Samsung PS50a410

[nickdablack]

Hi all. Trying to put to use my electronics diploma (which has sat idle for 10 years). Thought I would try my hand at fixing some plasma's.

To get to the point I have picked up a Samsung PS50A410C1D. On 1st inspection the main fuse on the power supply is blown and the 2 larger capacitors on the board are clearly fried.

I plan to replace the fuse and capacitors and see how I go. Any recommendations to a TV repair novice?

[retiredcaps]

A blown main fuse warrants checking your bridge rectifier and power mosfets for shorts.

[nickdablack]

Update: On the bottom of the board found a bit of burning on some surface mount components. I'll add that to the other items to check and replace.

[tom66]

It is normal for the capacitors with a plastic disc on them to have the disc pop up after time. If you remove the disc to reveal the vent, does the capacitor still appear bulged?

See attached.

The blue circled device is the bridge rectifier. Mentally number the pins 1 to 4. Check continuity between each pin. In general, no reading should show under 0.5V except across the two outer pins, if a device further down the line is shorted.

The red circled devices are power MOSFETs probably (although one or two may be the PFC diodes.) If they have three legs, check between each and every pin both ways for shorts (<0.2V on diode test.) If it is a two legged device, just check both ways (>0.5V on diode test.)

I see there are several fuses on the board. Which one of these blew?

[gsmy]

Hi can I ask a few questions regarding the component testing you outlined? I am going over my proscan ps (another post) checking components and have a question regarding the bridge rectifer. I checked it per your method and it shows open between pin 2 and 3. Is that correct? The other measurements are 1 to 2 .516v, 1 to 3 .514v, 1 to 4 .495v 2 to 4 .508v, 3 to 4 .505v. The numbers on the rectifer are D155B60 935.

Next I have two 3 pin components like the red circled ones. If I measure across the two outer pins I get a short. From an outer pin to the center pin I get .528v and .521v. The numbers on these are AUK 802 STK1625.

Even though the picture in my proscan post is not mine, it is a good shot of the board. Still working on getting pics of mine posted.

[nickdablack]

Originally Posted by tom66

It is normal for the capacitors with a plastic disc on them to have the disc pop up after time. If you remove the disc to reveal the vent, does the capacitor still appear bulged?


I see there are several fuses on the board. Which one of these blew?

Thanks Tom. That should help me substantially. The caps are definitely gone. There is visible burning on the side of at least one of them.
I am still hunting down a circuit diagram so I can identify what the components were that burned.

The only fuse that went was next to ac input. (circled in green) Other fuses show continuity.

Thanks again for your help. I will let you know how i go.

[nickdablack]

Originally Posted by tom66

The blue circled device is the bridge rectifier. Mentally number the pins 1 to 4. Check continuity between each pin. In general, no reading should show under 0.5V except across the two outer pins, if a device further down the line is shorted.

Pins 1 to 4 measure 0.032V as predicted. All other measurements are greater than 0.5V

[tom66]

Originally Posted by nickdablack

Pins 1 to 4 measure 0.032V as predicted. All other measurements are greater than 0.5V

That's hopeful, the bridge rectifier is often one of the cheapest and easiest parts on TVs to repair. Given the size of the heatsink, it dissipates a lot of heat and is very much the first line for surges from the mains. You will need a replacement bridge rectifier and some new thermal compound.

You should remove the device and re-test it to verify it's not the rest of the circuit at fault. Unscrew it from the heatsink, then use solder wick or a solder sucker.

[nickdablack]

Found a circuit diagram. http://dc307.4shared.com/doc/owK8ThvU/preview.html
RP858 - 10(2012)F
RP816 - 22(2012)F
DP807 - 1SS355
RP823 - 10K(2012)F

Filling in the gaps.

[tom66]

Good job on finding the proprietary schematics .

The burning on the caps, is it potentially from a nearby component blowing up? (not uncommon with power electronics!)

[nickdablack]

Originally Posted by nickdablack

Found a circuit diagram. http://dc307.4shared.com/doc/owK8ThvU/preview.html
RP858 - 10(2012)F
RP816 - 22(2012)F
Filling in the gaps.

ok need to work out what value RP858 and RP816 are.

