Toshiba 52XV645U LCD Dead Power Supply

[RCFLYER]

I have a Toshiba REGZA 52XV645U LCD TV with a dead power supply
(V28A000962A1) With the help of a link on this website I found the culprit. https://www.badcaps.net/forum/showthread.php?t=15787 The fusible resistor R850 is open. My question is I found 2 resistors R827 and R828 showing thermal heat damage. What can cause these resistors to get so hot?
I'm replacing two 150uf 450v capacitors that looked a little rounded but measured ok.

[Namenotfound]

Re: Toshiba 52XV645U LCD Dead Power Supply

I have a similar problem. A resistor reading open. I have yet to check those two. I just started "tv repairs" so I don't know very much however iv been reading a book on power supplies. But aside from the resistor I "found" (I was looking for a schematic and found a "repair kit" on eBay that pointed me in the right direction my meter reads 30vac from the chassis ground to neutral. Is this normal? Also I get ac readings past the bridge rectifier 50vac or so. Is that because of the way the meter works? I'm sorry please bare with my ignorance. And sorry for posting on your thread but I had to make my first post somewhere. Any help is appreciated.

[Namenotfound]

Re: Toshiba 52XV645U LCD Dead Power Supply

Rcflyer what should those read. I'm getting .2oms. is that correct?

Sorry I found it. First time Iv seen milli ohms.

[budm]

Re: Toshiba 52XV645U LCD Dead Power Supply

27m Ohms = 0.027 ohms, it is OK you are basically reading your probes resistance. The one on the right is 1.8 Ohms. The section of your pictures with heated reistors are in the PFC Voltage booster section.
BTW, those AC voltage reading are due to there is no safety Ground wire connected to the chassis, as long as you are getting 120VAC at the AC input connector, it is OK. You use chassis as the ground ref point when you measure the voltage in the secondary side, the primary side circuit ground ref point is the negative leg of the main filter caps (those 450VDC cap).
The fusible resistor that blown open probably due to shorted out MOSFETs for the PFC circuit.

[Ltank]

Re: Toshiba 52XV645U LCD Dead Power Supply

I have had another set where a shorted part caused the low ohm 2 watt resistor to open. I was curious why use such a low resistance that will heat up and open. In over 30 years as an industrial electronics tech I dont remember coming across this before.

[budm]

Re: Toshiba 52XV645U LCD Dead Power Supply

It is not just regular resistor, it is fusible type.
Learn more here:

[Namenotfound]

Re: Toshiba 52XV645U LCD Dead Power Supply

Thank you! I bought one of those cheap esr/everything meters, it's not in yet. Any opinions on those? I'll check those MOSFETs tomorrow.

[budm]

Re: Toshiba 52XV645U LCD Dead Power Supply

You can use your meter in Ohm mode to check for shorts between the combination of all 3 legs of the MOSFET. When semiconductor is shorted out, there is no need to use Diode mode for testing them, I use Ohm mode so I can also see if there is leakage resistance of the semiconductor junction.

[Namenotfound]

Re: Toshiba 52XV645U LCD Dead Power Supply

So I tested 5 MOSFETs and one pnp. The pic below is of my results. I was under the impression that I should have read OL when discharged with the diode check. However when switched to ohms readings were in M ohms. Is this usual or am I doing it wrong? Prob just a lack in experience. Also if I need to be posting somewhere else let me know where.

[Namenotfound]

Re: Toshiba 52XV645U LCD Dead Power Supply

The readings on the MOSFETs are between drain and source. All other resistance readings were OL. So I think the second one (q821) is bad or going bad? Resistance is higher? I checked it several times.

[Namenotfound]

Re: Toshiba 52XV645U LCD Dead Power Supply

I posted that wrong it's the first one q860a