TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

[tom66]

Odd failure here.. TH-42PZ85B with a 2 blink code indicating low or short Vsus. When SC was removed, code changed to 7. Tested SC and found it has no direct short but 120 ohms between Vsus and GND.

Loads of IGBTs dead but the odd thing is, the Vsus isn't dead short, so I'm lost as to how this has happened - suspect the short is hiding behind some component, but not sure what exactly.

Anyone else seen this? Will just order a new board at £15

[tw2005]

Re: TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

120ohms would be good enough to be classified as dead short on Vsus. Normally resistance there on the 2010 boards is 300K - 3meg.

I know every now and then a board is not dead short at SC2 for the 5081 boards, and throws a 10 blink instead of 4.

[tom66]

Re: TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

Yep agreed it's short just weird it's not dead short. It looks like the SUS UP path died, has about 0.1 ohm C-E then the VAD pass FET popped about 100 ohm drain-source. SUS-DN looks like it survived, kinda odd. Not too worried, will use this as a spare parts board. The board is pretty cheap as it rarely fails on the PZ80s. This has to be my first one after something like 12 P board and 1 A board fault.

[tw2005]

Re: TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

Yep agreed it's short just weird it's not dead short. It looks like the SUS UP path died, has about 0.1 ohm C-E then the VAD pass FET popped about 100 ohm drain-source. SUS-DN looks like it survived, kinda odd. Not too worried, will use this as a spare parts board. The board is pretty cheap as it rarely fails on the PZ80s. This has to be my first one after something like 12 P board and 1 A board fault.

I think if the MC201/301 module issue did not exist, these would have to be the pick for reliability so long as power consumption was not a consideration.

I double read the post just to convince myself I was reading SC failure, pretty rare.

[tom66]

Re: TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

I think most Panny plasmas are pretty reliable all considered, they just have consistent issues (such as the loose screw issue.) On the modern panels (2011 onwards) they actually look pretty easy to repair, you'd only have to replace IGBTs & gate drivers... maybe a buffer IC in the worst case...

Certainly, considering some of what Samsung & LG were putting out at the time, Panny plasmas are excellent.

[keeney123]

Re: TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

Odd failure here.. TH-42PZ85B with a 2 blink code indicating low or short Vsus. When SC was removed, code changed to 7. Tested SC and found it has no direct short but 120 ohms between Vsus and GND.

Loads of IGBTs dead but the odd thing is, the Vsus isn't dead short, so I'm lost as to how this has happened - suspect the short is hiding behind some component, but not sure what exactly.

Anyone else seen this? Will just order a new board at £15

I have seen high ohm shorts on new production board caused by dust on the image used to made the board. If one did not properly get rid of short then I have seen them grow back together. We use to use a large capacitor and charge it up and then apply it to board. The problem with that is they can grow back together. We found using a Fluke meter in the Ohm scale one could hold one probe stationary and move the other probe to find the lowest resistance. Once we found the lowest resistance we moved the stationary probe over to this area to find a more specific lower reading. We could narrow down to a few inches and then use a X-acto knife to cut between the runs and then use lacquer fingernail polish to coat the cut. Of course with multi-layer boards I guess one would throw it away.

[tom66]

Re: TNPA4657 failure (TH-42PZ85B) w/ 120 ohms between VSUS and GND

Can confirm SC board fixed the fault.