Technika LCD19DVDID dead

[tom66]

Re: Technika LCD19DVDID dead

Gate resistor - if that's the one you have marked as R? then it's 26 ohms, the diode to it's 11 o'clock checks fine in circuit (drop of approx 0.53 volts)

I'm baffled then. What does the Vcc charging resistor measure as?

[bbjunkie]

Re: Technika LCD19DVDID dead

which one is that?

[tom66]

Re: Technika LCD19DVDID dead

which one is that?

Connects from HV to Vcc cap.

Also check the Vcc and main winding are both nearly s/c. If it's not, then the transformer has failed.

[bbjunkie]

Re: Technika LCD19DVDID dead

Connects from HV to Vcc cap.

In your diagram, is that the one to the right of startup cap?

Excuse my stupidity

[tom66]

Re: Technika LCD19DVDID dead

In your diagram, is that the one to the right of startup cap?

Excuse my stupidity

Yep.

If it's too high of a value the controller won't startup properly.

As you've got an unstable Vcc, something is not charging up that capacitor once the supply starts up.

[bbjunkie]

Re: Technika LCD19DVDID dead

Resistor is 1.55m ohms and in spec

Transformer measuring 1.2 ohms

[bbjunkie]

Re: Technika LCD19DVDID dead

When I measure from -ve on main cap to charge resistor end nearest diodes I get 0vdc 0.05vac and when I measure the other side of resistor i get 333 - 336 vdc

[tom66]

Re: Technika LCD19DVDID dead

When I measure from -ve on main cap to charge resistor end nearest diodes I get 0vdc 0.05vac and when I measure the other side of resistor i get 333 - 336 vdc

Sounds right. I have no idea what to suggest next; everything *seems* in order, there are no component failures, but it's still not working. There's the vague possibility the controller is dead, but you'd need a scope to double check.

[bbjunkie]

Re: Technika LCD19DVDID dead

The learning curve just got steeper!

Ok, well im ordering that isolating transformer on Tuesday so it'll have to wait til then.
Hopefully i've another telly coming tomorrow to keep me busy :-) (with intermittent shutdown)

Anyway, thanks for your time, I really appreciate it. It's been a real learning experience.

[tom66]

Re: Technika LCD19DVDID dead

Hopefully i've another telly coming tomorrow to keep me busy :-) (with intermittent shutdown)

Intermittent shutdown. If it's a Vestel, I wish you good luck: they are nasty supplies. I had one with the very same fault. I've tried to repair 3 17PW22/17PW15 series supplies so far; every attempt has ended in me buying a new one (luckily I've now found a cheap source for them.)

Anyway, thanks for your time, I really appreciate it. It's been a real learning experience.

I'm glad to help. It's nice to pass on experience. Almost all of these tests I've asked you to do have been passed on from other members of this forum and others. I don't have a formal education in any of this stuff.

[bbjunkie]

Re: Technika LCD19DVDID dead

It's a JVC LT-32A61SJ

Will start a thread when it arrives

Hopefully it wont be too bad, because I can't find any service docs for it!

Actually it's not intermittent shutdown.. just checked again.. it's intermittent stuck in standby.

[tom66]

Re: Technika LCD19DVDID dead

Okay, you look to be clear. JVC are a good manufacturer of TVs and they make most of their own stuff, they don't import Vestel crap. Intermittently stuck in standby sounds like bad caps but JVC use good caps, just look at this power supply...

http://www.lcdtvparts.co.uk/images/P1100905.JPG

Full of Rubycons.

And... Service manual:

Btw, where you find it? I've been looking for nice JVC/Sony sets to repair. They are beautifully engineered. Panasonic too; I repaired a Panasonic Viera Plasma (42") - top notch quality and awesomely overengineered. The Y-sustain had 40 something MOSFETs on it and the bulk capacitance on the Vs rail was more than 5,000uF(!!) spread across several boards. Of course full of Rubycon, Chemicon and Nichicon (quality) but only a few Panasonic caps, strange! Because of such a large capacitance, there was even a HV present indicator, which stayed lit when the caps were charged to more than about 40V.

