Hannspree HSG1143 repair, no power, blown IC905

[Chungalin]

This 42" LCD TV had no power, possibly due to a surge. Power supply is labeled as 715G3858-P01-W30-003U.

5A main fuse open, but the main problem here is that IC905 (DIP-8 PWM regulator) has violently blown and the top layer has disappeared, making impossible to identify it. Sometimes I find the pieces inside the cover and I’m able to reconstruct its "face", but no luck this time.

I google a bit and I find I’m not the only one. Finally there’re two sources stating this is a Power Integrations TNY277PN (or TNY277PG, it’s functionally the same). Also recommend to check zener ZD907 (Philips BZX79-C9V1). No problems with other diodes. I just detect that one of the 3 main 450V filter caps has subtly leaked through one leg (none bulged). I replace it.

Since I don’t have any TNY277, I try with a TNY275. This is the Standby regulator, so it’s expected that 15W should be enough. I try it briefly and it works. Then I order the right IC, just for peace of mind.

[jellytot]

Re: Hannspree HSG1143 repair, no power, blown IC905

Hi Chungalin. I've got exactly the same fault condition on a Hsg1142 set with the same PS. must be a weakness with these supplies resulting in catastrophic failure with chopper ic905. mine is also decapitated with zd907 partially shorted or leaky.

[Chungalin]

Re: Hannspree HSG1143 repair, no power, blown IC905

Thanks for reporting your case. Sometimes the aim of creating this threads is to detect "trending" failures in some models.

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

Hey guys sorry to drag this one up. I've just had this issue with my hannspree, I've replaced all the components mentioned and the TV is working again! Thanks!!

However it's now making a high pitched whistle from the power board, any ideas what might be causing that? I don't even know where to start.
Thanks

[Chungalin]

Re: Hannspree HSG1143 repair, no power, blown IC905

Try replacing the electrolytic cap that is very close to IC905. High frequency noise from PSU usually means bad caps in primary side. Have you replaced all 3x68uF/450V main filter caps?

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

Thanks I'll order those.
I've done some checking with the ohmmeter, one of the little smd caps right beside the ic905, it's resistance is not dropping to 0. The seemingly identical one beside it does tend towards 0. Could this be an issue? How can I tell what smd to replace it with. The board says c948

[Chungalin]

Re: Hannspree HSG1143 repair, no power, blown IC905

Capacitors cannot be checked with ohmmeter, unless they’re shorted, which is something rather unlikely. Check other threads about ESR. Anyway, if you have doubts, just replace them. I wouldn’t care about SMD caps at this moment, before you have ruled out electrolytic ones.

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

Thanks for all the help mate!

I've ordered a heap of different ones to try. Also got a cheap cap tester. Hopefully I can sort it now.

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

I've taken out and tested all the electrolytic type caps, they all check out ok with the tester. Is there anything else to look at? I think the sound seems to be coming from one of the transformers.

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

The whistling is coming from this thing, 738174-183N etc etc.
See the photo.

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

Update, TV working perfect now.

I put it all back together was just about to go buy a new one and said I'll leave it on while I was cleaning up all my testing gear. It was on for about 5 mins with the bad whistle, then there was a pop and the whistle stopped. TV 100% now

[dskall]

Re: Hannspree HSG1143 repair, no power, blown IC905

Not sure if that pop was a good thing, but whatever works

[budm]

Re: Hannspree HSG1143 repair, no power, blown IC905

That is the inductor for the PFC, I wonder if the PFC boosted Voltage is still present after the 'POP'.

[Chungalin]

Re: Hannspree HSG1143 repair, no power, blown IC905

Never heard any POP that "fixed" something.

[ptrain]

Re: Hannspree HSG1143 repair, no power, blown IC905

A month on now and the TV is still fine.

[Branko Sudic]

Re: Hannspree HSG1143 repair, no power, blown IC905

After replacement IC905 and ZD907 i had the same problem wisting sound. I found that D991 ( 2A05 ) leaky! I put MUR460 and sound disaperad.

[Fesmitronica]

Re: Hannspree HSG1143 repair, no power, blown IC905

Hello
This is my first post and need help.
Have the same problem with the IC905 BLOW , switch to TNY280PN because the TNY277PN is out of stock and the ZD907 with a leak and i have 3.6V with a lot of noise.
Already saw resistors , capacitors , pc817 , kia431 and everything is ok but te standby voltage are to low.
Someone can help me with some ideas??