Flat line on Panasonic TX-29AD2DP

[bbjunkie]

Just happened to mention to a guy at work that I was messing around with some TVs in my spare time and he offered me free for collection a big and rather heavy Panasonic TX-29AD2DP (a really nice 29" CRT in 4:3 format)

He told me that it had developed a fault (a horizontal very bright line across the screen with no other picture.. I think it's called field collapse?) and that instead of getting it fixed he went out and bought a big 1080p plasma.

Got it home, still in the car though!

Won't be looking at this for a while, as I already have 4 in the "junk pile"

Anyone come across this before? After some searching it has been suggested checking for dry joints on the scan coils & field output chip. So, i'll start with that and go from there. I've downloaded the service manual so will have some interesting bedtime reading


Jim

[berniedd]

Re: Flat line on Panasonic TX-29AD2DP

The vertical scanning has failed. Suspect the vertical output IC or transistor. Also change the big electrolytic capacitors in and around that circuit. While it is possible, the vertical scanning yoke may also be suspect, but a failed yoke is not commonly seen. Also be aware that running the set, even briefly, with only a single horizontal line on the crt can permanently burn the phosphors on the screen. Turn down the brightness control to minimum if you have to test your repair, and don't run the set longer than you have to while in such a state.

[rayrod81]

Re: Flat line on Panasonic TX-29AD2DP

It was a common problem in Panasonic tube sets. Most of the time it was cold solder joint in the vertical deflection circuit or a bad vertical IC. The cap in the vertical deflection circuit may need to be replaced also. Very cheap and easy fix. Don't poke around too much with the TV turned on because there are high voltages in the horizontal section that can be pretty dangerous.

[bbjunkie]

Re: Flat line on Panasonic TX-29AD2DP

Ok, got the set into the workshop and the main board out (eventually) located I561 a TDA8175 which I touched up with fresh solder. I removed C563, a 470uF 35v electrolytic and C561, a 2200uF 35v electrolytic. Measuring ESR the 470uF measured 0.06 and the 2200uf measured 0.00 ohms

I see there's a chinese supplier selling the TDA8175 for $4.00 while the only source here in the UK I can find is cricklewood and they are asking £18.00

Does anyone have any cheaper reliable sources for these now rare IC's ?

Depending on what you guys think of the 0.06 ohm ESR I may put it back together and test, if I have to order caps then im grounded until after Christmas as my only source tomorrow is Maplin who afaik dont stock low esr caps.

Suggestions welcomed

Attached for reference is the schematic for the section in question

Jim

[Th3_uN1Qu3]

Re: Flat line on Panasonic TX-29AD2DP

Test the 2200uF cap with the ohms range on your multimeter - it could be shorted. If it doesn't registered as shorted put the caps back in and try the set again - the ESR on the 470uF cap looks normal.

[popeye]

Re: Flat line on Panasonic TX-29AD2DP

Ok, got the set into the workshop and the main board out (eventually) located I561 a TDA8175 which I touched up with fresh solder. I removed C563, a 470uF 35v electrolytic and C561, a 2200uF 35v electrolytic. Measuring ESR the 470uF measured 0.06 and the 2200uf measured 0.00 ohms

I see there's a chinese supplier selling the TDA8175 for $4.00 while the only source here in the UK I can find is cricklewood and they are asking £18.00

Does anyone have any cheaper reliable sources for these now rare IC's ?

Depending on what you guys think of the 0.06 ohm ESR I may put it back together and test, if I have to order caps then im grounded until after Christmas as my only source tomorrow is Maplin who afaik dont stock low esr caps.



Suggestions welcomed

Attached for reference is the schematic for the section in question

Jim

Change both caps check the 27 volt line if the ic has gone replace it then you are good to go simples.

[bbjunkie]

Re: Flat line on Panasonic TX-29AD2DP

Test the 2200uF cap with the ohms range on your multimeter - it could be shorted. If it doesn't registered as shorted put the caps back in and try the set again - the ESR on the 470uF cap looks normal.

Started higher dropped to about 15.4M ohms and kept falling slowly

I'm away for Christmas so won't be looking at it again until Boxing day.

[Th3_uN1Qu3]

Re: Flat line on Panasonic TX-29AD2DP

Definitely not shorted then.

[bbjunkie]

Re: Flat line on Panasonic TX-29AD2DP

Got the caps re-fitted this afternoon, retouched the field output IC solder connections and I now have a picture. Won't hold my breath though.. the picture was flickering occasionally. Once I get the following sorted, I will leave it on for a few hours to see what happens.

Turns out there is very little sound from it - can barely hear something in the centre speaker and nothing from the left and right.

Suggestions welcome

Jim