Hisense 55P6 - No power no standby

[samsonn]

Hi all,

I've got a Hisense 55P6 which won't turn on and has no standby light.

I've cracked it open and measured the voltages on the connector between the PSU and main board, but got 0V on all pins. I have 330V on both of the big capacitors so we're getting power.

Not sure where to check next. Grateful for any help.

PSU details: Hisense RSAG7.820.7748 HLL-4360WQ. (I found a replacement but it's a bit pricey http://www.mxmee.com.au/index.php?ro...oduct_id=11815)

[chrismurphy]

Re: Hisense 55P6 - No power no standby

resolder all connections on the two transformers with the yellow tape

[samsonn]

Re: Hisense 55P6 - No power no standby

Thanks Chris I gave that a go but no luck.

[R_J]

Re: Hisense 55P6 - No power no standby

Check that D816~D819 are not shorted, If they are ok, it is likely a problem in the primary circuit around N803, when checking voltages on this ic you must use hot ground (IE:C811 negative lead). Check pin8 (or W823) It should be close to main cap voltage, then check pin3, this is the VCC, post the voltage reading
Be careful checking voltages in the primary side, you are dealing with Mains voltage

[chrismurphy]

Re: Hisense 55P6 - No power no standby

check fast recovery diodes vd816 to vd818 for shorts
these boards usually have these fail

[chrismurphy]

Re: Hisense 55P6 - No power no standby

sorry for the repeat post R_J posted the same

[samsonn]

Re: Hisense 55P6 - No power no standby

All the diodes seem fine. The voltages around the IC are:
Pin 3: 20v
Pin 8: 180v

[samsonn]

Re: Hisense 55P6 - No power no standby

From reading some other posts a Vcc of 20v seems reasonable? Not sure where would be best to check next, probably to verify that the IC is still good but not sure how to do that.

[R_J]

Re: Hisense 55P6 - No power no standby

VCC of 20v is normal, so the ic should at least be in burst mode, which would give some voltage on the secondary, It could be that the ic is bad and not driving the mosfets.

[samsonn]

Re: Hisense 55P6 - No power no standby

So if I were to measure the voltage on the gate of v805 and v806 that would give some indication on wether the ic is working?

[samsonn]

Re: Hisense 55P6 - No power no standby

Looks like the source and drain of v805 are shorted so guess I'll replace that and see if it works.

[R_J]

Re: Hisense 55P6 - No power no standby

Check the resistors and diode in the gate drive of that mosfet, hopefully they are ok and it is only a bad fet.

[samsonn]

Re: Hisense 55P6 - No power no standby

So I've been thinking about the replacement mosfet I ordered. The dead mosfet had "CS840F A9h" written on it, which I could find the datasheet for but nobody was selling them. I ended up ordering this: https://au.rs-online.com/web/p/mosfe...escriptionLink as it seemed to be a pretty close match at the time.

I've since found that an IRFS840 would be an exact(?) match for the broken FET, and there are a few for sale on ebay (bit expensive tho). Wondering if its worth ordering the better match or if I should stick with plan A and uses the FETs I've already ordered?