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

[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.

[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

[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

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

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

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

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

[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

[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

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?

[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

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

[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

[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

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

If you're lucky, it will be cold/cracked joints on either QS801/802 or QX801/802 worst case you'll be replacing mosfets, resistors and diodes

PS if you don't have easy access to 1SS184 diodes, I should soon have plenty of them

[retiredcaps]

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

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

Canada and Australia are almost in the same boat when it comes to buying stuff online. I wait up to 60 days for my stuff to arrive, but I get it at very good prices. I try to anticipate my needs well in advance.

[psmedley]

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

I hedged my bets on the 1S184 diodes - I found some in Thailand with expedited shipping today - Only $US6.50 so I should soon have a plethora (well 60) of them.

[TheTVCoop]

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

Any news on this repair?

[psmedley]

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

Any news on this repair?

Not until parts I have ordered arrive

[psmedley]

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

I hadn't mentioned it before, but there were 3 25v 680uf caps that were swelled/leaking on the X & Y main boards - replaced them today in anticipation that my diodes/resistors can't be too far away. They were well and truly knackered - ESR meters reports < 100uf and > 6 ohms. Oh and they were Samwha's