SB-614 problem....

[Alexander N. Gerli, Sr.]

Hi, folks!

My '614 is behaving VERY strange. While the trace is sharp, it sure isn't
right.

The vertical position and gain is right on. The horizontal ISN'T. The spot
will not go further than one-third from the left off-screen. In addition,
the horizontal gain only spreads from the spot to its left, not evenly left
and right. Trying to even the spread out using the horizontal balance pot on
the main PCB, just won't work. I can get the spot to begin spreading evenly,
but the balance pot wants to move the spot off the left side of the screen!
I've tried to reset everything using the Manual, without any success.

I've replaced the four 10k/7W sand resistors in the balance network with
10k/10W units. The original 7W resistors were about 50% high in value, so
they'd overheated with time and use.

I suspect that something in the balance circuitry is way off value, but I
don't know where to start looking. The manual isn't much help for this.
There are two 270pF disc caps to ground, one going to each horizontal anode
ahead of the axial inductors from the +180V horizontal supply. I'm presently
waiting for some 270pF/500V disc ceramics I've ordered. However, I'm just
uncertain that these two caps are the problem. Looking at the schematic, I
can't figure out what else might be a high-failure part.

I got new HV caps from Mouser - .15/2kV ones - that have plenty of voltage
overhead, unlike the 1600V original ones. BUT, the original ones were .1uF,
not .15. However, considering their use, I doubt that the change in value
there would make any difference. After all, the vertical position and gain
are right on the mark. And, there's not a trace of ac ripple on the line I
can get vertically or horizontally, so the signal (what there is of it) is
nice and clean.

Has anyone else had a problem like this, and what was your magic fix???

73, and thanks!

Sandy AC1Y
 
Alexander N. (Sandy) Gerli, Sr.
4012 Bristol Road
Durham, NC  27707-5403
(919) 489-9638
CCA #AC96-00001
 
REAL radios glow in the dark!!!!


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