Hpt5054 no power no clicking

[tvprobs]

Hello,

So I've recently inherited a 50" samsung plasma that was working up until a move. It had issues with powering off at random times and is now completely dead. The inrush current thermistor was blown and cracked when i opened it up and I've been trouble shooting for a little over a week to no solution. I'm pretty novice, but i have an electrical engineering background from school, but changed up because i liked the hobby more than the schooling. I'm handy with tools like multi-meter and soldering iron. However, i seem to lack the expertise needed to crack this one.

I'm getting a stby of 5.1V and a PS-On of 4.3V. If it wasn't for the blown thermistor i would have assumed an issue with the Main bored first. I've gone through and re-flowed solder to a few joints. Got some replacement parts in. Switch was melted and changed out the thermistor. I have the Vs and Va kit, but so far everything i've pulled (transistor/mosfet) wise have tested well.

I'm only getting 1.8V on my 5.3V, 18V, and 12V points. I'm thinking it must be a Va or Vs issue because I'm getting good voltage through the AC/DC (163VDC) portion and up to the transistor that powers the switches to the bridge rectifier.

Short of just replacing every resistor, transistor, and MOSFET that's in the kit, or testing 1 by 1 every component out of circuit i'm at a loss. Tell me what you may need from me and i'll send the info your way.

Thanks in advance!

[R_J]

Re: Hpt5054 no power no clicking

If the thermistor (NT801s) is blown its likely the relay is bad, The relay contacts short across the thermistor when the tv is turned on, when the relay contacts go bad, all the curent passes through the thermistor causing it to open
What switch was melted?
Post pictures of the board or at least the bn44 number

[tvprobs]

Re: Hpt5054 no power no clicking

BN44-00162A (PSPF531801A) switch RL801S was melted and i've replaced that one. I have another on hand to replace RL802S, but i've seen no reason to replace it so far. I've plugged it back in and cannot get it to even click the relays. I'm getting <1V hitting them which isn't enough to bring them on. I've followed the schematic and found QQ803 is getting 20VDC through the Emmiter and Base. I'll post pictures tomorrow, but the schematic is attached.

[tvprobs]

Re: Hpt5054 no power no clicking

Here are the pics for the board with the switch and thermistor replaced. I did have to scrape away some of the board to get the thermistor re-attached, but otherwise it appears in decent shape.

[dick_barton]

Re: Hpt5054 no power no clicking

So what voltage does ICQ805 has on the input / output pins?

[tvprobs]

Re: Hpt5054 no power no clicking

ICQ805 is showing .01V at input. .03V at output. -.23V at GRND.

QQ803 showing 20.2Ve. 20.3Vb. and -.03Vc.

CQ807 showing .13V at positive terminal.

Strange finding. I've been working mostly with the board off the TV. However, i decided to do some other fact checking. When i plug the main board in, all of my Va, Vs, Standby, PS_ON, 5.3V, 18V, 12V, points all fluctuate between .3V and -.3V

However, when it's not plugged in everything is stable to the voltages mentioned in the first post.

[dick_barton]

Re: Hpt5054 no power no clicking

With the mainboard disconnected do you have the standby voltage ?
If ICQ805 has no voltage In/Out (15V regulator) then the relays cannot be energised.

[tvprobs]

Re: Hpt5054 no power no clicking

I have the standby voltage of 5.2V when not connected. Also have PS_ON of 4.3V.

That's where i'm starting to be at a loss. I really need to try to narrow this down before i just start pulling parts 1 by one at semi-random.

I feel like i should have my 5.3V with or without the board plugged in and am curious if i need to work back from there. I just don't know enough about how the voltage changes throughout the TV once the main board is hooked up and the TV tries to kick on. I'm sure there may be 1 part or multiple part failures when a thermistor blows, but i cannot seem to track down any visual clues with and without a multimeter.

[dick_barton]

Re: Hpt5054 no power no clicking

With the mainboard disconnected from the power supply if you short PS_On to Ground (0 Volts) do the relays click on even if only momentary.

[tvprobs]

Re: Hpt5054 no power no clicking

when shorted nothing happens at the relays. So still not voltage going to the rectifiers. Va, and Vs test points drop to negative voltage. Va=-2.8V(spikes to -4.1V then falls to steady voltage) and Vs= -4.1V.

[R_J]

Re: Hpt5054 no power no clicking

Using hot ground. Check the voltage on QQ803 (E), (C) and (B). QQ803 supplies voltage to the ICQ805 regulator (in) and the 15 volts output goes to the relay RL802s so QQ803 Emitter is likely around 20 volts
Using cold ground measure the voltage on QQ851 (C). when power supply is OFF this voltage will be low, when power supply is ON this voltage should go high 3 to 4 volts. this will light the opto coupler PCQ802 causing the photo transistor part to go low.
QQ810 should be turned on via RQ837 providing the ground for the opto PCQ802 emitter so when the optos photo transistor is on RQ819 goes low (to hot ground) turning on QQ803

[tvprobs]

Re: Hpt5054 no power no clicking

Using hot ground. Check the voltage on QQ803 (E), (C) and (B). QQ803 supplies voltage to the ICQ805 regulator (in) and the 15 volts output goes to the relay RL802s so QQ803 Emitter is likely around 20 volts
Using cold ground measure the voltage on QQ851 (C). when power supply is OFF this voltage will be low, when power supply is ON this voltage should go high 3 to 4 volts. this will light the opto coupler PCQ802 causing the photo transistor part to go low.
QQ810 should be turned on via RQ837 providing the ground for the opto PCQ802 emitter so when the optos photo transistor is on RQ819 goes low (to hot ground) turning on QQ803

OK. here's what i've found so far.

OFF STATE:
QQ803 E: 20.2V C: -0.03V B: 20.3V

QQ851 E: 0V C: 0.09V B: 1.8V

QQ810 E: -0.05V C: 0.18V B: 0.18V

Resistors match the output

ON STATE (PS_ON goes to ground 0V):

QQ851 E: 0V C:1.4V B: 0V

Opto-coupler getting +.9V on anode 0V on cathode

QQ810 E: 0.7V C:0.2V B:0.2V

QQ803 E:19V C: 12-13V B: 19V *****These voltages are bouncing.

ICQ then puts out a voltage bouncing between 10.9V and 11.5V which goes to Vcc.

Relay 801 is only getting 0.2V and relay 802 is getting voltage bouncing around 11V. Diodes seem good on these too.

If i put my lead on +side of relay 802 it will actually click on then off when i was testing. I'm thinking maybe a bad capacitor somewhere is causing this voltage to bounce around? i followed my bouncing voltage and it seems to be coming from the PFC side. VAC standby input is steady.

[tvprobs]

Re: Hpt5054 no power no clicking

So update on the TV front. After working back through the board after the testing above and pulling some components just to be sure they were good. I found that on top of 1 cap being low. There were blown joints on the second relay. TV has been up and running for over an hour and seems great. Thank you all for the help. It definitely pointed my in the right direction to finally solve this case. I had been working on it for a while.

[R_J]

Re: Hpt5054 no power no clicking

Good to here its working.