Dell E173fpf - No led coming on

[quattro alex]

Re: Dell E173fpf - No led coming on

OK I ordered a SG6841 and it arrived this morning. I've started desoldering the old one using (Weller WHS40) flux and braid but I can't seem to get the chip off. I've tried with a chisel tip ~2mm wide set at 300c and also a pointed tip . I've tried to solder on a wire to help me lift one side but this didn't work.

I've even tried a copper strand around the legs to pull gently whilst desoldering, but now a small section of this is stuck to the heel of the legs. Any suggestions how I can get this chip off?

[retiredcaps]

Re: Dell E173fpf - No led coming on

OK I ordered a SG6841 and it arrived this morning.

Wow, that was quick. BEFORE installing the new one, can you do the same resistance checks on new IC "out of circuit" to see if GND is shorted to the other pins? I'm particulary interested in pin 6.

For desoldering, try

http://www.infidigm.net/articles/solder/#desoldering

[quattro alex]

Re: Dell E173fpf - No led coming on

Current SMPS in circuit
1-2 = 78.2K
1-3 = 30K-->130K+
1-4 = 26K
1-5 = open
1-6 = 41ohm
1-7 = 90ohm --> open
1-8 = 172ohm -->open[/QUOTE]

New SMPS out of circuit

1-2 =79.2k
1-3 = 190ohm --> open
1-4 = 190ohm --> open
1-5 = 148ohm --> open
1-6 = 130ohm --> open
1-7 = 110ohm --> open
1-8 = 166ohm --> open

For desoldering, try

http://www.infidigm.net/articles/solder/#desoldering

Cheers I'll give this a go once you've checked over these values

[retiredcaps]

Re: Dell E173fpf - No led coming on

Current SMPS in circuit
1-6 = 41ohm

New SMPS out of circuit
1-6 = 130ohm --> open

Okay, so I did some soldering today, but used my little PC fan to blow away the fumes. However, I still could be affected.

If the new IC pin 1-6 is infinite resistance, then that implies that the old IC is definitely shorted. Once you remove the old IC, measure it out of circuit to verify. It should read the same unless you damage it during removal.

[quattro alex]

Re: Dell E173fpf - No led coming on

Thanks retiredcaps I will give this a go in the morning. Hope the fumes wear off soon!

[budm]

Re: Dell E173fpf - No led coming on

"1-6 = 130ohm --> open" What does it mean? 130 Ohms one way with the probe, and open when you reverse the probe, just try to figure out the reading.

[retiredcaps]

Re: Dell E173fpf - No led coming on

"1-6 = 130ohm --> open" What does it mean? 130 Ohms one way with the probe, and open when you reverse the probe, just try to figure out the reading.

My guess is that he has 2 second per update speed multimeter and it takes a while to get the "correct" ohms reading.

For retiredcaps' bonus points, post a picture of your multimeter.

[quattro alex]

Re: Dell E173fpf - No led coming on

"1-6 = 130ohm --> open" What does it mean? 130 Ohms one way with the probe, and open when you reverse the probe, just try to figure out the reading.

When I put the leads onto the pins it gave me 130ohms initially and then about 1-2 secs later it went to open.

Ok so this is the title of the DMM that I used: Laser 3534 Multi Meter/temp Tester - Digital

I also have a more advanced multi meter Sealey TA 202 - I haven't tended to use this as there were concerns over it's accuracy which came about when I didn't know much about testing capacitance. Basically I used it on a live (hot) cap and now it doesn't read capacitance, also I am not entirely convinced of the DC voltage readings - these jump up and down a lot. I am going to post it on here at some point. Anyway the resistance readings seem to be ok here they are:

New SMPS (out of circuit): Current SMPS(in circuit)

1-2 78.5k 0
1-3 34.72Mohm 0
1-4 11.90Mohm 0
1-5 11.86Mohm 11.78Mohm
1-6 11.70Mohm 47.4ohm
1-7 15.20Mohm 239.3k
1-8 92.2K 93.4k

Pins 1-2 to 1-4 I believe are 0 resistance because I have a small copper wire which is contacting all the pins on this side when I tried to remove this from the board.

[quattro alex]

Re: Dell E173fpf - No led coming on

For desoldering, try

http://www.infidigm.net/articles/solder/#desoldering

This technique worked well and I removed the copper strand, but I am not sure how much heat went into the chip (it wasn't smoking). Old chip out of circuit values as follows:

1-2 80k
1-3 0.476Mohm
1-4 1.606Mohm
1-5 11.28Mohm
1-6 11.09Mohm
1-7 13.90Mohm
1-8 96K

Here's a close up of U850's location and the pads - I may need to clean some of those pads up a bit more? Use pointed tip for this?

[quattro alex]

Re: Dell E173fpf - No led coming on

Ok so I've got the new SMPS at U850 soldered in and now there is no ticking, but also no led lit up. C857 gives a more consistent voltage across it ~12 -~14v . C854 is sitting happily at 340v dc.

Next I put the inductor (L853) back in and tested - no ticking

Lastly put the resistor (R870) leg back in, tested - now its ticking like before.

Throughout the testing the board has not been connected to the chassis or the screen, would this make a difference?

