Getting started with troubleshooting [Samsung 245BW]

[retiredcaps]

Re: Getting started with troubleshooting [Samsung 245BW]

Red transistor -
Black Pin 1, Red Pin 2 - 19.7 ohms
Black Pin 1, Red Pin 3 - 0.3 ohms
Black Pin 2, Red Pin 3 - 21.0 ohms

Green transistor -
Black Pin 1, Red Pin 2 - 19.7 ohms
Black Pin 1, Red Pin 3 - 0.3 ohms
Black Pin 2, Red Pin 3 - 21.0 ohms

Light blue transistor -
Black Pin 1, Red Pin 2 - 21.4 ohms
Black Pin 1, Red Pin 3 - 0.4 ohms
Black Pin 2, Red Pin 3 - 22.6 ohms

Magenta transistor -
(From the data sheet, it looks like pin 3 is the ground pin, so I used that for my black probe and measured the resistance between the other 4 pins)
Black Pin 3, Red Pin 1 - 19.5 ohms
Black Pin 3, Red Pin 2 - 21.4 ohms
Black Pin 3, Red Pin 4 - 700 ohms
Black Pin 3, Red Pin 5 - 590 ohms

Hmm, all the above readings would suggest that all those 4 components are possibly shorted.

Given how QM802 andQM803 were bad, it is possible that this board got some severe damage?

I would desolder just one transistor (say the red circled one) and retest it for a short. There could be something "in circuit" that gives these 4 transistors a "false" reading?

If you want to minimize the work involved in desoldering the red circled transistor, try to just "lift one leg" of the transistor and retest.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

1) What are the part numbers for each of the 4 colored transistors?

2) Test each of the above for shorts.

3) If there are no shorts, measure each pin for DC voltage with respect to ground. Use a ground screw for your black probe.

Red - EN210A 8222EN
Green - EN210A 8222EN
Couldn't find a datasheet for these 2

Light blue - N 8A FCQ10A04 S255K


Magenta - SIK (i think) 8008HFE


I tested them using the same method I used for the other MOSFETs, though I think the "light blue" transistor is a Schottky Barrier Diode, so I'm not sure if that's the proper way to test it.

Red transistor -
Black Pin 1, Red Pin 2 - 19.7 ohms
Black Pin 1, Red Pin 3 - 0.3 ohms
Black Pin 2, Red Pin 3 - 21.0 ohms

Green transistor -
Black Pin 1, Red Pin 2 - 19.7 ohms
Black Pin 1, Red Pin 3 - 0.3 ohms
Black Pin 2, Red Pin 3 - 21.0 ohms

Light blue transistor -
Black Pin 1, Red Pin 2 - 21.4 ohms
Black Pin 1, Red Pin 3 - 0.4 ohms
Black Pin 2, Red Pin 3 - 22.6 ohms

Magenta transistor -
(From the data sheet, it looks like pin 3 is the ground pin, so I used that for my black probe and measured the resistance between the other 4 pins)
Black Pin 3, Red Pin 1 - 19.5 ohms
Black Pin 3, Red Pin 2 - 21.4 ohms
Black Pin 3, Red Pin 4 - 700 ohms
Black Pin 3, Red Pin 5 - 590 ohms

[retiredcaps]

Re: Getting started with troubleshooting [Samsung 245BW]

Regarding the 384V DC and PFC, see PlainBill's post at

https://www.badcaps.net/forum/showpo...&postcount=171

the other Samsung245BW thread.

Some of the suggestions are now relevant to you now.

[retiredcaps]

Re: Getting started with troubleshooting [Samsung 245BW]

1) What are the part numbers for each of the 4 colored transistors?

2) Test each of the above for shorts.

3) If there are no shorts, measure each pin for DC voltage with respect to ground. Use a ground screw for your black probe.

[retiredcaps]

Re: Getting started with troubleshooting [Samsung 245BW]

I then checked the voltage across the main capacitor, that previously measured 160V. It now reads 384V!

Monitors bigger than 19 inch "normally" have 2 power supplies. 384V DC is "normal" when a PFC is involved. That is good news. The power supply is trying to start.

[retiredcaps]

Re: Getting started with troubleshooting [Samsung 245BW]

The measurements for the 1501-33 are:

Pin 1: 5.18V
Pin 2: 3.30V
Pin 3: 0V
Pin 4: 3.23V
Pin 5: 0V

The suffix in part numbers like the one above indicate the output voltage. So -33 denotes 3.3V DC. So pin 2, it spot on at 3.30V DC.