[tom66]

A MOSFET is more tricky, because some other components are often damaged when it goes short circuit (usually the gate resistors). However, you do have a schematic, which is very useful when repairing these, so it shouldn't be too difficult... Can you post a picture of the damage? I suspect the PWM/PFC IC will also have been damaged by this.

[nickdablack]

Originally Posted by tom66

The red circled devices are power MOSFETs probably (although one or two may be the PFC diodes.) If they have three legs, check between each and every pin both ways for shorts (<0.2V on diode test.) If it is a two legged device, just check both ways (>0.5V on diode test.)

All have 3 legs.
DS401 0.002V across 1 & 3. 0.444 across 2 & 1, 2 & 3
DS402 0.002V across 1 & 3. 0.441 across 2 & 1, 2 & 3
DA401 0.002V across 1 & 3. 0.242 across 2 & 1, 2 & 3
DA402 0.002V across 1 & 3. 0.241 across 2 & 1, 2 & 3
QA401 1.536V across 1 & 3. 0.545 across 2 & 3
DM401 0.002V across 1 & 3. 0.351 across 2 & 1, 2 & 3
DM404 0.002V across 1 & 3. 0.351 across 2 & 1, 2 & 3


Sorry typing these all down as I for for my own reference.

[nickdablack]

DP802 0.002V across 1 & 3. 0.423 across 2 & 1, 2 & 3
QP801 (Next to damaged capacitor) 0.032V between 2 & 3 all other combinations open.
QP802 1.1V between Pins 1&2 and 1&3 0.03V between 2 & 3

QS802 0.53v between 2&1 and 2&3. 0.016 between 1 & 3
Qs801 0.53v between 2&1 and 2&3. 0.016 between 1 & 3
ICM801 (has 6 pins) no idea what to mesure
ICB802 0.57b between 1 & 3 0.38 between pins 2 and 3 0.575v between 1 & 2

[nickdablack]

On closer inspection qp801 looks damaged. I'll remove it and do some measurements.

[nickdablack]

Found the culprit. Had to remove the burnt looking capacitor to get to it. Short on pins 2 to 3. Pin 1 is open. It also linked directly to the surface mount resistors that are looking burnt.

And you were right Tom. The burnt capacitor looks like it might be fine.

Wont be able to buy components until monday. Will have to wait until then.

[nickdablack]

I posted a photo of the burned resistors in my 2nd post. It shows damage to rp858 and rp816. Let me know if a better picture will help.

[tom66]

I couldn't find a 19N60 in stock at digikey, but I found an equivalent part.

MOSFET: http://search.digikey.com/us/en/prod...63-5-ND/654637 (20N60, handles higher current)

Measure the resistors in inches. They may be 0.12" x 0.06" in which case they are 1206 SMD resistors. What is the resistance of them indicated in the schematic?

[nickdablack]

Originally Posted by tom66

I couldn't find a 19N60 in stock at digikey, but I found an equivalent part.

MOSFET: http://search.digikey.com/us/en/prod...63-5-ND/654637 (20N60, handles higher current)

Measure the resistors in inches. They may be 0.12" x 0.06" in which case they are 1206 SMD resistors. What is the resistance of them indicated in the schematic?

Found the 19N60 from a local supplier. The info on the schematic labeled the SMD's as:
RP858 - 10(2012)F
RP816 - 22(2012)F
I've been trying to google those figures, but no luck so far. I'll have to invest in some calipers to measure them.

Maybe this? http://parts.digikey.com/1/parts/776...12t-1r0-f.html

[tom66]

Originally Posted by nickdablack

Found the 19N60 from a local supplier. The info on the schematic labeled the SMD's as:
RP858 - 10(2012)F
RP816 - 22(2012)F
I've been trying to google those figures, but no luck so far. I'll have to invest in some calipers to measure them.

Maybe this? http://parts.digikey.com/1/parts/776...12t-1r0-f.html

10 ohm and 22 ohm 1206 (2012 metric) resistors. I use a cheap £7 digital caliper from eBay to measure them. Resistors are very cheap though (~15 cents for 20), there's no harm in ordering some other sizes to be sure.

Samsung uses metric measurements on their schematics. I'm not sure why, it's a sensible idea in theory, but the rest of the world still uses imperial for most electronics.