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Old 05-14-2005, 10:58 AM
zacster
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I've replaced all the caps...

in my DuMont RA112, and the chassis is on the bench in the basement and the rest of it is upstairs. I'm going to re-check all of my work against the schematic for continuity and shorts as much as possible, and I've already done that as I've gone along without finding anything out of order. I've got a table of resistance readings to check the tube pin sockets against. I've got a 2' by 4' blowup of the schematic, and the rest of the Sams folder on this set.

Question 1. When checking resistance, do I do this with the tubes in or out? When I built my pre-amp, the instructions were with the tubes out, but there are a lot more tubes in this TV.

Question 2. Assuming 1 above checks out, do I plug it and bring it up slowly with a variac inside the cabinet with the picture tube and everything else connected, or do I bring it up on the bench, being careful with the connections that they are not touching anything else, to make sure I'm not going to smoke it first, then put it all back together.

Question 3, big safety question. Once I've applied power to the chassis, I know enough to discharge the electrolytics before working on it again, but I've also been reading on the picture tube capacitance. As I understand it, you want to discharge the picture tube HV+ to ground on the tube itself, not the chassis. What size/wattage resistor should I use there, will it make a noise when I do this? Should I attach a wired resistor to a big stick and stand back when I do this. (I'm only half kidding here.)

Question 4. I haven't replaced any resistors, should I? I know that the high ohm tend to drift. Will the resistance check show this? Maybe I should order a bunch from Mouser.

Question 5. If the picture tube works (still untested), but I still have problems, what next? I know how to replace things, but beyond replacing tubes that might be bad I know nothing about using a scope to diagnose or do alignments. Anybody in the NYC area?

I know this is a lot of questions, but I don't have anywhere else to turn. I wish I had a digital camera so I could post pictures of what I have, and the repair job I'm doing. Other than 50+ years of dust, this thing is clean, and all the wiring still checks out.

Thanks in advance for all your help.
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