On Fri, 14 Oct 2005 09:40:32 -0400, T o d d P a t t i s t
put finger to keyboard and composed:

Franc Zabkar wrote:

What voltage are you measuring on pin 13? Is it significantly higher
than pin 8? If not, then you will be running out of headroom. I'd
replace D4E2 just in case. A 1N4007 should be OK. I'm also curious as
to where the LH trace at pin 9 goes.

I had no chance to work on this yesterday, but in the 5
minutes this morning before heading out, I quickly put the
scope on pin 13 (vertical drive) and on the 30V supply which
connects directly to pin 8. The 30V supply/pin 8 looks
reasonable - a bit of ripple, but no more than 5%, perhaps
less.

Then I looked at pin 13. It looks like a 5% on duty cycle
30V signal - 95% of the time off! That would mean I'd be
looking at a 30V drop on forward biased D4E2. Whatcha think
- time to replace it? :-) Seems reasonable to think it blew
when the IC blew, and the vertical drive is somehow coming
via pin 8 instead of pin 13.

My memory is hazy, but I do know that I once had an obscure problem
that was cured by replacing this diode in another set. I'm sorry but I
can't recall if I observed the waveform on a scope. I'm still puzzled
by the trace going to the left. It doesn't appear in the application
diagram in the datasheet.

-- Franc Zabkar

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