HP W2408 Problem

[PlainBill]

Re: HP W2408 Problem

There was no problem, I had a little help reading the voltmeter.

The voltage varies on that pin. From about 10-15V pretty fast.

/Christer

Bingo!!!! We are getting closer to the fault. The SMPS controller begins operation when that pin rises to 16 volts and ceases operation when it drops below 10 volts. During normal operation it should be at 20 volts. There are several possible causes, but the first suspect is the 'startup cap'. The most likely component for that is C872. I'd suggest checking the voltage across it. If it has the same behavior as pins 10-15, replace it.

PlainBill

[brunolundh]

Re: HP W2408 Problem

The voltage varies over C872, and I changed the C872, but still the same behavior with the voltage that varies but a little slower.

[PlainBill]

Re: HP W2408 Problem

The voltage varies over C872, and I changed the C872, but still the same behavior with the voltage that varies but a little slower.

Darn!! No luck with the easy fix. Now I'm going to have to think a little.

I've marked up the picture of the back of the board with a few things I want checked.

1. Disconnect the signal board and the inverter. Hook up AC power to the power supply.

2. CAREFULLY measure the voltage between the pin circled in black and the one circled in red. This may be about 166 volts, or it may be over 380 volts. In either case, it can sting a bit.

3. I have points labeled Gnd and Vout near the connector going to the signal card. What is the voltage across THESE two points?

4. I have points labeled Inverter power and GND near the connector going to the inverter. What are the voltages across those two points?

PlainBill

[brunolundh]

Re: HP W2408 Problem

2. The voltage is not stable there either. It's from just under 370V down to a little bit less than 355V. When i hear the clicking sound it goes up to 368-370V and then goes down to 353-355V in about 1-2 sec, and then a new click.
It might be the other way around and my voltmeter is slow, but i don't think so.

3. Here it's varies from from just under 8V to 5.7V and when I hear the clicking sound it goes up and then down in 1-2 sec.

4. Same thing but here i see a pattern:

1st click it goes up to about 14V
2st click to about 12V
3rd click to about 10.5V

and then back to 14V

every times it goes down to around 6.5V before every click.



I just want to thank you for all the help, I really don't know what to say .

Regards
Christer

[PlainBill]

Re: HP W2408 Problem

2. The voltage is not stable there either. It's from just under 370V down to a little bit less than 355V. When i hear the clicking sound it goes up to 368-370V and then goes down to 353-355V in about 1-2 sec, and then a new click.
It might be the other way around and my voltmeter is slow, but i don't think so.

3. Here it's varies from from just under 8V to 5.7V and when I hear the clicking sound it goes up and then down in 1-2 sec.

4. Same thing but here i see a pattern:

1st click it goes up to about 14V
2st click to about 12V
3rd click to about 10.5V

and then back to 14V

every times it goes down to around 6.5V before every click.

The usual causes for the ticking sound is a bad startup cap, or an excessive load. You've replaced the startup cap, so that's eliminated. Check the resistance between Gnd and the outputs I identified on the picture in my previous post.

I just want to thank you for all the help, I really don't know what to say .

Regards
Christer

Say 'It's Working!!!' (when it actually is.)

PlainBill

[jutt80]

Re: HP W2408 Problem

Thanks Plainbill,

I have simmilar problem with my HP W2408 Monitor. it will work for a while, next time you start the power stay yellow. Its open right now and working fine but I cam hear buziing noise from power board. Must be switching transisters. Should I replace all caps on the power board.

Thanks

Jutt80

[PlainBill]

Re: HP W2408 Problem

Thanks Plainbill,

I have simmilar problem with my HP W2408 Monitor. it will work for a while, next time you start the power stay yellow. Its open right now and working fine but I cam hear buziing noise from power board. Must be switching transisters. Should I replace all caps on the power board.

Thanks

Jutt80

Sorry, but you have a different problem. The SMPS is working on your monitor. The problem MAY be bad caps, but I'm not going to suggest replacing them until you post a picture of the top power supply board and identify the brand of the caps. Also, post a picture of the top of the signal board. Note, attach the pictures using 'Manage Attachments' - below the text entry area.

PlainBill

[brunolundh]

Re: HP W2408 Problem

The clicking sound is much lower than before but I can still hear it.

