Quote:
Originally Posted by timmy
Changed all power supply caps now all nichicon caps big increase in the b+ but it’s still being pulled down to the point where the horizontal oscillator won’t run then it draws even more and the hot tube again red plates so on the bench this don’t happen but after I put it back in the cabinet and plug everything in this is when it happens so at this point I’ll have to sit on it for now. Baffling to say the least when the oscillator runs I have excellent hv but that’s only when I first plug it in once warm up pull plug put back in no oscillator and big draw. Oh well. The veritcle centering pot after turning more then half then it varies very little I have to think maybe it’s shorted it’s wire wound and has a 385v feed to it or possibly a shorted turn on one of the sections of the verticle output transformer got to think of everything at this point.I guess now I’m going to check voltages on the tubes.
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Good Morning:
After reviewing the posts since I was away, All I see of any significance is this
post about Horiz. Output tubes overheating.
You don't need to look anyplace else. If the 6JM6 is so overloaded that the
plates glow red then this is a problem. Max ratings for that tube are 175ma
cathode current, The tv schematic shows 120ma each tube cathode current.
I would assume around 220ma it will begin to overheat, 260ma maybe red
hot plates?? This would be a source for lowered power supply voltages. If
only 1 tube overheats that means only 1 has a problem, Possibly not the
Osc. but you have to figure it out. Cathode current readings for each tube
will show what's up.
6JM6 Specs:
https://frank.pocnet.net/sheets/127/6/6JM6.pdf
This tv uses 2 6JM6 tubes in parallel, so 2 nearly identical circuits that should
have the exact same voltages on all the tube pins - This is a place to start.
Also cathode current and screen grid currents are printed on the schematic.
You need to check them and see what's going on there.
-45V on G1's most important voltage to measure. You should check all the
parts in the Horiz Osc, & Output section, All Voltages, & Sorry to say but
at some point the wave shapes at input of 6BL8 & 6JM6's. Be sure there is
no DC component making it's way to the G1's.
I would focus my attention here. If an Osc. sometimes does not start, then
you can be sure it's not running properly when it does start, lower output,
possible misshapen signal to the 6JM6's.
I gotta go, see you later on.... Good Luck....
.