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How to test High Voltage Rectifier

 
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shanghyd



Joined: 27 Apr 2006
Posts: 3

PostPosted: Thu Apr 27, 2006 3:58 am    Post subject: How to test High Voltage Rectifier Reply with quote


Can someone tell me how to test this rectifier please?
(Everything is unplugged, no power going to any components)
Thanks for the help
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awright



Joined: 10 Aug 2005
Posts: 20
Location: Oakland, California

PostPosted: Thu Apr 27, 2006 4:31 pm    Post subject: Reply with quote

Since it is a voltage multiplier made up of several lower voltage components, you should be able to test each individual component to determine general health of the multiplier.

Measure reverse and forward resistance of each diode individually without removing them or opening connections. If these diodes are very high voltage types (not likely), they may have multiple diode pellets in series inside each diode, in which case, the ohmmeter may not have a large internal battery voltage to overcome the forward voltage drop of multiple pellets. If you don't get any conductance indicated in the forward direction using your ohmmeter, try using the ammeter function (set on 10 ma), with a 1K resistor, the test diode, and a 9 volt battery in a series loop. Should get conductance indicated in one direction only.

Then measure each capacitor for leakage with the probes applying reverse bias on the two diodes paralleling each capacitor to effectively remove the diodes from the circuit (assuming the diodes tested ok.

awright.
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shanghyd



Joined: 27 Apr 2006
Posts: 3

PostPosted: Thu Apr 27, 2006 6:20 pm    Post subject: Reply with quote

Thanks for the reply.
I better give more details.
The whole unit is sealed. I can get to the wire that goes to the CRT and two posts that are sticking out of the bottom rear of the rectifier.
Actually there are four posts, one each sticking from each corner of the rectifier.
One post goes to ground, the other to the transformer and the other two seems to be there for stability.
The operational volts at the CRT are 12,000V. I haven't measured this of course, that is what is on the schematic.
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shanghyd



Joined: 27 Apr 2006
Posts: 3

PostPosted: Thu Apr 27, 2006 6:41 pm    Post subject: Reply with quote

Here's a better schematic.
The resistor R901 was fried. I mean completely burnt. I couldn't tell what colors were on the resistor it was that fried.

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awright



Joined: 10 Aug 2005
Posts: 20
Location: Oakland, California

PostPosted: Thu Apr 27, 2006 11:56 pm    Post subject: Reply with quote

Well, you can test basic functioning of the multiplier with a low voltage AC drive to the multiplier input. You should still get an output at a multiple of the input peak-to-peak voltage. I'm not sure if a 50 or 60 Hz. sine wave will do the job since the multiplier is intended to be driven by fast rise time pulses, but no harm in trying it out, since there are no transformers inside the multiplier. Try a 24 VAC transformer to supply the multiplier. The output will not be an full multiple of the input P-P voltage, since you will have all those diode voltage drops.

Not sure I can help you with the R901 problem, as I am not a TV service person. However, it looks to me that burning out of R901 would be caused by excessive load at the rectifier bridge output going out the top of the bridge. In fact, I can't even claim to understand how the bridge works in combination with the multiplier.

Good luck.

awright
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