Compaq W17Q no 5v

[Mr Bill]

When you first attempt to turn this monitor on it does absolutlely nothing. I checked all the fuses and they are all 0.000 so i can rule that out. Next i checked the voltages at the plug coming off the power supply and i'm not getting +5v, i'm only getting .363v. The caps on the power supply are elite ED series. I checked evey capacitor on the power supply and i found 2 that were out of spec as per the datasheet. I did change the 2 with some used spares i have (lower esr). I'm getting 162v at the large cap.

Next i checked the PWM controller (LD7552BPS). I checked btween ground and vcc and i am not getting a shorted ohm reading. I plugged the power supply in and checked pins 3 & 7 (vcc) but my readings are in the 10v to 14v range and not stable.

I then checked the adjustable shunt regulator (AZ431AZ-EA1). Between the anonode and cathode i'm getting .571 & OL in the diode test mode on my multimeter. I plugged the power supply in and i'm getting .362v at the reference pin of the regulator.

I then checked the octocoupler (PC123). I'm sure if i'm doing this right but from the data sheet the one end has an anode and a cathode so in circuit it measures .571 & .795 so i removed it and it reads .997 & OL out if circuit. I think you need to do an led blink procedure to properly test these but i have never tried it. In circuit with the power supply plugged in i'm getting -55v on the primary side and .363v on the secondary side.

So i am unsure if the .363v readings i'm getting at the octocoupler and the shunt regulator would be my no 5v problem or the voltage fluctuations at the pwm controller. I did check the few diodes and resistors on the board and they check out ok. I also checked the Q901 power mosfet and it checks ok. And the 2 Schottky barrier rectifiers check good also.

So at this point i'm somewhat stumped. Sorry for the novel

[retiredcaps]

Re: Compaq W17Q no 5v

Sorry for the novel

1) We have no problems with quantity of information as long as it is quality information which it is.

2) What is the DC voltage across the startup cap C908?

3) Was C908 replaced?

4) Those are excellent photos, but I think we would prefer them cropped just a bit closer so the reading on the pcb is a little bit bigger to read.

[Mr Bill]

Re: Compaq W17Q no 5v

C908 was replaced. Its a 22uf 50 volt cap and i replaced it with a 22uf 50v panasonic FM (new). The voltage i'm getting is between 10 and 14 volts. Just like on the pwm controller.

Do you want/need closer photos of the power board?

[retiredcaps]

Re: Compaq W17Q no 5v

I did check the few diodes and resistors on the board and they check out ok. I also checked the Q901 power mosfet and it checks ok. And the 2 Schottky barrier rectifiers check good also.

Since you checked all the output diodes and changed the small startup cap that leaves me to guess LD7552BPS is bad even though it is not shorted.

findchips shows no stock

http://www.findchips.com/avail?part=LD7552BPS

so off to ebay. $1.76 from China with free shipping.

http://www.ebay.com/itm/260963602569

[retiredcaps]

Re: Compaq W17Q no 5v

BEFORE you order that chip, disconnect the main board and see if 5V is steady. If it is not steady, then order the LD7552BPS. If it is steady, hold off ordering because the problem could be on the main board.

[Mr Bill]

Re: Compaq W17Q no 5v

BEFORE you order that chip, disconnect the main board and see if 5V is steady. If it is not steady, then order the LD7552BPS. If it is steady, hold off ordering because the problem could be on the main board.

All my voltage readings were done with the mainboard disconnected. I was worried it would be the pwm controller. I hate soldering smd components.

Btw can you post a link to a youtube video on the smd soldering. I have the chip qwick kit but all the videos i have seen remove the chip but not putting it back on the board. I think you have posted the links before but i can't locate them at the moment (eyes aren't cooperating with brain )

Thanks

[retiredcaps]

Re: Compaq W17Q no 5v

Btw can you post a link to a youtube video on the smd soldering.

CuriousInventor makes excellent soldering videos (9 minutes)

http://www.youtube.com/watch?v=3NN7UGWYmBY

Dave Jones at eevblog has a 3 part solder video, but the SMD stuff is in part 3 (for 8 pin SMD, see about 9:10 into video)

http://www.eevblog.com/2011/07/18/ee...surface-mount/

[retiredcaps]

Re: Compaq W17Q no 5v

If you don't have a lot of experience with smd soldering, you might want to get 2 chips from China.

I haven't done any smd stuff yet. I will probably be getting a soldering station in the next 30 days or so. I have one monitor that requires removing a 8 pin smd IC.

I don't have any ChipQuik. I may try prying the legs off with a screwdriver after heating the leg. Of course, I will practice on junk boards first.

[Mr Bill]

Re: Compaq W17Q no 5v

If you don't have a lot of experience with smd soldering, you might want to get 2 chips from China.

I haven't done any smd stuff yet. I will probably be getting a soldering station in the next 30 days or so. I have one monitor that requires removing a 8 pin smd IC.

I'll order 2...I should get the chips about the same time you get your solder station