Re: My first foray into Old model TV repairs.
Hi Adrian,
I was impressed with how clean and rust free the chassis looks in the first pictures. That's good news about the tube- it's always a heart stopping moment when you see what looks like a crack in the glass!
Over the years, I've come to expect problems with the LOPT. I just now accept that as part of life with old TV's. Sooner or later I'm going to have to strip the thing down and attempt (usually successfully) to repair it.
The LOPT generates the high voltage for the CRT final anode from an 'overwind'. This consists of many turns of fine wire and usually generates 15-17 KV which is then rectified by the EHT rectifier valve.
With that sort of voltage on the windings, insulation breakdown is a common problem. This can be between the overwind and the core (which is grounded) or between the primary and the core or between the different windings. All the black crud and Nicotine that collects on the transformer tends to be conductive which makes the problem worse!
Over the years, the wax or pitch impregnation fails and moisture gets deep into the windings. This can cause failure once the transformer starts operating again.
There is very little to be gained by taking resistance measurements from the LOPT- it's fairly unlikely (but not impossible) for windings to fail open circuit. You won't detect shorted turns from resistance readings.
If you have a 'scope, you can do a 'ring test' on the LOPT which will tell you if it will function or is already faulty. It won't, of course, tell you if the insulation is going to fail when you power it up! You can also pass a controlled current through the windings to gently heat them from within to drive out any moisture over several days.
It would be interesting to see pictures of the LOPT inside the screening can to see what sort of construction it uses.
Good luck with what will prove to be an interesting project!
All the best
Nick
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