Samsung PS-42Q7HD clicking, blue flashing LED, no power

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Okay I think i've made some progress.. With PSON and VSON... I checked the voltage outputs, ALL are present except the Vs. I decided to measure the voltage on all the electrolytic caps along that Vs line of the PSU.. 395V across the large filter caps, 0v on the cap beside sub board 1, and obviously 0v on the secondary caps... Checked the voltage on Sub Board 1's Vcc pin and it was 0V, (sub board 2 is working and has 3.2V on it's Vcc)....

So I followed the path of Sub Board 1's Vcc supply, which was jumped across the board back to a PNP transistor QU803 (KMPS 751Y 603) near the standby section.. Before the base resistor and emitter of QU803 there is a cap with 13.6v across it.. This also feeds sub board 2 so I know it's good.. Essentially, there is voltage on one side of QU803 and none on the other... Took it out of circuit and the junctions test 0.505v and 0.660v...

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Okay after about an hour searching I found this on Farnell's, a replacement MPS741. I'm gonna buy one, put it in .... (stand way back from it :-) ) Then try power it on again and see if I can get the Vs to work..

http://ie.farnell.com/diodes-inc/ztx...ditmatch=rel_3

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Put in the new PNP transistor for QU803 and still no go... The same 13.7 volts is at the collector and base of the transistor, with nothing at the emitter.. Both sides of the base resistor (which is fine) are also at 13.7 volts as well...

I'm gonna try to test the supply voltage to sub board 1 when I turn on the PSU and see if it is shutting down because of a short... And pull the sub board off the main board for testing.... this one is difficult

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Having established that there was no voltage reaching Sub Board 1, I soldered my DMM probes to the GND and Vcc of Sub Board 1 to see if there was any initial voltage on power on... Plugged in and the voltage started to rise in a negative direction before shutting down..

So I pulled off Sub Board 1, and none of the components tested bad... Fortunately, I had the identical Sub Board 2 (which I know to be good since Va is good) to compare the main IC (Resonant mode PWM control) ... turns out that the IC on Sub Board 1 is shorted from the Vcc to Drive Output B..

Gonna order the chip from that site and take it to the next stage..

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Just spent three hours trying to get that 16 pin IC out of the sub board, and replacing with the new one... My soldering iron really sucks.. Sloppy job putting it in as well tbh...

Put the power supply back connected to the power, plugged in, relay comes on.... Tested for Vs and there was nothing...

HUGE BANG when I shorted somewhere I shouldnt..

Started putting the TV back together, and started thinking about the "call of shame". Hooked the other boards back to the PSU and somehow it came on!!! It seems that the Vs doesnt not come up, even with the VS-on jumped to ground, unless the other boards are connected.. Not sure how long it's gonna stay up for, but at least it proves that it is just the PSU.

So in total: One fuse, Two Power Mosfets, Ten Capacitors, One Resonant Mode PWM Controller, One Transistor (that didnt need to be replaced)...

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

I think I may have spoken too soon. turned the screen over and the TV is coming on alright, but it's periodically pulsing... Havent seen this symptom in my plasma TV book.

http://www.youtube.com/watch?v=VOwogbnk4X0

[tom66]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Vset or Vs is probably unstable.

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

See the reason I was fixing this was to try and get the PSU up temporarily, just to make sure that it hadnt blown any of the other boards... (i.e. rather than buy a new PSU only to find the Y Sus board was also blown). Once this was confirmed, I was gonna buy a new PSU, to give it the best chance of a long lasting repair..

I suppose if I can confirm that the pulsing is caused by and unstable voltage on the PSU, this is the most confirmation that I can get..

[tom66]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Vset is generated by the sub PSU board, I think...

[craig417]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

I have one of these sets that clicks and blinking light. If i unplug y board power cable no clicking or light flashing. Take it my y board is at fault?.

[tom66]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Yes, and/or buffer boards.

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Looking at this one again..

