by Rebel Rafter » Mon Nov 16, 2015 10:38 pm
Hi, folks, RR here. I have a non working Telequipment D32 scope for repair which a friend of mine got from ebay. For those not familiar it's a portable scope with ni-cad batteries, with a push-pull inverter using a pot core transformer to provide all the different voltage rails, including the EHT. I've removed the batteries as they're all original from 1972 and therefore well knackered, and I've modified the power input arrangement so the scope can run from the mains without overvoltage in the absence of the batteries. But there is no output at all from the transformer so I suspect it of having shorted turns, most likely in the EHT winding, as I can't find any shorts on the outputs or any shorted rectifiers or capacitors, etc. So I took the transformer out and thought about how I could test it without my ringing device which has gone missing. So I thought what about the "rush" from a blank FM frequency on an old ghetto blaster I've got, so I connected one of the low voltage windings of the pot core to a speaker output without the speaker connected and I connected a mains neon to the EHT output and turned up the volume and the treble and guess what, the neon lit up all nice and bright! and I got several volts from the other windings too. The audio output is about 7 watts. So does this mean the transformer is ok, or is it just giving me false hopes? I thought I'd mention this as I thought this might be a possible means of testing old TV line output transformers, though I think you'll need a few more megohms in series with your neon for testing TV LOPT's, especially colour ones. RR.