I have a Compaq s910 which works fully except for a clicking sound from it
when the monitor enters standby mode. What I know so far is that the
clicking is just the degauser relay (nothing arcing). The monitor can only
enter standby mode for a split second before powering up the transformer
and tube etc, then a split second later goes back to standby mode and
repeats the process forever.

There is a IC (3843B) on the board which is cauing the main transformer to
kick in, but don't know if its the problem or just a side effect. I have
measured voltages from around the place and firstly have to say that I
don't understand how the aforementioned IC can even function in that AC
enviroment.

I have got the schematics for everything. The important bits:

http://members.iinet.net.au/~quadfour/3842B-3843B.pdf - IC schematics
http://members.iinet.net.au/~quadfour/s1494-1.pdf - s910 PSU schematics
http://members.iinet.net.au/~quadfour/temp.jpg - shows some voltages
I've found.

The schematics of the 3843B mentioned voltages well below the ~140AC I am
seeing on its side of the transformer. Together with that I don't have a
solid grasp on this (enough to replace components).

Any ides on how to pinpoint the reason for the 3843B turning everything on
after a split second of the monitor being in standby mode?

Cheers
Michael

What type of logic do you get on the standby input to the supply? I would
be looking farther back. The IC you are showing appears to be the driver
device for the switching supply.

The supply is probably listening to whatever is telling it to cycle when it
is supposed to be staying in standby. I would look at the circuit area that
responds to generate the standby command logic.

In many older monitors I have had defective caps in various areas cause
these types of faults. About 90% of the various faults are created by caps
going too high in ESR.

--

Jerry G.
======


"Michael Collard" wrote in message
news I have a Compaq s910 which works fully except for a clicking sound from it
when the monitor enters standby mode. What I know so far is that the
clicking is just the degauser relay (nothing arcing). The monitor can only
enter standby mode for a split second before powering up the transformer
and tube etc, then a split second later goes back to standby mode and
repeats the process forever.

There is a IC (3843B) on the board which is cauing the main transformer to
kick in, but don't know if its the problem or just a side effect. I have
measured voltages from around the place and firstly have to say that I
don't understand how the aforementioned IC can even function in that AC
enviroment.

I have got the schematics for everything. The important bits:

http://members.iinet.net.au/~quadfour/3842B-3843B.pdf - IC schematics
http://members.iinet.net.au/~quadfour/s1494-1.pdf - s910 PSU schematics
http://members.iinet.net.au/~quadfour/temp.jpg - shows some voltages
I've found.

The schematics of the 3843B mentioned voltages well below the ~140AC I am
seeing on its side of the transformer. Together with that I don't have a
solid grasp on this (enough to replace components).

Any ides on how to pinpoint the reason for the 3843B turning everything on
after a split second of the monitor being in standby mode?

Cheers
Michael

On Sat, 05 Mar 2005 08:57:28 -0500, Jerry G. wrote:

What type of logic do you get on the standby input to the supply? I would
be looking farther back. The IC you are showing appears to be the driver
device for the switching supply.

The supply is probably listening to whatever is telling it to cycle when it
is supposed to be staying in standby. I would look at the circuit area that
responds to generate the standby command logic.

In many older monitors I have had defective caps in various areas cause
these types of faults. About 90% of the various faults are created by caps
going too high in ESR.

So far I am testing as many caps as I can desolder. I can see all of them
and they look fine and undisturbed, and tested about 80% so far, all
fine. I was able to test that there is a 1V jump (on ~148VAC) at R813
(near the FET thing) and also at R814 when this was IC was turning the
transformer back on.

I don't understand how the 3843B decides whether to turn on the
transformer or not... or how its functioning in this circuit anyway. Could
I ask you to explain a little more since it looks like the caps aren't the
cause...

Cheers
Michael

Going from memory, if I am right, I no longer have the links to the
schematic, that I saw the other day.

All of these monitors, and TV sets use a uPC that runs on a firmware program
to operate the unit. It sends a shut down, or startup command to the power
supply to tell the supply to work or not. I sort of remember seeing an input
to the supply for this type of control. Trace it back, and it should end up
at a control circuit, that is commanded by the uPC.

I hope you are testing the caps with an ESR meter, and not an ohm meter, or
a standard cap meter. The ESR rating is extremely important. A cap can test
good with a cap meter, and its ESR can be too high. When using an ESR meter,
you do not have to remove the cap from the circuit board in most cases.

If you do a search on Google about Capacitor ESR, there are many
explanations to a good detail of what this means. I have had high ESR caps
in monitors and TV sets causing what you are having with yours.


--

Jerry G.
=====

"Michael Collard" wrote in message
news On Sat, 05 Mar 2005 08:57:28 -0500, Jerry G. wrote:

What type of logic do you get on the standby input to the supply? I would
be looking farther back. The IC you are showing appears to be the driver
device for the switching supply.

The supply is probably listening to whatever is telling it to cycle when
it
is supposed to be staying in standby. I would look at the circuit area
that
responds to generate the standby command logic.

In many older monitors I have had defective caps in various areas cause
these types of faults. About 90% of the various faults are created by caps
going too high in ESR.

So far I am testing as many caps as I can desolder. I can see all of them
and they look fine and undisturbed, and tested about 80% so far, all
fine. I was able to test that there is a 1V jump (on ~148VAC) at R813
(near the FET thing) and also at R814 when this was IC was turning the
transformer back on.

I don't understand how the 3843B decides whether to turn on the
transformer or not... or how its functioning in this circuit anyway. Could
I ask you to explain a little more since it looks like the caps aren't the
cause...

Cheers
Michael

Hello.

I got a compaq S910 from a friend, its manuf in 2000 and has the same
symptoms: standby click power on/off (with blinkin led) and sometimes
it just wont turn on from the power button, I can hear a very faint
tick inside and then randomly 30sec-5min it goes KA-BOING and turns
on :lol:

As it is, the monitor is useless since I dont want to keep a
fire-hazard inside my house or anybody elses.

I already sent the darn thing to a tv repair shop and the guy said
there wasnt any problems. So I got it home and it wouldnt turn on and
then when it did, I turned off the pc and the standby click was there.


Did the original poster manage to fix this? I'm about to give up on
this, getting tired of hauling its heavy *ss around.

The failure to come on is caused by the controller UC3843 (IC801) not
having its startup voltage. This is derived from the chain C843,
C844, R100 and D822. In my case C843 had lost its capacitance.
Eventually, due to the leakage through it the monitor will start up
after a long wait. I don't know yet if this solves the clicking
standby fault, but it very well may be. I fixed it by removing C843
and C844 and replacing it with one of those EMC capacitors. The value
is not very important, should be around 0.5 uF but in my case was 0.15
uF/275 VAC. The display started up happily after this. It has a very
crisp picture, so I'm happy now!

Steven

I don't know yet if this solves the clicking standby fault, but it
very well may be.
No, it didn't. But I don't care anyway for that function so someone
else can tackle that. TNX BTW to Michael Collard for the schematics!
Without those it would have been a lot harder to fix it. I may not
even have started the repair

It is kinda weird though that these two faults seem to go together...