TNPA5349 Buffer replacement

[flocko]

I have a Panasonic TX-P42S30B that has shorted SN board TNPA5349 fitted. And was hoping for the normally shorted Q401/Q402/ect fault But after lifting all the legs on all the components It still testing S/c on SN2,testing shows short between C+E on Q661 and short all three legs on Q662 the rest test good? so started to check Buffer ICs and found IC 4803 showing shorts all over . so here`s my problem, I am looking for some one to replace this IC for me. My eyes are not what they were I can supply the IC just need it fitted so if there is anyone in the UK that could help an old man out with this please message me Thanks Flocko

[tw2005]

Re: TNPA5349 Buffer replacement

Does sympathy count as help? You have my sympathy

[flocko]

Re: TNPA5349 Buffer replacement

Thanks TW yes that goes a long way, well I have a chip on the way from sparedparts.com £10 and I have my digital microscope, I have changed 20-30 gamma chips and all the SMD bits on these SN/SC/SS boards with no problems so I will give it a go, as long as I can get the old one off clean, I am going to change the shorted Q661 and Q662 , and with the buffer chip removed run the board in the set, I think it should power up with the one buffer chip missing ?. I have news on that other 37"Panasonic set with the TNPA5063 SC board in that is all fixed and working, I will post details on here when I have more time on my hands. soon be the start of the F1 year, I don't think I can make it over to you for the first race, but my money will still be on Mr Button to do it again this year. Flocko

[tom66]

Re: TNPA5349 Buffer replacement

A short on the SN power connector would not be caused by a bad buffer IC. It is still possible the IC is bad, but there are also probably other faults you need to check for first.

[tw2005]

Re: TNPA5349 Buffer replacement

Thanks TW yes that goes a long way, well I have a chip on the way from sparedparts.com £10 and I have my digital microscope, I have changed 20-30 gamma chips and all the SMD bits on these SN/SC/SS boards with no problems so I will give it a go, as long as I can get the old one off clean, I am going to change the shorted Q661 and Q662 , and with the buffer chip removed run the board in the set, I think it should power up with the one buffer chip missing ?. I have news on that other 37"Panasonic set with the TNPA5063 SC board in that is all fixed and working, I will post details on here when I have more time on my hands. soon be the start of the F1 year, I don't think I can make it over to you for the first race, but my money will still be on Mr Button to do it again this year. Flocko

I'll have to check out the dates. So button is still racing, all the talk was he had no ride. i have to back our young gun, can't wait to see him perform in competitive car. lets hope not another single team whitewash.

With those panasonic buffers, those Ics have that grey sealant which also has heatsinking properties under the chip and it sticks very,very well. i tried and failed on a bad board, I think the trick is to completely remove every trace of it from the pins, maybe carefully cut the legs hard against the ic.
desolder the pins, then grip and twist that ic free.

but I failed so better advice may be out there on this. not sure how many have tried yet on a panasonic board
do you think replacing those fets ar it or maybe the usual smd stuff like drivers and transistors as well?

[flocko]

Re: TNPA5349 Buffer replacement

Hi Tom if you read through you will see that Q661+Q662 are shorted but that is all apart from the buffer IC, I had lifted the legs on all 17 devices on the board and SN2 was still showing short, that lead me to the buffer IC4803 short, my Question to TW was did he think the set would power on with one missing buffer and Q661/662 replaced? Flocko

[tom66]

Re: TNPA5349 Buffer replacement

You still wouldn't get short on SN2 if buffer ICs were bad... something else is shorted. The ICs can't short to ground, only to their own floating ground, which would only cause Vscan/-Vad to drop out (causing a 7 blink SOS)

The set may work with a missing IC but any other ICs that chain data off of it will be blank. So if it's the top most or bottom most IC it might not work. If it's in the middle it might work.

[tw2005]

Re: TNPA5349 Buffer replacement

Hi Tom if you read through you will see that Q661+Q662 are shorted but that is all apart from the buffer IC, I had lifted the legs on all 17 devices on the board and SN2 was still showing short, that lead me to the buffer IC4803 short, my Question to TW was did he think the set would power on with one missing buffer and Q661/662 replaced? Flocko

no idea, never tried,

[flocko]

Re: TNPA5349 Buffer replacement

the IC is showing shorts to ground that is how I found it , if I run my meter in continuity over the tab sockets and board ground this one rings out and after removing the silicon from it most pins are short to ground? all other tabs are clear

[tom66]

Re: TNPA5349 Buffer replacement

You would need to test to floating ground. Can you get a photo of the SN board?

Due to the internal parasitic diode structures, shorts to actual (cold-earth) ground aren't necessarily bad...

If they are bad, it indicates something else on the SN side is still short, besides the IC.

The ICs themselves have -no- direct electrical connection to ground, they are floating -190V (-Vad) below ground and the outputs can switch between -Vad and up to -Vad + Vscan in normal operation.

So that in itself, indicates that -Vad or Vscan is shorted somewhere to ground (not the buffer IC)

[flocko]

Re: TNPA5349 Buffer replacement

with all legs lifted on diodes + IGBT from board the SN2 shows 13.9 ohms across the socket, I only get buzz from meter when set to continuity? shows nothing in diode or 200ohms mode between tab and ground and only on this buffer IC. but have had this before ,the last time when the buffer was removed so was the short

[tom66]

Re: TNPA5349 Buffer replacement

So you've isolated every transistor and still getting 13 ohms?

Try isolating the big white 2.2ohm 5W resistor, from memory that's the Vscan source for the buffer ICs, would eliminate a potential short from there.

I've never seen this before, really odd, perhaps a small little diode is shorted somewhere.

[flocko]

Re: TNPA5349 Buffer replacement

Tom GTV sell the chip on eBay and in there add they say top buffer is the normal one to go (heat)and goes s/c, and tested should read 800ohm one way and o/s the other ? bad buffer will read s/c.i can only think they mean to read across the diodes by the side of the IC? if you look I have cut and re joined the resistor not that on my meter reads 2.37 ohm

[tw2005]

Re: TNPA5349 Buffer replacement

are you sure all the legs are free and not a solder dag still touching the board?

[tom66]

Re: TNPA5349 Buffer replacement

I have heard that the buffer ICs can go on this set; I've documented a possible cause elsewhere on this forum, but I can't see how when you isolate all the parts you have, you still get a short across SN. You have essentially removed the only path to the buffer ICs by disconnecting all those transistors so something else must still be wrong, somewhere... I don't know where...

[flocko]

Re: TNPA5349 Buffer replacement

I have now started to go round checking on the pads were the legs have been lifted on the diodes + IGBTs to see if any show shorted there was a small Fet Q600 that I had missed but there is no short on that. I will also pull the 2 cap from across SN2 socket as well do you think that I am right about the test across the diodes by the buffers as these show short?

[flocko]

Re: TNPA5349 Buffer replacement

After checking the pads no shorts found, But now think the anodes on D461/462 (RFN20) are the floating ground for the buffers as if you diode test from here to tab connectors you get IC 4803 showing short in diode mode and 200ohm ? only way to see if this the short at SN2 is to take buffer from board will get on to that tomorrow afternoon.

[tom66]

Re: TNPA5349 Buffer replacement

tw, do you have a schematic of this board?

[flocko]

Re: TNPA5349 Buffer replacement

Tom just had a look and Alastair repaired one a little time ago. but he has not been on here for a while,

[Neelix]

Re: TNPA5349 Buffer replacement

Saw service manual for same SN board, but circuit diagram is poor quality and can't make out a thing