olevia 437-s11 power supply shock question

[den3720]

Hi, I have been working on an olevia 37" LCD. The symptom of the tv is blue standbye light on, when you press the power button - nothing. I tried a dvd input no audio, no lcd panel activity with flashlight to indicated (bad inversion or ccfl). I assumed PS problem. I started with checking voltages to see if I am getting rectified dc after the bridge, if chopper trans has dc supply, and of course the output voltages on the secondary side. While I was checking i got a quick shock from touching a large heat-sink (bridge rec) on the primary side (largest sink visible in pic). I cut power discharged main filt cap and determined that the heatsink was directly soldered to ground on the primary side. I was thinking that voltage should not be present on ground - I think, I am no expert. In the mean time I have checked continuity the traces on the pri side. I have not discovered any trans or diodes or resistor that are shorted across ground. I was thinking that this symptom must be only occurring under load. My question concerns hot/cold ground. Is it possible that my ground lead on DVM was improperly connected. I simply connected to the - out of the bridge on the prim side. I know that one must place the black lead in different places when checking between prim and second voltages. Any information on this would be appreciated - Ted

[PlainBill]

Re: olevia 437-s11 power supply shock question

Hi, I have been working on an olevia 37" LCD. The symptom of the tv is blue standbye light on, when you press the power button - nothing. I tried a dvd input no audio, no lcd panel activity with flashlight to indicated (bad inversion or ccfl). I assumed PS problem. I started with checking voltages to see if I am getting rectified dc after the bridge, if chopper trans has dc supply, and of course the output voltages on the secondary side. While I was checking i got a quick shock from touching a large heat-sink (bridge rec) on the primary side (largest sink visible in pic). I cut power discharged main filt cap and determined that the heatsink was directly soldered to ground on the primary side. I was thinking that voltage should not be present on ground - I think, I am no expert. In the mean time I have checked continuity the traces on the pri side. I have not discovered any trans or diodes or resistor that are shorted across ground. I was thinking that this symptom must be only occurring under load. My question concerns hot/cold ground. Is it possible that my ground lead on DVM was improperly connected. I simply connected to the - out of the bridge on the prim side. I know that one must place the black lead in different places when checking between prim and second voltages. Any information on this would be appreciated - Ted

It's a good thing you have felines in your ancestry and have multiple lives. If you look at the back side of the power supply you will see a heavy white line running across the board. The portion to the left is the secondary side of the supply and it SHOULD be possible to work on that with impunity.

The primary side is more complex. While one side of the AC line is grounded, things get much more complicated when you include a bridge rectifier. In simple terms, the negative lead of the bridge and the negative terminal of the filter cap (and the heat sink in this case) vary in voltage as referenced to earth ground 60 times a second. The range on the - terminal is from 0 volts to -165 volts. The range on the + terminal is from 0 volts to +165 volts. It probably didn't escape your attention that this can pack a jolt!

PlainBill

[den3720]

Re: olevia 437-s11 power supply shock question

Thanks for the reply PlainBill. I assume this means that dc voltages at the + term of the filter cap should be around 165dc. Does that mean I need to place the black lead of the DVM on the negative of the filt cap to check dc volatages past the b. rectifier?

[PlainBill]

Re: olevia 437-s11 power supply shock question

Thanks for the reply PlainBill. I assume this means that dc voltages at the + term of the filter cap should be around 165dc. Does that mean I need to place the black lead of the DVM on the negative of the filt cap to check dc volatages past the b. rectifier?

You are correct, sir. You would also have a better chance of surviving the experience if you keep one hand in your pocket (or otherwise refrain from exposing your heart to 165 VDC).

PlainBill

[den3720]

Re: olevia 437-s11 power supply shock question

HI PlainBill, I tested the bridge rec for voltages. I first confirmed that on the AC-in + I got 120ac. I then switched DVM to DC and determined that on the out+ pin I got 165v dc. I thought I should get 320v dc is that correct? (I had the black lead on the out - pin.)