[bbjunkie]

Re: Technika LCD19DVDID dead

The Y-sustain had 40 something MOSFETs on it and the bulk capacitance on the Vs rail was more than 5,000uF(!!) spread across several boards. Of course full of Rubycon, Chemicon and Nichicon (quality) but only a few Panasonic caps, strange! Because of such a large capacitance, there was even a HV present indicator, which stayed lit when the caps were charged to more than about 40V.

nice!!

Picked it up off eBay - probably paid a little more than it was worth as it has no stand or remote (where do all these remotes go!) but should get my money back and some beer money to boot.

[tom66]

Re: Technika LCD19DVDID dead

nice!!

Very nice. In the end, a single shorted MOSFET brought it down. It cost me £50 which was pretty cheap for a 42" full HD set. Owner thought it was a power supply problem but 5 mins with the flowchart and I had isolated the Y-sus as being faulty, then noticed people on eBay were selling the FETs for these boards, quickly isolated it (there were 6 in parallel) and it worked, to my surprise! I added another one in before I sold it.

Picked it up off eBay - probably paid a little more than it was worth as it has no stand or remote (where do all these remotes go!) but should get my money back and some beer money to boot.

I sell no-name 32" LCD TVs for £100 or so, and a brand name one would go for around £130-£150, depending on condition. I wouldn't pay any more than £35 for a 32" name brand, because you take a big risk on there being more than the initial fault.

[bbjunkie]

Re: Technika LCD19DVDID dead

Did ok then, got it for £34. Made him an offer of £30 and we met at £34 (plus shipping of 12 quid)

[tom66]

Re: Technika LCD19DVDID dead

Did ok then, got it for £34. Made him an offer of £30 and we met at £34 (plus shipping of 12 quid)

Nice. Most TVs I see on eBay go for a lot more. Like about £100. I need to look more carefully for buy it now / make offer listings.

[bbjunkie]

Re: Technika LCD19DVDID dead

no you dont they are hard enough to find

[bbjunkie]

Re: Technika LCD19DVDID dead

Hello again

When I measure from -ve on main cap to charge resistor end nearest diodes I get 0vdc 0.05vac and when I measure the other side of resistor i get 333 - 336 vdc

I have spent the morning tracing the circuit and drawing a circuit diagram to see if it will help me understand the circuit better.

What i've drawn has confused me a bit, I couldn't understand why measuring between the hot end of the charge resistor R24 (which is between HV and Vin on PWM controller) and -ve on the main cap is giving me 0vdc but yet measuring the other side was giving me 333-336 volts dc

Turns out the legend on the pcb wasn't actually indicating the - leg of the cap.. there is another legend identical below the other leg. I had been making the measurement with respect to HV instead of hot ground.

Now i've got the black lead on the correct pin of the cap, i'm seeing 333 volts DC rock solid on the HV side of R24. On the other side of R24, in circuit im seeing a very jumpy voltage varying from about 12vdc to 18vdc or so (impossible to measure the exact fluctuation as it changes so fast) but with the controller end of the resistor out of circuit the voltage is a steady 285vdc when measured there.

From this can we deduce that the controller is causing the wild fluctuation in DC voltage and if so, is it normal?

I notice a very small surface mount decoupling cap on the Vin line - could it be faulty?

[bbjunkie]

Re: Technika LCD19DVDID dead

After shorting G to S I'm seeing a voltage drop of .5v slowly dropping to .3v between D and S

Does this mean it's faulty?

It's faulty now alright!

Dropped my capacitor discharge resistor into the primary side while attempting to discharge the main cap. There was a crack as one end hit the MOSFET and now the test (out of circuit) shows a constant .5v drop

Will get one ordered and continue this in the new year.

Happy new year guys

Jim

[tom66]

Re: Technika LCD19DVDID dead

Sorry, I've been busy over new years with limited internet access. I've said it before; I think the problem is your power supply isn't getting enough power to continue running once started up. Causes include overload on the output, shorted diode, shorted cap (rare), open MOSFET (rare), bad controller IC, or even a bad transformer (rare), among others.