Tech Chat Old engineer seeking help with Panasonic LED TV

Sounds like a backlight fault, but I guess you already suspect that. @michael-dranfield is the man you need, he too is a TV engineer of old, but has kept himself up to date on TVs and still fixes this sort of junk modern flat TV.

As I've used the mention feature of this forum (his @name) Michael will have received an e-mail notification about this post and thread. No doubt when time permits, he will shed some light on the problem (pun intended).

Shock horror, I found the full service manual for this TV, I've just soiled our Data Library with a copy of it for you and others download. 😉 

Apparently, it uses the LH69 Chassis.

p.s.

Curiosity got the better of me and I had a look at the circuit, I'm now suffering extreme trauma.... will have to go look at a good old BRC-3000 service manual to restore sanity.

TX-32LZD81 is quite old now and lit by CCFL backlighting, in other words fluorescent tubes, as the tubes loose emission they do darken and there is no cure apart from fitting new ones, eventually the emission will fall so low the set won't come on and it will blink an error code for backlighting failure. 

Thank you Michael  & Crusty. I suppose the next question has to be is it fixable at a sensible cost?  And where would one buy tubes, number not specified?

Reading this thread is giving me flashbacks to my old studio and replacing the tubes in our touchscreens.

You can probably do a search online for "panasonic 32 inch tv ccfl backlight tubes" or similar and see where that takes you.

I would point out though that TV sets of that size frequently turn up in household auctions for nominal sums. A few weeks ago I bought a Panasonic 43" UHD "smart" TV in immaculate condition for £75 including premium and VAT. You might wish to just upgrade to a LED-backlight set and save yourself the aggravation.

@boater-sam I very much doubt you will be able to buy brand new ones now, these went out of fashion over 10 years ago, your only hope will be a donor set with the same tubes, the same LCD panel will be fitted to many different sets so you could try an Internet search using the part number of the back of the LCD panel.

Have to agree with the above, this is unlikely to be an economical repair, the TV dates from around 2008 so already 16-years old. I found a complete working set on eBay for £89, pricey considering the age and what you can get nowadays. Also found a UK site with spare parts for this TV but no, unfortunately no backlights. Perhaps time to call it quits and buy something newer.

p.s.

One for Michael, would it be possible to modify the circuit to use LED backlights?

LED backlight inverters are relatively simple things, normally just a boost converter with current feedback. I design them for those long narrow LCD displays that are used as route maps in trains.

It's usually not too hard to pull LCD modules apart. Worth a try. What do you have to lose? At least you'd know if it's likely to be practical to fit LED strings in place of the CCFL tubes.

Getting suitable LED strings isn't too hard either.

I'd also suggest calling it a day. A few years ago I was asked to look at an 'old' Sharp LCD with backlight problems. It was for a friend of my daughter otherwise I wouldn't even have bothered. Usual story....single mother, low income so I said I'd see what I could do. There was an inverter fault which was nothing more than a duff transistor. Fixed but then uneven lighting...and sometimes it wouldn't come on (with an error code). I managed to get a couple of replacement backlight tubes (a pig to fit) but it got the set going at minimal cost for a couple of years. Then other tubes failed and this time nothing available. CFL is old technology and hasn't been used for many years. 32" LCD's are cheap by todays standards and can be bought new in most supermarkets. Cheaper to do that than waste time trying to revive the old Panasonic (although it goes against our ethos to chuck things out). It's easier to fix a 70's colour TV than one of these things!!

Fore warned is fore armed, thanks guys.

I will run it until it expires then it will go to the tip.

@crustytv while it would in theory be possible to convert to led backlighting it wouldn't be that easy, for a start you would have to get it optically perfect to ensure even light distribution to avoid any dark patches or shading on the screen but two bigger problems would have to be overcome CCFL tubes need a high striking voltage, typically 1kv to start, where as just a couple of led strips would need a constant current power source at 80 volts or so, then you would have to find a way of disabling the Panasonic inverter and over riding the error detection circuit which will kick in and switch the set off it it sees the inverter is not functioning. There are other sets which would convert a lot easier than a Panasonic due to not having such a comprehensive protection circuits.