Dell Monitor has "No Power"!!

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK,,,,,with boards disconnected. The five pins that go to the second board, 1st pin 3.3V, 2nd pin 5V, #3, 4, 5 zero V. The 3 caps, #1 5V, #2 15V, #3 3.2V. Between pin #1 and #2 on IC701 5V. The two diodes on the big heat sink now show 5V, and 16V.
With the boards connected, on the 5 pins to the second board, I got .4V on the first pin and zero on 2, 3, 4,and 5. On the 3 caps, I got zero on #1, 54V on #2 (rechecked a couple times), and .3V on #3. between #1 and #2 on IC701 was still 5V. Now, I'm not sure I believe this, but the diodes on the big heat sink shows zero and 55V. There are 4 separate plug ins that go around the edge of the monitor, I guess those are to the back lights? I've had these disconnected ever since I took the monitor apart. Does that hurt anything with the voltage measurements? I see the wiring harness (bunch of wires together) going from the small board to one spot on the back of the lcd, I guess this is the the harness from the VGA board? It's been plugged in while I was testing voltage.

[budm]

Re: Dell Monitor has "No Power"!!

The picture I post on post 23, there are 10 pins on the connector between the power supply-inverter board and the main board.
Can you show us by marking the pins and to show the reading on each pin? I do not see connector with 5 pins on any of the board.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

I basically covered that in post 17
9 and 10 are 3.3
7 and 8 are 5v
5 and 6 are ground
3 and 4 are ground
1 and 2 are the dim on/off

I am trying to figure out what on the main board might be drawing so hard against the 5 or shorting it out.
I assume that's why the 17 goes to 55 which I find hard to believe it's doing

This part from post 41 doesn't sound right but may have been one miss reading
" On the 3 caps, I got zero on #1, 54V on #2 (rechecked a couple times), and .3V on #3. between #1 and #2 on IC701 was still 5V."
If 5 zeroed out at caps 1 , then it shouldn't still be at the voltage regulators pin 2

[bammbammfran]

Re: Dell Monitor has "No Power"!!

There are 4 separate plug ins that go around the edge of the monitor, I guess those are to the back lights? I've had these disconnected ever since I took the monitor apart. Does that hurt anything with the voltage measurements? I see the wiring harness (bunch of wires together) going from the small board to one spot on the back of the lcd, I guess this is the the harness from the VGA board? It's been plugged in while I was testing voltage.

The 4 bulbs do not matter
the one with all the wires does take 5 volts to the screen and could possibly have an effect if the screens board is shorted
try the voltage with this unplugged

I had mentioned unplugging it in post 39

[Tayninh55]

Re: Dell Monitor has "No Power"!!

OK guys,,,,,I told you I'm a amateur. My Bad! I have everything laying out on a table and I just realized that I had been turning the small board "upside down" when I connected the two boards together. That might explain the weird voltage. OK, I did it right this time, I think. Power board disconnected from the small board. 2 diodes on the big heat sink - 5V and 16V. Voltage on the three caps - #1 5V #2 15.9V #3 3.3V. Voltage between #1 and #2 pins on the IC701 - 5V. Voltage where boards connect. #9 & #10 3.3V, #7 & #8 5V #5 &#6 zero #3 & #4 zero and #1 & #2 zero
Now with the boards connected "the right way"! 2 diodes on heat sink 5V and 30.7V, the 3 caps #1 5V #2 3.8V & #3 3.3V. IC701 voltage between #1 & #2 pins 4.7V. Now voltage where boards connect #9 & #10 3.3V, #7 & #8 5V, #5 & #6 zero, #3 & #4 zero, and #1 3.3V & #2 1.8V Don't know why the last two pins were different when all the others were the same. Finally, I think this should be the right voltage. Sorry for screwing you guys around, but didn't realize the mistake until I started looking closer at the pins connecting the two boards

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Budm,,,,,,,,,,,,I was just assuming the the top and bottom pins connecting the boards were the same, and was just testing the top row of pins and counting each as one pin, instead of two, sorry for the confusion.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

well, flipping the board over was shorting out the 5 volts and shuuting it down
But it does not appear to have killed anything
No the issue seems to be on the pin 2 voltage of 16 volts jumping to 30 ??
"2 diodes on heat sink 5V and 30.7V, the 3 caps #1 5V #2 3.8V & #3 3.3V"
SOMETHING WRONG HERE 30.7 on diode and 3.8 on # 2 cap ???.. They should be almost identical

on the two pins that are different 1 & 2(these are supposed to be different) one is the dim and the other is on off and the on off

DID YOU EVER REMOVE THE pf801 FUSE THAT I MENTIONED in post 39 ???

[Tayninh55]

Re: Dell Monitor has "No Power"!!

No I haven't, I'll do that now.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Well, I just disconnected the pf801 on the one end,,,,,,,,retested the diodes and the 3 caps,,,,,and don't have any voltage showing.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

That fuse feeds the inverter side using the 16ish volts and shouldn't have shut down the rest of the power.
try reconnecting it

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Well Bamm,,,,,,,,,,I don't know. I soldered the end of pf801 back in the board,,,,,,,and now I still don't have any voltage on the diodes or caps

[bammbammfran]

Re: Dell Monitor has "No Power"!!

Well
You may have accidentally popped the main fuse at F601 ?
set your tester to 200 ac and check the two wires on the power plug with the blue and red wire. Should read 110-120. If it read negative, reverse your test pins. Then leave the black test lead where it is and use the red probe to check the fuse at each end.
OR, disconnect power plug and use the ohmmeter function ar 20K and probe both sides of the fuse to see if you get zero.

If the fuse is ok, there is a chance that pulling the fuse made the one diode that was showing 16 then 30 finally give out ?
Again with power unplugged
This you would take a look at with the ohmmeter with the red tester plug on the center pin and the black one one of the outer pins. If zero, it shorted out, if it builds up resistance that should not be shorted.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Yep,,,,,,,that's what happened,,,,,popped the fuse F601, juice on one end, but not on the other,

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Diodes didn't zero out when I checked them,,,,,so I guess they are ok. The fuse F601, is just a regular 120V fuse, right? Should be able to pick one up at Radio Shack.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

ok
check with an ohmmeter to make sure something serious didn't happen

again with power unplugged: Compare the end on the fuse that has no juice to the ground wire of the power plug and to whichever was the neutral pin on the power plug (if you don't remember which was neutral, just check it against both the red and blue wire to make sure the tester doesn't zero out
while at it check that diode too

[bammbammfran]

Re: Dell Monitor has "No Power"!!

fuse info should be written on the board next to the white power plug
It is also on the silver part of the fuse
I think radio shack should have these

[Tayninh55]

Re: Dell Monitor has "No Power"!!

I checked the diodes, and both still show resistance, so I guess they are ok. The actual fuse that I disconnected and reconnected also seems to be ok. The marking on the fuse that blew is T2AH250V, I'll see if our local Radio Shack might have one.

[Tayninh55]

Re: Dell Monitor has "No Power"!!

Well,,,,,,,I installed another fuse, and I have 125V ac going through the fuse but I still don't show any voltage on the caps, diodes, or regulator.

[bammbammfran]

Re: Dell Monitor has "No Power"!!

This one is being a pain !
can you post another picture of the bottom of the power supply
Maybe I can see what may have happened

[budm]

Re: Dell Monitor has "No Power"!!

OK, check and report the resistances between 1 & 2, 3 & 4. Make sure to report if it is in OHMS, K OHMS, or M OHMS as shown on your meter.