The part number on IC703 is "J412 953-18". I wasn't able to find a datasheet for this one. The measurements are:

Pin 1: 2.93V (3.18V if I turn the monitor off)
Pin 2: 0V
Pin 3: 1.78V (regardless of on or off)

-18 indicates 1.80V DC should be the output. Most of these parts should be with 1% of the output rating. That is 1.80 x 0.99 = 1.782. Let's say this voltage regulator is working properly because most multimeters are +/- 0.5% accuracy on DC V.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Ok, now this is weird. I searched other threads for "953-18" to see if anyone else had measurements I could compare against (which I did find, and I guess my readings are normal). I then checked the voltage across the main capacitor, that previously measured 160V. It now reads 384V!

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

If 5.0V standby is now steady, let's make sure it is reaching the logic board. The logic board tells the power supply to start.

See picture (one person in another thread questions why pictures are needed and implies that I'm an idiot for even asking).

List the part number and DC voltages each pin, of the red and yellow circled component (the two components that are designated IC on the PCB - one is IC703).

Measure each pin (except the big tab) with respect to ground. Use a ground screw on the logic board for ground.

The red circle is IC705, and the part number is AnaChip 1501-33. Here is the data sheet:
http://www.alldatasheet.com/datashee...IP/AP1501.html

The measurements for the 1501-33 are:

Pin 1: 5.18V
Pin 2: 3.30V
Pin 3: 0V
Pin 4: 3.23V
Pin 5: 0V

From what I can understand from the datasheet, it seems that Pins 1 through 4 have the correct values, but I'm not sure about Pin 5?

The part number on IC703 is "J412 953-18". I wasn't able to find a datasheet for this one. The measurements are:

Pin 1: 2.93V (3.18V if I turn the monitor off)
Pin 2: 0V
Pin 3: 1.78V (regardless of on or off)

The pins were counted from left to right using RetiredCaps' picture.

[retiredcaps]

Re: Getting started with troubleshooting [Samsung 245BW]

If 5.0V standby is now steady, let's make sure it is reaching the logic board. The logic board tells the power supply to start.

See picture (one person in another thread questions why pictures are needed and implies that I'm an idiot for even asking).

List the part number and DC voltages each pin, of the red and yellow circled component (the two components that are designated IC on the PCB - one is IC703).

Measure each pin (except the big tab) with respect to ground. Use a ground screw on the logic board for ground.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

You are probably narrowing down on the original issue, which caused the switching MOSFETs to fry in the first place. Do you get 24v with the inverter board disconnected? Keep the light bulb in circuit for the time being, it may save your bacon.

Even with the inverter board disconnected, I get 0V on the "24V" pins. I traced those pins back to the "+5.3V" pins on the connector on the left side of the board (using the continuity feature), and those +5.3V pins also measure 0V. I made sure the monitor was "on" and not in "standby" when measuring the voltages.

I don't know if it's relevant, but I also took measurements on the smaller cable on the left hand side, above the cable that has the S_B pin. They also measured 0V. The labels of those pins are, from top to bottom:

DET
ST/PWM_DIM
ANA_DIM
SOS
BL

[Th3_uN1Qu3]

Re: Getting started with troubleshooting [Samsung 245BW]

You are probably narrowing down on the original issue, which caused the switching MOSFETs to fry in the first place. Do you get 24v with the inverter board disconnected? Keep the light bulb in circuit for the time being, it may save your bacon.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Well, not fixed yet, but more progress...

I put in the new MOSFETs with a little silicone thermal paste (not the Arctic Silver, just to be safe) and put a new 1W 0.22 ohm resistor in RM801. I was also able to wire up that light bulb current limiter using an extension cord, so I was able to use that to make sure there wasn't a short somewhere else that would blow the resistor or the new MOSFETs.

I then connected the logic board to the power board, and now I get a steady 5.2V on the S_B pin, even with the logic board connected.

I connected the bezel buttons, and the power button lit up and turned on and off as I expected.

