50" Samsung Plasma (model number PS50Q91HD) - possible purchase

[tom66]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Someon's just contacted me about their Samsung PS42C7HD clicking - I might take a chance on it if it's just cold joints.

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

If it helps, I *think* this is the schematic for your PSU.

The correct schematic is at

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Tried to reply on Saturday but server upgrades got in the way

All transistor readings were higher than 30 ohms, so I'll assume the sub boards are OK.

I do plan on replacing the accompanying resistors as well as the diodes and mosfets before I try powering up again. ie all the parts described in http://www.ebay.com.au/itm/160644626388

I just need to wait for all the parts to arrive now - Adelaide electronics stores suck

[retiredcaps]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

I just do a simple all pins combination to see if they are shorted. For a 3 pin transistor, measure the resistance between pins 1-2, 1-3, and 2-3. Any reading under 30 ohms warrants desoldering and verifying out of circuit.

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

I didn't get a chance to actually turn the TV before it shorted. I plugged in the AC, it wasn't clicking, so I made a quick pit stop, came back and it was clicking

Any tips on testing the Q's?
Is:
<quote>
POSITIVE PROBE TO: -----NEGATIVE PROBE TO: -----RESISTANCE READING-- CONCLUSION:
Emitter------- -- Base---------- Less than 150 ohm ------Transistor is NPN
Base --------------Emitter --------Infinity ----------------Transistor is NPN

POSITIVE PROBE TO: NEGATIVE PROBE TO: RESISTANCE READING: CONCLUSION:
-Emitter------------Base ---------Infinity ---------------- Transistor is PNP
Base --------------- Emitter --- - Less than 150 ohm ------- Transistor is PNP

Some defective indications of transistors: Resistance between any pair of the terminals is less than 10 ohms* means that the transistor is shorted. Resistance between base and emitter or base collector for both the forward and reverse application of ohmmeter probes is infinity (meter needle don't deflect)* means that the transistor is open. Transistors overheats (except power transistors) during normal operating condition means that the transistor is shorted.
</quote>

Sufficient?

[tom66]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Q's and D's can be tested; R's will need to be pulled.

Did TV show any picture before it shorted again?

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

OK ordered the SMD diodes retiredcaps suggested.

Whilst I wait for them to arrive, I've been reading http://preher-tv.blogspot.com.au/201...-repaired.html on the other common issues on similar Samsung power supplies.

This mentions components like:
RX802, RX803, RX832 and RX833 are open or have a seriously increased resistance.
RX804 and RX805 are open or have a seriously increased resistance.

These all measure around 50 Ohms in circuit vs the stated values of:
RX802, RX803, RX832 and RX833= 20 ohm
RX804 and RX805= 10k ohm

Is this due to them being measured in circuit??

It also mentions problems on the sub boards:
QS803, QS804, QS805 and QS806 one or more shorted(check for open junctions as well)
DS823 shorted(may be open as well) check between pin 1 and 3
RS859 may be open or have a seriously increased resistance

Can these parts be tested in circuit?
QS803 and QS804= NPN 20V 2A SMD BJT(marking ZG)
QS805 and QS806= PNP 20V 2A SMD BJT(marking ZH)
D823= 18V 0.35W SMD zener diode(marking 8Y)
RS859= 4.7 ohm SMD resistor

Cheers,

Paul

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

My only hesitation is the shipping time from the us to australia

[retiredcaps]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

They have a list of 'similar' products - any recommendations?

Need 48 spare? 50 for $6.00 + free shipping

http://www.ebay.com/itm/160586650557

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

http://preher-tv.blogspot.com.au/201...-clicking.html suggests "DS801 and DS802 are both 1SS184T5LFT, UFR dual package common cathode SMD diodes" I find these on mouser at:
http://au.mouser.com/ProductDetail/T...sljcLw5w%3d%3d

However RS in Australia has this as a discontinued product:
http://australia.rs-online.com/web/p/rectifier/3174558/

They have a list of 'similar' products - any recommendations?

[retiredcaps]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Numbered left to right - 1 to 3 - pin 2 is on a side by itself

The diodes are definitely bad "in circuit". You can remove them and verify out of circuit. You will have to remove them anyway if they are bad.

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Numbered left to right - 1 to 3 - pin 2 is on a side by itself

[retiredcaps]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Next question will be any tips on replacing SMD diodes???

CuriousInventor makes an excellent series of soldering videos.

http://www.youtube.com/watch?v=3NN7UGWYmBY

[retiredcaps]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

How are you numbering the pins? If pin 2 is the only pin on one side, those diodes are definitely shorted. That means pin 1 and 3 are on the same side. If yes, both diodes are shorted.

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

DS801: (first pin red, 2nd black)
Pin 1-2 = 0.006v
Pin 2-1 = 0.006v
Pin 2-3 = 0.006v
Pin 3-2 = 0.006v

DS802: (first pin red, 2nd black)
Pin 1-2 = 0.006v
Pin 2-1 = 0.006v
Pin 2-3 = 0.006v
Pin 3-2 = 0.006v

So given in diode mode the reverse reading should be open loop I'll say these are bad?

Next question will be any tips on replacing SMD diodes???

[retiredcaps]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

can anyone explain how to test DS801/DS802? it has three pins - not sure how to identify which pin is what.

I get ~10Ohms across the pins and reversing the red/black gives the same value - so I'm assuming they're shorted? as being a diode they should be open circuit the other way around?

If the diode looks like this -><-, treat it like 2 separate diodes when testing. That is, pin -> is one diode and <- is the other.

Put your multimeter in diode test mode. Measure pin 1-2, then reverse the probes. Measure pin 2-3 and then reverse the probes. You should have 4 readings in total.

In diode test mode, the unit of measure is volts, not ohms. So instead of 10 ohms, you have 0.10V (10 mV). That would be a shorted diode.

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Reading http://preher-tv.blogspot.com.au/201...-clicking.html - can anyone explain how to test DS801/DS802? it has three pins - not sure how to identify which pin is what.

I get ~10Ohms across the pins and reversing the red/black gives the same value - so I'm assuming they're shorted? as being a diode they should be open circuit the other way around?

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

uggh mosfets finally arrived from RS today.

Installed them, plugged in tv - yippee - only one click from psu. Went for a quick pit stop, came back and the fuse had blown and the new mosfets are shorted Turns out I'd forgotten to tighten the screws securing the mosfets to the heatsink - however I wouldn't have thought being in standby for a couple of minutes could be enough to blow them???

[tom66]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

If it helps, I *think* this is the schematic for your PSU.

[psmedley]

Re: 50" Samsung Plasma (model number PS50Q91HD) - possible purchase

Well given the packaging - farnell don't have a suitable replacement... So... it was either ebay from China, the US or the UK, or RS with the parts on backorder.... (and maybe from the UK)

Just wish Jaycar sold mosfets so I could get something today :P