[PlainBill]

Re: olevia 437-s11 power supply shock question

HI PlainBill, I tested the bridge rec for voltages. I first confirmed that on the AC-in + I got 120ac. I then switched DVM to DC and determined that on the out+ pin I got 165v dc. I thought I should get 320v dc is that correct? (I had the black lead on the out - pin.)

165 volts is correct if the input voltage is 120VAC. The formula is VDC = (VAC x 1.41) - 1.5 volts.

PlainBill

[den3720]

Re: olevia 437-s11 power supply shock question

Thanks PlainBill, I am still checking voltages. I determined that All output voltages on secondary side are 0 with exception of 5vsb voltage. I determined that each of the transformers (3 on this board) have 165 on their primary and 0 on their secondary. I switch to AC measurement as well on the secondary side and found no activity. I read that sometimes you can monitor transformer activity with a DVM on AC. I am assuming that there is no chopping ocurring on the primary side to push-pull current thru the windings of the said trans. My supply has a PFC/PWC ic controller that performs both functions. The device is tda16858. I checked the main chopper FET. It has 165 on its drain and 0v on its gate, 0v on source. I also checked the 2 FETS k3683 found in the PFC section, one had 3v on the gate, 165 on drain and 5v on source, the other had 0 on gate, 3.2 on drain and ov on source. I think that I need to see if the PFC/PWC is getting proper input voltages. I have a question. If there is a fault condition in the chopper controller sensing circuit that causes the pfc/pwc controller to not start, is there any way to detect this condition before it shuts down?

[den3720]

Re: olevia 437-s11 power supply shock question

HI PlainBill, thanks for all the input. I just observered a strange occurence. While I was checking dc readings on the gate of a FET referenced earlier found in the PFC section the readings went like from 30vdc gradually down to 0vdc. Is that an indication of a bad cap?

[PlainBill]

Re: olevia 437-s11 power supply shock question

HI PlainBill, thanks for all the input. I just observered a strange occurence. While I was checking dc readings on the gate of a FET referenced earlier found in the PFC section the readings went like from 30vdc gradually down to 0vdc. Is that an indication of a bad cap?

That is an indication of either a bad solder joint, or a failure in the component driving the FET.

PlainBill

[den3720]

Re: olevia 437-s11 power supply shock question

Thanks PlainBill I appreciate it.

[ldk2bsure]

Re: olevia 437-s11 power supply shock question

I have the exact same problem with the same TV. Does anyone have the schematics to it. I also found this response from another post Thanks in advance

Larry
:

"I have a 24" Olevia LCD TV. Same symptoms (Stdby LED is on, press power and it flashes off, then back on). The USB cable to the Service Port also worked. But being of sound technical mind, I figured this means that the PC is supplying the +5v to the circuit. What I did was disassebled the TV, carefully disconnected all the cables, and opened it up to reveal the circuitry. I looked over the circuit and noticed the 1000uf/16v capacitor at position CS21 was failed and bulging. I removed the cap, tested it and verified that it was indeed failed. I went to a local Radio Shack and picked up a 1000uf/35v electrolytic, after all, the value is what mainly matters as long as it's not lower voltage than the original. I replaced the new CS21 capacitor back in the circuit (it is polarity sensitive, so pay attention to what the original mounting position is). I reassembled the TV and Viola! Works! No need for the USB cable to the Service Port!

I hope this helps someone!

-Matt "

[XmouseX]

Re: olevia 437-s11 power supply shock question

Ok, I am so glad to have found this forum. So here is the deal. I repair all kinds of electronics, but I am working on a Olevia 537H TV which stopped working during a lightning storm. I removed the power board and found a blown fuse and(this is the part I have not had to replace ever before) a blown out coil wound inductor. Due to the fact that it is ruined, I have no way of knowing the specs on it. I was wondering if anyone had any ideas? Thank you.

[leonardochen]

Re: olevia 437-s11 power supply shock question

Hi all
Where can I get the schematic for Olevia 437-s11 and how much ??
please advice?


Happy Holiday

[leonardochen]

Re: olevia 437-s11 power supply shock question

need value of c20 & c21 on PFC