02-08-2016, 01:41 PM
Yes - some Tek HT transformers do indeed develop winding shorts. Some seem to be more prone than others - the 7834 multi-mode storage scope seems to be pretty vulnerable. I have a copy of Tek's winding spec - and it is not at all trivial. Someone on the Tekscopes list managed to wind one to resurrect his 7834, and it took a while! The other thing that goes is the HT multiplier, which is something that it is also possible to repair, but the guts need to be de-potted and so is rather messy. If that goes, the trace just disappears. But the HT is around 18kV to 24kV, so it is kind of expected that every once in a decade or four it might have issues!
Alan - a specific issue with the 7704A is around the HT box at the rear of the CRT, right side as you face the screen. Take the lid off. Now Tek went through about five or six revisions of the board - because the earlier ones had a discrete resistor divider chain made of carbon composition resistors. Which in the fullness of time burns the board - and we're talking full charcoal here. Which causes the HT to fail because of the conductivity of the charcoal. I fixed one of mine by grinding out the charcoal with a dremel and conformal coating. Then I wired up the chain with new resistors dead bug in the air.
Just for laughs, I attach the 7834's HT transformer spec
Alan - a specific issue with the 7704A is around the HT box at the rear of the CRT, right side as you face the screen. Take the lid off. Now Tek went through about five or six revisions of the board - because the earlier ones had a discrete resistor divider chain made of carbon composition resistors. Which in the fullness of time burns the board - and we're talking full charcoal here. Which causes the HT to fail because of the conductivity of the charcoal. I fixed one of mine by grinding out the charcoal with a dremel and conformal coating. Then I wired up the chain with new resistors dead bug in the air.
Just for laughs, I attach the 7834's HT transformer spec
