Power supply problem in Sony GDM-17SE1

About 2 years ago is the last time I serviced this type of monitor. I
do not have the diagrams myself. I was doing a contract for someone
who was servicing these. You probably have some bad electrolytics in
the horiz output stage, pin amp circuits, or the powersupply.

I would not blindly change capacitors. I would troubleshoot for the
defective ones. You could end up changing a lot of caps and not the
right one. I use an ESR meter, or try substitution by tacking on
an equivelent value cap parellel to each one in suspect. The second
method mentioned here is rather tricky but works.

The powersupply has a number of output voltages. They will mostly all
effect the overall performance of the montitor. There is not just one
voltage for the horiz output stage. The highest voltage is for the
flyback output circuit including the HOT. In most monitors it is
about 130 to 160 volts depending on the design.

Your interference can be comming from a decoupler cap in one of the
video stages, or from a bypass cap in the secondary supply side from
the flyback outputs. There is also a chance that a bad cap in the
powersupply can cause this problem as well...

If you can scope the powersupply outputs and the flyback secondary
outputs, you will see right away if there is noise on its outputs.
Use a 10X probe when doing this.

The pin distortion would be hard to spot unless you knew the exact
waveform specs to look for at their respective TP's.

--

Jerry Greenberg


Email:
Home Page: #
Components: #
Products: #
Navigation: #
Sci/Inst: #
Personal: #

Electronic Components, And Navigation Compasses

Message Separator


Hi all,

I have this HP monitor (A4032A) that's an OEM version of the Sony
GDM-17SE1.

I'm having the following problem: The horizontal stage's geometry is
weird, there's a bow that changes as the monitor warms up. There's
also
some interference noise in the image which also tames down as it warms
up.

The usual suspects are the electrolytics in the power supply. I used a
variac to reduce the line voltage, and the bow and interference are
greatly affected by lower input voltage. So I have the following
questions (mostly for someone who has seen the innards of this beast
before):

1) Should I just replace caps in the power supply module?

2) What power supply feeds the horizontal circuit anyway? (don't have
the schematics... :( )

3) Is there a voltage regulator here that I'd be better off replacing?

Thanks much.

Mig