CTX 1451ES raster but no pic
 

I'm repairing this old monitor just because I don't wanna throw it away.
Strange symptoms, has HV, heater, and if I turn up the G2, a perfectly
normal looking raster, however there's no image at all when connected to a
known good source. Anyone seen this one?

Does it have an LM1203(n) RGB processor IC (look close to where the VGA
cable terminates, it's a big 24 or 28 pin package, physically similar in
dimensions to old 27xxx EPROMs)? If so, these blow regularly.

Also, if it has a 74(LS/HC/etc)08 IC biffering the sync signals from the VGA
cable (follow Hsync & Vsync path), these also blow regularly.

Otherwise, follow the RGB colour signals with a CRO, and see where they get
lost.


"James Sweet" wrote in message
news:FQled.510$LT1.179@trnddc09...
I'm repairing this old monitor just because I don't wanna throw it away.
Strange symptoms, has HV, heater, and if I turn up the G2, a perfectly
normal looking raster, however there's no image at all when connected to a
known good source. Anyone seen this one?

"Craig Hart" wrote in message
...
Does it have an LM1203(n) RGB processor IC (look close to where the VGA
cable terminates, it's a big 24 or 28 pin package, physically similar in
dimensions to old 27xxx EPROMs)? If so, these blow regularly.



It has a M51387P IC buffering the RGB signals, so far as I can tell this is
the culprit. Vcc is ok, varying voltages present at the RGB inputs, zero on
all three outputs. Anyone have one of these in a scrap monitor before I
order a new one?

I would check the voltage on the contrast pin of the M51387P.
Many IC's run near 4 volts on this pin. I would try connecting a
low voltage adjustable power supply to this pin and change the
voltage and see if that brings the video back.
I have had a couple of monitors where I had to add a resistor
between a voltage source on the board and the contrast pin in order
to supply the proper voltage and get a good video.
Hope this helps....
John


"James Sweet" wrote in message news:xZSed.3859$8R.1050@trnddc02...
It has a M51387P IC buffering the RGB signals, so far as I can tell this is
the culprit. Vcc is ok, varying voltages present at the RGB inputs, zero on
all three outputs. Anyone have one of these in a scrap monitor before I
order a new one?

IIRC I got about 5.6v at the contrast pin, are you saying I should see
around 4v? Does voltage higher raise or lower contrast?


"John Gill" wrote in message
om...
I would check the voltage on the contrast pin of the M51387P.
Many IC's run near 4 volts on this pin. I would try connecting a
low voltage adjustable power supply to this pin and change the
voltage and see if that brings the video back.
I have had a couple of monitors where I had to add a resistor
between a voltage source on the board and the contrast pin in order
to supply the proper voltage and get a good video.
Hope this helps....
John


"James Sweet" wrote in message
news:xZSed.3859$8R.1050@trnddc02...
It has a M51387P IC buffering the RGB signals, so far as I can tell this
is
the culprit. Vcc is ok, varying voltages present at the RGB inputs, zero
on
all three outputs. Anyone have one of these in a scrap monitor before I
order a new one?