Hi,

I have one of these monitors which has an "unusual" fault. It appears that
the position of the start of each scan line is being modulated by a sine
wave. The period of the sine wave is "a few scan lines" and amplitude is a
few pixels worth. i.e. A vertical line appears as a wiggly line. When it is
first turned on the image is fine but it quickly deteriorates (within a
couple of minutes) going through an unstable period between working OK and
the fairly stable sine wave becoming established. Half a can of freezer
spray has not indicated that the problem is temperature sensitive (similarly
gentle heating doesn't obviously make the problem worse) - thus I'm starting
to suspect the breakdown of an electrolytic cap. I assume a PLL is
responsible for horizontal synchronisation and I'm wondering if perhaps that
one of the supply decoupling caps for the PLL has failed.

Has anybody seen this fault before or have any good ideas?

Unfortunately I don't have access to the schematics and it would be a shame
to chuck it in the skip as it's otherwise fine.


Cheers

Rob

I have one of these monitors which has an "unusual" fault. It appears that
the position of the start of each scan line is being modulated by a sine
wave. The period of the sine wave is "a few scan lines" and amplitude is a
few pixels worth. i.e. A vertical line appears as a wiggly line. When it
is
first turned on the image is fine but it quickly deteriorates (within a
couple of minutes) going through an unstable period between working OK and
the fairly stable sine wave becoming established. Half a can of freezer
spray has not indicated that the problem is temperature sensitive
(similarly
gentle heating doesn't obviously make the problem worse) - thus I'm
starting
to suspect the breakdown of an electrolytic cap. I assume a PLL is
responsible for horizontal synchronisation and I'm wondering if perhaps
that
one of the supply decoupling caps for the PLL has failed.

Has anybody seen this fault before or have any good ideas?

Unfortunately I don't have access to the schematics and it would be a
shame
to chuck it in the skip as it's otherwise fine.



I should add that on the back of the monitor the part number is:

A902MT

Cheers

Rob

I have one of these monitors which has an "unusual" fault. It appears that
the position of the start of each scan line is being modulated by a sine
wave. The period of the sine wave is "a few scan lines" and amplitude is a
few pixels worth. i.e. A vertical line appears as a wiggly line. When it
is
first turned on the image is fine but it quickly deteriorates (within a
couple of minutes) going through an unstable period between working OK and
the fairly stable sine wave becoming established. Half a can of freezer
spray has not indicated that the problem is temperature sensitive
(similarly
gentle heating doesn't obviously make the problem worse) - thus I'm
starting
to suspect the breakdown of an electrolytic cap. I assume a PLL is
responsible for horizontal synchronisation and I'm wondering if perhaps
that
one of the supply decoupling caps for the PLL has failed.

Has anybody seen this fault before or have any good ideas?

Unfortunately I don't have access to the schematics and it would be a
shame
to chuck it in the skip as it's otherwise fine.



I should add that on the back of the monitor the part number is:

A902MT

Cheers

Rob

Use an ESR meter, and test all the caps in the scan amplifier and power
supply sections. You will probably find a fair number of caps that have
gone out of specs. If you have to spend a lot of time on it, and the
monitor is more than about 3 years old, I would consider a new one. They are
very low in cost now.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Rob Whitton" t wrote in
message ...
Hi,

I have one of these monitors which has an "unusual" fault. It appears that
the position of the start of each scan line is being modulated by a sine
wave. The period of the sine wave is "a few scan lines" and amplitude is a
few pixels worth. i.e. A vertical line appears as a wiggly line. When it is
first turned on the image is fine but it quickly deteriorates (within a
couple of minutes) going through an unstable period between working OK and
the fairly stable sine wave becoming established. Half a can of freezer
spray has not indicated that the problem is temperature sensitive (similarly
gentle heating doesn't obviously make the problem worse) - thus I'm starting
to suspect the breakdown of an electrolytic cap. I assume a PLL is
responsible for horizontal synchronisation and I'm wondering if perhaps that
one of the supply decoupling caps for the PLL has failed.

Has anybody seen this fault before or have any good ideas?

Unfortunately I don't have access to the schematics and it would be a shame
to chuck it in the skip as it's otherwise fine.


Cheers

Rob

Use an ESR meter, and test all the caps in the scan amplifier and power
supply sections. You will probably find a fair number of caps that have
gone out of specs. If you have to spend a lot of time on it, and the
monitor is more than about 3 years old, I would consider a new one. They are
very low in cost now.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Rob Whitton" t wrote in
message ...
Hi,

I have one of these monitors which has an "unusual" fault. It appears that
the position of the start of each scan line is being modulated by a sine
wave. The period of the sine wave is "a few scan lines" and amplitude is a
few pixels worth. i.e. A vertical line appears as a wiggly line. When it is
first turned on the image is fine but it quickly deteriorates (within a
couple of minutes) going through an unstable period between working OK and
the fairly stable sine wave becoming established. Half a can of freezer
spray has not indicated that the problem is temperature sensitive (similarly
gentle heating doesn't obviously make the problem worse) - thus I'm starting
to suspect the breakdown of an electrolytic cap. I assume a PLL is
responsible for horizontal synchronisation and I'm wondering if perhaps that
one of the supply decoupling caps for the PLL has failed.

Has anybody seen this fault before or have any good ideas?

Unfortunately I don't have access to the schematics and it would be a shame
to chuck it in the skip as it's otherwise fine.


Cheers

Rob