Dell Monitor has "No Power"!!

[budm]

Re: Dell Monitor has "No Power"!!

Hmm, I do expect some voltage on that device. Can you read the number as printed on that part? I expect some kind of 1.8V or 3.3V regulator to power the processor IC on that main board.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

As I noted, I couldn't get any voltage readings at CN701, which connects the two boards together either. The numbers on the part you asked for are:

H262
952T65

[budm]

Re: Dell Monitor has "No Power"!!

OK, lets verify the voltages again.
Please report the voltage readings on those 3 caps.

[Lumberjack777]

Re: Dell Monitor has "No Power"!!

If this is a BenQ type board you need to check the fuse (picofuse) PF801 located on the bottom left center according to your picture in the first post. Rtech mentioned that in his post; but it may have been overlooked. If it's open you need to check the 4 C5707's located in the inverter section.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Budm - Voltage on the caps you mentioned: #1 was 5.00V #2 was 15.00V and #3 was 1.99V Had the range set on 20V DC.

Lumberjack777 I re-checked the fuse for continuity and it was OK.

Thanks again for everyone's help,,,,,,,,,,,but it looks like I am going to need even more!

[budm]

Re: Dell Monitor has "No Power"!!

Post 18 "BUT I CAN NOT get any voltage to show at the CN701 connector pins" Now that does not make sense since test point 3 the positive leg of the cap is connected to two pins (pin 9 and 10) of the CN701 connector.
But any way, 2V on #3 (output of IC701 LDO regulator , pin1 is Ground, pin 2 is Input, pin 3 (Big tab/center pin is Output) seems low, that 3 pin device may be 3.3V regulator, can you read the number as printed on that 3-PIN device IC701? I can see '33 ' on the body. I believe you are not getting the right voltage to run the main board. Check the 0.68 Ohm resistor (R782?) which the 5V is fed into and then the output side of the resistor is connected to the input pin of the IC 701 LDO regulator.

Pin 8 of CN701 PIN 8 is 5V which is fed from #1 cap through Inductor L702?

[Tayninh55]

Re: Dell Monitor has "No Power"!!

budm,,,,,,,,,,I'll recheck that CN701 again. When I checked it before, I put the ground lead on pins 5 & 6, and then on 3 & 4, (which I was told were grounds) while touching all the other pins with the positive lead. I had "no reading" on my meter. Next I put the ground lead on one of the chassis grounds on the board, and then touched each and everyone of the pins on that connector with no results. Maybe I'm not doing it right?

[budm]

Re: Dell Monitor has "No Power"!!

Those caps that I have you test the voltages, use one of those cap negative legs as the ground ref point for the secondary side, as you can see, the negative legs are connected to big copper traces. Or you can use the heatsink where the 2 output rectifier diodes are mounted on.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

Budm - Voltage on the caps you mentioned: #1 was 5.00V #2 was 15.00V and #3 was 1.99V Had the range set on 20V DC.

Lumberjack777 I re-checked the fuse for continuity and it was OK.

Thanks again for everyone's help,,,,,,,,,,,but it looks like I am going to need even more!

You should be getting 3.3 at the #3 capacitor
Did you check these voltages while the main vga board was connected or while it was disconnected from the power board

Since you are not getting 3.3 at cap#3
check to see if you are getting 5 volts to that LD1117L33 voltage regulator at IC701
pin 2 would be + and pin 1 would be -

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK, somethings screwy in Denmark! budm & bammbamm, I went back to try to find voltage where the two boards are connected. Put neg lead on heat sink, and positive on each of the connections (yes,,,,,the boards have been connected when I've checked the voltage) and once again, I found NO Voltage on any of those pins. THEN I went back to check the voltage that budm had requested for the 3 caps and guess what, it was different this time. I had zero voltage on the number one and number three cap, and only .04 volts at the number 2 cap. Budm, the number on the regulator is as bammbamm listed in his post, LD1117L
33AJSFA2

[budm]

Re: Dell Monitor has "No Power"!!

So it is 3.3V regulator. Please check the battery of your meter, also check the voltage of a AA battery or something like that to see what you get. Meter is set to DC, right? We cannot go any further until we are getting some consistence voltage readings from your meter.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK, I understand, will do. I had no voltage reading at the regulator between pins 1 & 2. I went back and checked #2 Cap and it started out at 15Volts, but leaked down to zero. I checked a AA battery with my meter and got 1.62 volts, battery could be older but seems to read the AA battery ok,,and yes, I've been reading on DC range. I agree with you about the voltages,,,,,,,seems like every time I recheck them they've changed.

[budm]

Re: Dell Monitor has "No Power"!!

It sounds like the power went into shutdown mode. Disconnect the main board from the power supply and check the voltages on all three places again.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK Guys, here's what I found. With the two boards disconnected I have 177V on the big Cap,,,,the two diodes on the heat sink have 5V and 15V, the three smaller caps #! has 5V, #2 has15V, and #3 has 2V. The five pins where the boards connect has 2V on the 1st pin, 5V on the second pin, and no voltage on the other three pins. I checked the IC701 and had 5V between pin #1 and pin #2. I hooked the boards together to check voltage on U6, but found when I hooked them together,,,,,,the voltages I had previously checked with the boards disconnected was at the very least cut in half,,,some more than that. So, I didn't check U6, but disconnected the boards again,,,,,,,,rechecked all the above voltages, and they were the same again.

[budm]

Re: Dell Monitor has "No Power"!!

"and #3 has 2V" without having the main board connected, that means this IC701 3.3V V reg is not working.
Then if you connect the main board back in, the voltage will drop, so it can be that the main board is drawing too much current, or the power supply is bad due to such as start up cap in the primary side.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

To start: try changing the voltage regulator at IC701and the two small green canister type capacitors that are by the smaller heatsink

voltage regulator
http://www.digikey.com/product-detai...55-1-ND/669252

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK, ordered: one of part #497-3455-1-ND Voltage Reg 3.3 volts output.
two of part #P5570-ND 47uf, 50 Volt Capacitors

Thank you very much,,,after they arrive, will see what happens!!

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK guys, I installed the two caps and the 3.3V regulator. Installed the parts. I checked the big power board, with the smaller board disconnected. I got 5V on the diode nearest the edge of the board, and 17V on the other diode on the big heat sink, same as before. When I checked between the #1 and #2 pins on the regulator, I got 5V, same as before. After I connected the two boards together, I got zero volts on the two diodes and zero volts between the two pins on the regulator, exactly the same as before I exchanged the parts. Well,,,,,,,,,,,,,,what now, the junk pile? I do appreciate your effort!

[bammbammfran]

Re: Dell Monitor has "No Power"!!

so is the 3.3 volt regulator putting out that with the boards disconnected (if I recall, it wasn't before the transplant)

if it is, disconnect the wiring harness that goes between the lcd panel and the vga board and check again.

Then if still shutting down
disconnect the black fuse at PF801 which is near the larger aluminum heatsink and test again . if you want, just remove the one end nearest the heatsink

[budm]

Re: Dell Monitor has "No Power"!!

You were getting 2V instead of 3.3V (5V input to the IC) post 34, so what do you get now with just the power supply by itself?