Quote:
Originally Posted by Electronic M
Sounds like you are seeing what is called 'retrace lines'. The set is supposed to turn off the electron gun when it is in between scanning different scan lines or frames (via a 'blanking circuit'), but some sets don't have that circuitry (I can't see that being the case for a Dumont though), and others it is either insufficiently designed not working due to bad components.
BTW if you play a VHS tape or DVD that has macrovision copy protection on it then that will partially disrupt the blanking circuit and place a series of bright dashes on screen.
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Thank you! I'll have to take a look at the schematic and see if I can identify the circuit you mention. I was watching a VHS tape, I'll have to take a look and see if it had macrovision. I remember it being a problem with some VCR/TV setups even back in the day when VHS was king. We had to constantly fiddle with the tracking trying to get rid of what looked like interference.
One thing that WAS an improvement today was that I switched around the three 6SN7GT tubes. One is vertical oscillator, one is vertical amp, and one is horizontal AFD/horizontal amp. I noticed that if I "flicked" one of them with my finger, the picture would jump. That seemed to happen to one particular tube no matter what position it is in. Moving it seemed to fix the top of the picture on the CRT "bending"..could be coincidence. Seems like one of the 6SN7GT tubes might have an issue, so I'm going to look around for a few NOS to buy.