[budm]

Re: Dell E173fpf - No led coming on

Ok, R870 is the fusible resistor which is used to supply the voltage to the logic board, that is why the LED does not light up. So the logic board is drawing too much current so it the power supply goes into shutdown again, the inductor is for the ground return for the inverter circuits.
Now we need to find out where the shorted circuits are in the logic board section.
You do not need to hook up the ribbon cable to the LCD panel, but you should have the lamps connected to the board.

[retiredcaps]

Re: Dell E173fpf - No led coming on

Ok so this is the title of the DMM that I used: Laser 3534 Multi Meter/temp Tester - Digital

One retiredcaps' bonus point awarded for the picture. The Laser 3534 is a rebadged version of some generic brand multimeter.

http://handsun.en.made-in-china.com/...-HM-838L-.html

I also have a more advanced multi meter Sealey TA 202. I am going to post it on here at some point.

Start a new thread for that one in

"Test Equipment Usage, Techniques, and Reviews"

and I'll try to help out.

I have some more suggestions, but need to run off now. To be continued unless you find the problem before I get back.

[quattro alex]

Re: Dell E173fpf - No led coming on

Now we need to find out where the shorted circuits are in the logic board section.

Am I right in thinking that the logic components are right side of the Resistor I lifted the leg on?

You do not need to hook up the ribbon cable to the LCD panel, but you should have the lamps connected to the board.

Thanks i'll give this a go.

I have some more suggestions, but need to run off now. To be continued unless you find the problem before I get back.

Thanks for all your help so far - I feel like I am learning a lot already. Once I've got this one fixed I have my old Philips monitor to fix (2 secs to black issue)

[retiredcaps]

Re: Dell E173fpf - No led coming on

Am I right in thinking that the logic components are right side of the Resistor I lifted the leg on?

Correct.

Suggestions.

1) Check U801, U802, and U851 for shorts. For U801 and U802, you can do a simple resistance check between all 3 pins to see if they are shorted. Measure the resistance between pins 1-2, 1-3, and 2-3.

2) For U851, find its datasheet and measure the resistance between each pin and GND.

3) See if D857 is shorted.

4) Check Q501, Q502, D303, D304, D305, D306.

5) Check D854 and D855 (back on power board).

6) If none of the above are obviously shorted, I have another list.

[retiredcaps]

Re: Dell E173fpf - No led coming on

Once I've got this one fixed I have my old Philips monitor to fix (2 secs to black issue)

Start a new thread for the Philips, but to give you a head start

2 seconds to black can be

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

More details starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

Also, see budm's Inverter tester using old CFL

https://www.badcaps.net/forum/showthread.php?t=19987

[quattro alex]

Re: Dell E173fpf - No led coming on

U801
1-2 0.960K
1-3 0.964K
2-3 2.106K

U802
1-2 0.382K
1-3 0.960K
2-3 1.344K

U851 aka AC '1506-50'
GND= pin 3
3-1 2.1ohm
3-2 0.972K
3-4 0.970K
3-5 0.000

D857 (MM48 K34) - Diode mode = 0.53v one way reversed = 0.134v

Q501 (A1AE27)

G-D O.L
D-S 0.920Mohm
G-S 0.466K

Q502 (W1A)

B-E 19.40Mohm
B-C 19.30Mohm
E-C 0.830K

Q201 (W1A1 4d)

B-E O.L
B-C 17.76Mohm
E-C O.L

Q202 (W1A1 4d)

B-E O.L
B-C 12.38
E-C O.L

D854
1-2 0.00
1-3 0.00
2-3 0.00

D855 (43A) Diode mode

Test 1 w/ Sealey TA202 DMM
0.664v correct way
0.785v reversed

Test 2 w/ Laser DMM
777 correct way
O.L reversed

[budm]

Re: Dell E173fpf - No led coming on

The D854 does not make sense:
"D854
1-2 0.00
1-3 0.00
2-3 0.00"

It is showing all shorted, but you indicated that you do get the output DC voltage with the load disconnected, then the inverter is connected back, the voltage is still OK, but when the resistor for the Logic board is connected to the power supply output, the power supply would go into ticking mode again.
This D854 is the main rectifier Diode with common Cathode (2 Diode in one package).

[quattro alex]

Re: Dell E173fpf - No led coming on

Hi Budm - when I tested the original D854 SRF10-10 it also showed as shorted on all pins. Is something in circuit causing this. I was also quite careful when soldering in the new one as these are more sensitive to heat than caps?

The other thing I am wondering is the original had a plastic body whereas the replacement has a metal back and it's code is MBR10100CT. Is this replacement wrong?

[selldoor]

Re: Dell E173fpf - No led coming on

D855 (43A) Diode mode

Test 1 w/ Sealey TA202 DMM
0.664v correct way
0.785v reversed

Test 2 w/ Laser DMM
777 correct way
O.L reversed

I dont think the Sealey can be trusted? - try it again using resistance 2000ohms - not diode test.

Also retest The D854 make sure you get down to metal and there is not a coating of burnt flux.

[budm]

Re: Dell E173fpf - No led coming on

The MBR10100CT is not isolated tab, the metal tab is connected to the common Cathode which is the output side of the rectifier, the heat sink is connected to ground, so basically you short out the winding of the transformer with the Diodes! Please remove it. I should have asked if you replaced wit the same P/N.