bridge , no change. Changed out the last thing it could be, the new filter cap. Now I had -32 !
 
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Very Interesting

Thank you for the log

Have you sourced filter caps the same size as the originals, or did you have to bend the leads a bit as they are smaller?
 
Some people think I get carried away, but I always check the new caps before I install them. You'd be surprised how many new caps are over 10% off.
 
Some people think I get carried away, but I always check the new caps before I install them. You'd be surprised how many new caps are over 10% off.

Most have 20% tolerance so that's not too surprising ;) But indeed a good idea to make this a habit while you got the ESR tester out anyway....
 
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