Ray Carlsen wrote:

Vertical circuit: this monitor uses discrete components (no ICs). The
output
transistors are Q304 2SC2073 and Q305 2SA940. Note that this monitor
has a
service switch in the center of the bottom board toward the left
side. That
switch should be in the NORMAL position. If in SERVICE, the vertical
sweep
will collapse to a single horizontal line (used for CRT setup
adjustments).

OK, an update on this situation. Remember that the display on this
monitor slowly collapsed over a period of 2-3 weeks to a thin line
across the center of the screen.
Investigating the circuitry I found that the two transistors Ray
mentions, above plus Q303, all show evidence of soldering indicating
they have been replaced in the past. I got new parts - original part
number for Q303 (2SC2230) and NTE crosses for Q304 and Q305. This did
not fix the problem. The old transistors all appear to check out OK on a
Fluke meter diode test.
Using the NTE cross datasheet for the TA7644 IC (
http://www.nteinc.com/specs/1500to1599/NTE1547.html ) I looked for the
Vertical Drive Output on pin 26. There is no signal there, just a 0 VDC
level. I have a ramp signal running on pin 28, the Ramp Capacitor pin.
With the scope synced on Line this is rock steady. There is another ramp
signal on pin 27 but it drifts a bit compared to line sync. I have 12
volts on Vcc at pin 3 so the chip is getting power.
I don't know if it's significant but pin 31, Vertical Sync Input, is
at 0 VDC. I didn't have a video source connected to the monitor so
perhaps that's normal? Unfortunately, we don't have any video sources in
the service area at work so it's hard to supply one for troubleshooting
purposes.
I have worked in electronics for many years but video circuits are
like a foreign language to me.

--

Rick Jones
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"If God had meant us to vote, he'd have given us candidates."
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