2 Dec
2014
2 Dec
'14
2:07 p.m.
On Dec 2, 2014, at 11:50 , tony duell <ard at
p850ug1.demon.co.uk> wrote:
OK, got it... What a confusing manual. It's roughly what I would expect a service
manual to be
(schematics, parts lists, some faultfinding info) but it is not well organised... Perhaps
I am spoilt
by HP and Barco manuals :-)
Good, it's not just me being dense then. :) I'd imagine it makes more sense to
somebody who has seen a lot of monitor circuits, but I have a tough time making sense of
it without some additional hand-holding.
To me IC401 looks like a sync processor/oscillator. IC402 looks like the vertical output
stage.
That's pretty much what my guess was. Some of the components south of IC401 look like
they might be something like PLL filter components, and my guess was that IC401 is
probably responsible for generating the vertical ramp. I didn't probe it beyond the DC
voltage checks mentioned by the troubleshooting chart, though, because it's a bit hard
to get to without major disassembly.
I think pin 2 of IC402 is the output, pin 4 may well
be the drive input (maybe a ramp voltage
here?
I might as well tack on a test point wire or three while it's discharged and then poke
around to see if anything ramp-like is coming out of IC401. I had assumed that the
vertical drive must be fine since I can adjust the centering of the scan line, but I
suppose that the bias circuit to the final drive transistors could still be good with the
previous driver stage being bad. And especially since you have identified a possible cross
for IC402 in your next message, so I might actually be able to replace it if it's
bad!
D404 and C410 may well be that boost circuit I
mentioned and are worth checking first.
Maybe then change IC402 if you can get one.
Sounds like a plan. I still have the fall-back plan of getting another monitor to play
Frankenstein with from Cindy or eBay, but it'll be great if I can fix the monitor that
I already have.
Page 37 of the manual recommended checking for 24VDC at pin 3 of IC402, which also
connects to the junction of D404 and C110. I probed it with my DMM at C410 since that was
easier to get to with the monitor assembled, and I did find 24V there. Next (maybe tonight
if I'm not too tired after work) I'll try probing that probably drive input to see
if IC401 is generating a ramp. If I see a ramp, then I'll try digging up a replacement
for IC402.
If any experienced monitor experts can suggest possible identities for IC401, that would
sure help! It wouldn't surprise me if it's a fairly common part monitor working
incognito in this monitor.
If I do manage to fix this beast, then I should write up what I've learned on my blog
so that maybe the next person trying to fix a similar monitor will stumble across my
notes.
--
Mark J. Blair, NF6X <nf6x at nf6x.net>
http://www.nf6x.net/