Maybe I have to order a better quality startup cap before we do anything more.
The one i put in is a cheap one I got in som kit.

2. CAREFULLY measure the voltage between the pin circled in black and the one circled in red. This may be about 166 volts, or it may be over 380 volts. In either case, it can sting a bit.

Here I get 369kΩ

3. I have points labeled Gnd and Vout near the connector going to the signal card. What is the voltage across THESE two points?

And here 11kΩ

4. I have points labeled Inverter power and GND near the connector going to the inverter. What are the voltages across those two points?

Here it is 12kΩ

[retiredcaps]

Re: HP W2408 Problem

Maybe I have to order a better quality startup cap before we do anything more.
The one i put in is a cheap one I got in som kit.

Is the cheap one used? New? What brand is it? Do you have a multimeter than can measure capacitance?

[PlainBill]

Re: HP W2408 Problem

The clicking sound is much lower than before but I can still hear it.

Maybe I have to order a better quality startup cap before we do anything more.
The one i put in is a cheap one I got in som kit.


Here I get 369kΩ


And here 11kΩ


Here it is 12kΩ

Are you measuring voltage (with the meter on the proper DC volts range) or resistance?

PlainBill

[brunolundh]

Re: HP W2408 Problem

Is the cheap one used? New? What brand is it? Do you have a multimeter than can measure capacitance?

It´s a new one. I don´t know the brand, sorry.
My multimeter do that, and I get the right value from the old cap.

[brunolundh]

Re: HP W2408 Problem

The usual causes for the ticking sound is a bad startup cap, or an excessive load. You've replaced the startup cap, so that's eliminated. Check the resistance between Gnd and the outputs I identified on the picture in my previous post.

Maybe I missunderstand what to do.
I was checking the resistance and refering what points It was by quote the old post.

/Christer

[retiredcaps]

Re: HP W2408 Problem

Are you measuring voltage (with the meter on the proper DC volts range) or resistance?

It is resistance because you asked him to measure the same points in post #45 after the voltage readings.

At first, I was totally confused and it took me a few minutes to re-read and realize what was going on.

[transonic22]

Re: HP W2408 Problem

It has been a few years since this post was revived. I too have a HP w2408h monitor that has stopped working, i have followed this post, but have different problem it seems. Here is what i know:
*I have no voltage coming from the secondary of the transformer
*There is only dc voltage showing on the primary side.
*C854 is at about 150V
*there is no ticking or any sounds of any kind coming from the board.
*there is 13.5 Volts between pins 10 and 15 on the SG6902SZ

I've learned a lot so far just from this thread, I would really like to get this monitor working again. Any help would be appreciated.

Chad

[retiredcaps]

Re: HP W2408 Problem

*there is 13.5 Volts between pins 10 and 15 on the SG6902SZ

13.5V is not enough to start the IC. The datasheet



page 7 states that 16V DC is the typical start voltage.

A likely culprit would be the start up cap may be bad. It will be the one tied to pin 15.

[transonic22]

Re: HP W2408 Problem

So i replaced all but the 3 1000uF caps on the power supply. still same issue. I did find however, that the monitor will start working if i put my multi-meter from r867 across to r866, and try to measure dc voltage. the monitor will continue to work until I manually turn it off with the power button. At which time it will not start again until I measure the dc voltage across the resistors again.
any ideas?

[budm]

Re: HP W2408 Problem

Can you show the pictures of the location of these two resistors? It can be due to the stray capacitance and the 10MOhms impedance of the meter being imposted on the circuits that causes it to run.

[transonic22]

Re: HP W2408 Problem

I circled the pairs of lead I connected my multi-meter between. It only does it with my fluke 322 meter. I have a cheap canadian tire meter that does not cause the same effect.

[budm]

Re: HP W2408 Problem

Those 4 resistors look like they are part of the AC Detect circuit that feed the Hybrid SMP PCBA (the small board that sitting up right). They should be high resistance value. Can you see the color bands on all four of them?

[transonic22]

Re: HP W2408 Problem

yes I think the resistors were supposed to be 604Kohm and 2.4Mohm i did try to measure them but my multimeter multimeter isn't all that accurate, they did seem to be in spec.
color bands were
red yellow black yellow brown
blue black yellow orange brown