I then connected everything up (logic board to LVDS connector, power board to inverter board, invertor board to CCFL connectors, and attached a VGA cable from the monitor to my laptop. Turned on the monitor, and the display properties on my laptop picked up the monitor. I set it to extend my desktop to the 2nd display, and the monitor status light went from "standby" blinking to solid "on", but the screen didn't turn on. I then set the displays to go to sleep after 1 minute, and the monitor properly went from "on" to "standby", and also woke up properly when I moved the mouse.

I disconnected the logic board from the LVDS connector so I could flip over the chassis and access the pins on the logic and power board. I took measurements on the power board connector that runs to the inverter board (the ones marked "+24V", and they all read 0V.

I'm guessing that means there's still something wrong on my power board, right? At least the SMPS issue is fixed

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Thanks Th3_uN1Qu3, I found some links for how to build a "light bulb current limiter" which, from the descriptions, sounds exactly like what you described. I think this one may be the easiest for me to wire up myself:

http://www.io.com/~beckerdo/guitars/...ter/index.html

[Th3_uN1Qu3]

Re: Getting started with troubleshooting [Samsung 245BW]

To do the test with the light bulb as you mentioned, I'm guessing I'd need to get a light bulb socket like the one I attached, and some alligator clips to clip to the metal prongs holding the fuse?

Yes, something like that. You connect the bulb in place of the fuse on the AC line. Circuit wise, it's the first thing on the board after the power socket. Though i usually just hack an extension cord and plug the device into that, leaving the fuse in place - splice one wire of the cord, wire the bulb socket, wrap it in a little electrical tape, et voila you have an universal power supply short tester.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

The ones you bought are a tad weaker. The difference is low enough to be ignored though - in extreme cases it could have appeared as a manufacturing tolerance. Drop 'em in and see what gives.

To make sure you don't blow those too if there's something else wrong, replace the fuse with a 60 or 100W light bulb. It has to be the regular incandescent type, a CFL won't work. The bulb should flash briefly as the main capacitor is charged, then it should light at very low brightness when you power up the monitor. If it glows brightly, immediately disconnect the monitor from the mains and look for other sources of trouble.

Ah ok, thanks for clarifying!

To do the test with the light bulb as you mentioned, I'm guessing I'd need to get a light bulb socket like the one I attached, and some alligator clips to clip to the metal prongs holding the fuse? Also, which fuse would I connect it to since there are 2 fuses?

[Th3_uN1Qu3]

Re: Getting started with troubleshooting [Samsung 245BW]

The ones you bought are a tad weaker. The difference is low enough to be ignored though - in extreme cases it could have appeared as a manufacturing tolerance. Drop 'em in and see what gives.

To make sure you don't blow those too if there's something else wrong, replace the fuse with a 60 or 100W light bulb. It has to be the regular incandescent type, a CFL won't work. The bulb should flash briefly as the main capacitor is charged, then it should light at very low brightness when you power up the monitor. If it glows brightly, immediately disconnect the monitor from the mains and look for other sources of trouble.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

My new MOSFETs arrived today, but I had a quick question. On closer inspection, I see that the MOSFETs I purchased are FQPF 9N50CF, but the original broken ones are FQPF 9N50C.

Mouser.com shows the 9N50C as obsolete, so I guess I don't really have a choice, and the datasheets for the two are almost identical. However, there are a few differences, so I'm not sure if I should be concerned:

FQPF9N50CF.pdf

FQPF9N50C.pdf

[Rtech]

Re: Getting started with troubleshooting [Samsung 245BW]

Unlikely,Mosfets do fail,and regularly take out this resistor.On a Dell with a one board system and usually designated by the letters FPf, 6-8 components can fail,and calls for a rebuild of the Power supply,so you are not doing so bad.Good luck with the repair, and let us know how you get on.

[nerdbot]

Re: Getting started with troubleshooting [Samsung 245BW]

Thanks Rtech, I may actually try and put one of those together just for fun.

While I'm waiting for the parts to arrive, I was wondering - should I be looking for what caused the MOSFETs to short out? I ordered twice as many mosfets as I needed, but if there's anything I can be doing now to minimize problems when they get here, I'd like to do that.

[Rtech]

Re: Getting started with troubleshooting [Samsung 245BW]

Glad you now know why the resistor, burnt out.This liitle Mosfet tester, is easily made from scrap components,and if I am in any doubt at all whether I have one that is good or not..then this quickly sorts it out:-

http://translate.google.com/translat...dor_mosfet.htm