[TechAssist] TTX 1556 monitor pulsing on and off
- From: Gary McCartney <gary@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Mon, 12 May 2003 14:30:42 -0400
This is a TTX computer monitor model TTX 1556. I have schematic for an
AOC model D556P which is very close although not 100% the same. This
schematic is dificult to read so it is of limited use to me. Actually,
there is a sticker on the CRT which has this number: D556PEAKTTD so it
appears as though the TTX and AOC must be common origin.
The monitor comes on for a few seconds, sometimes long enough to see the
data on the screen, then it shuts off and pulses back on once about
every 5 seconds. The B+ to the 3842 PWM driver IC in the power supply is
at 16.5V. If I increase this B+ to 18V via the trim pot, then the hor.
drive doesn't totally quit when it shuts off, it just changes to a
faster pulse with less HOT collector amplitude (approx. 700V p-p ratyher
than 1000 V p-p while unit is running. Just the picture goes black and
the green power indicator LED pulses. The HOT collector B+ is 74Vdc. The
output pulse from the 3842 also does not shut down when picture goes
off, but rather changes to faster pulse.
I have changed the 3842 IC along with some electro caps nearby it and I
have changed zeners ZD902 and ZD903, plus 3 timing caps off the 3842. I
am wondering if this monitor is going into a protection mode but I can't
figure what it is protecting from when the picture does come up normal
and the HOT waveform looks nice and clean and 1000V p-p. I have gone
over some solder connections on the main board.
Thanks for any help.
--
Gary McCartney
McCartney Electronics
7134 Fife Rd, RR 7
Guelph Ontario Canada N1H 6J4
Fax: (519)821-1530
email: gary (at) number63.ca
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