To refresh I have the PSU back up and running, but it's acting like this..

http://www.youtube.com/watch?v=VOwogbnk4X0

I've checked the Vs voltage and like tom said, the voltage is varying between 156V and 180V ... Vs is meant to be 198V for this model... It seems more like a "structured" cycling of the power as if some OV or OC protection is shutting it down.



Just as a check there, I pulled the connection to the large sub power board LJ44-00105A. (This board takes a feed from the Main PSU and passes it on to the Ysus and Zsus boards).. When I pull the cable to this sub power board, the Vs voltage stays at 198.8 on the main PSU... So it seems that there is a fault further down the chain..

On the positive side I have the main PSU fully working.

[ben7]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Looking at this one again..

To refresh I have the PSU back up and running, but it's acting like this..

http://www.youtube.com/watch?v=VOwogbnk4X0

I've checked the Vs voltage and like tom said, the voltage is varying between 156V and 180V ... Vs is meant to be 198V for this model... It seems more like a "structured" cycling of the power as if some OV or OC protection is shutting it down.



Just as a check there, I pulled the connection to the large sub power board LJ44-00105A. (This board takes a feed from the Main PSU and passes it on to the Ysus and Zsus boards).. When I pull the cable to this sub power board, the Vs voltage stays at 198.8 on the main PSU... So it seems that there is a fault further down the chain..

On the positive side I have the main PSU fully working.

Replace all the capacitors on that thing. Small capacitors tend to make the circuits behave like this when they go bad!

[tom66]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Check Vset too. If Vset is unstable, it can cause too much current to be drawn from Vs, causing your fault.

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

I've tested with boards in and out to see what happens..

PSU with sub board connected - 198.8v stable
PSU with sub board and Ysus connected - 198.8 stable
PSU with sub board and Zsus connected - 198.8 stable.
PSU with sub board, Ysus and Zsus connected - voltage varies from 156-180v

I'm thinking that there is a component, which could realistically be on any of the boards, that is failing under load. Gonna be very difficult to isolate this problem, as the failure only occurs with all boards connected...

Found a cap on the Sub board that is 350V 4.7uF, coming up on my ESR meter as 4.6.uF and ESR of 12.6ohms.. I'll replace that first and move on...

[tom66]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

That would be a good idea.

Alternative proposal: Plasma panel gas does not discharge properly if it is not primed first. If it is primed too much it will discharge too easily leading to very bright light output and lots of power from PSU causing it to shut down. If it is primed too little it will not work properly (dark image and maldischarge typically.)

If one of the priming voltages, Vset, Vscan etc are incorrect, or the Yrr/Yfr are wrong, you will see a drop in Vs. (Plasma panel sustaining draws almost all power on Vs; it's the main power rail.)

And, the panel will not sustain properly if the X-main (common electrode driver) is disconnected, and it will not sustain at all if the Y-main (scan electrode driver) is disconnected.

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Swapped out that cap on the sub board.. Still the same..

Took these measurements while the screen is pulsing:



I need to find some way to isolate the PSU first and put a load on it.. If I put four 25V bulbs in series and use a resistor to limit the current, I could use this as a dummy load for Vs? Does this sound safe/crazy?

[tom66]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Ve is bad then. Not seen that before, haven't considered what that might do... hmm.

Anyway, for a Vs load, why not use a 230V lightbulb? 100W should be fine for ~85W load on Vs.

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power

Ve is bad then. Not seen that before, haven't considered what that might do... hmm.

Sorry tom.. I edited it wrongly in photoshop.. TWICE!!!!
I'll change it again now..

[JonathanAnon]

Re: Samsung PS-42Q7HD clicking, blue flashing LED, no power



Okay above are the correct figures that I pulled when the screen was on but pulsating..

Just as a test I swopped the sub boards (both DYP-42V5).. changing the 16 pin IC brought the Vs voltage back up, but I was never happy with the solder job I did...



When I swopped the boards the TV starts clicking and doesnt come on at all.. So it seems that there IS a problem still with that sub board that I soldered, but this problem is only evident under load.. I've tested all components on both sub boards and they match. Dont seem to be able to buy that sub board separately... May just bite the bullet and order the PSU..