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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 15th Aug 2023, 3:22 pm   #1
naujoks
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Default Sony PVM-1442QM almost dead

I have a beautiful Sony PVM-1442QM, which has developed a problem out of the blue.
When switching it on, there was a hissing sound and the power LED went from bright green to dim green after 2 seconds. No picture.
Opening up I could see no blown parts.
I swapped the power supply board from another monitor, same model, and it actually came on again.
I didn't use it for a couple of weeks and when I switched it on again today, the same symptoms as before were showing. The power supply board is good, I checked the voltages and tried it in the other monitor.
I switched on the monitor, leaving it uncovered to try and see/hear where the hissing sound is coming from, and I could see some arching and the smell of ozone (lovely!) coming from Q501 on the main board, which I think is the HOT.
I took it out, measured it through, but it seemed fine. I replaced it with a new one (2SD1397), but it didn't fix it.

Any ideas what could be responsible for those symptoms and what else I could check?
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Old 16th Aug 2023, 3:05 pm   #2
John123
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Default Re: Sony PVM-1442QM almost dead

Arcing and ozone smells are usually associated with high voltage corona discharge. Have a look around the body of the line-output transformer, the anode cable, and also the anode 'suction cup' on the tube itself. Sometimes dust can accumulate around said cup, and cause a slight arc to the aquadag coating of the CRT itself. More so if the room is damp or humid.

You might actually be able to see the discharge in a darkened room. Worst-case scenario, a split in the body of the line-output transformer itself which is then arcing to nearby metalwork.

As always, cautioned advised around these areas, and in general live areas of the chassis. If you don't have access to an isolation transformer, treat all exposed internal metalwork as mains live. Use only plastic pry tools for inspection and keep one hand in pocket, etc..
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Old 16th Aug 2023, 5:00 pm   #3
naujoks
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Default Re: Sony PVM-1442QM almost dead

I think the arc I was between the 2SD1397 and the heatsink it's attached to (it's isolated from it though).
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Old 16th Aug 2023, 6:07 pm   #4
Lloyd 1985
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Default Re: Sony PVM-1442QM almost dead

If the transistor is supposed to be isolated from the heat sink then check the insulator, if it’s one of those mica ones it may have broken down.
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Old 16th Aug 2023, 6:20 pm   #5
naujoks
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Default Re: Sony PVM-1442QM almost dead

I did check it, there's no continuity between the metal part of the transistor and the heat sink.
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Old 16th Aug 2023, 7:49 pm   #6
hans
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Default Re: Sony PVM-1442QM almost dead

It might look ok if you measure it with a DMM, but when you have some volts the insulator might start to conduct/arc.
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