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Help with dead CRO please


Rich

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So I plugged in my cro to find the trace on screen turn very bright followed by it disappearing then an arcing sound, all very quickly.

Now I probably have the terminology wrong so please correct me, but the arcing sound seems to be coming from the HV transformer itself.

I have removed, tested and replaced the two 3055 TO-220 case power transistors.

There doesn't appear to be any visual signs of anything bad. If I remove the red wire and power it up the noise is gone, but I assume without a load the piece is not working so of course there won't be any sound but I don't know anything about the circuit. The two blue wires go to the rear of the tube.

I am guessing but hoping not that the cro is throw away.

Does anyone know how I can test what I assume to be the faulty component....the HV transformer? if that is what it is called?

Not only test but maybe someone just happens to have one lying around, yeah right, but just maybe?

 

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You will have to be have to very confident and competent with working with lethal voltages to properly diagnose this.

The red wire is the EHT wire about 1KV goes to the tripler (0/P 4.7KV).

The blue wires are the heater wires.

The brightness/intensity circuit is fairly complex.

You will probably need a HV probe.

 

 

Pages 27, 52 53.

http://www.kevinchant.com/uploads/7/1/0/8/7108231/bwd_824_001.pdf

Edited by arcadus
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I don't have a HV probe :089: nor do I know how to use one.

 

But by my description of what has happened do you @arcadus think it sounds like the HV transformer?

Why is this sound occurring?

Also, if it is the culprit, what are my chances of finding one to replace it?

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Hard to tell.

 

Be aware there will be 4.7KV around the top left of the board (tripler) until the CRT is discharged. Page 29..

 

Please don't take this as gospel as CRT faults are tricky and dangerous- best left to professionals (not me).

 

I would suspect the transformer if it was irregular and possibly an ozone smell.

You can check transformer for continuity or shorts between windings by removing it.

A more regular ticking would more likely be a short on the high voltage side or tube.

If you disconnect the red wire (careful 1.2KV) and the heater lights up, you could assume the oscillator is working.

With power off, next check diodes D422, D423 and cap. C427.

Any other diodes except tripler diodes- can't be tested properly with DMM.

Transistors...After that, it will be in depth testing voltages around the board as indicated.

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