Telefunken Vegas 42" plasma TV not starting

[angelos]

Hi guys. I have another set with a very unusual fault. When inserting power to the set i notice that after a few seconds the standby light starts flashing rapidly but there is no picture on screen. You do hear a relay click in, thats all. I found many caps bloated, some other with high esr. I changed about 15 caps on y-sus, x-sus, psu and main av board. This made no difference. I then stripped the tv until i got to the logic board and noticed the following. Upon powering up the set, the led on the logic board makes one quick flash... then comes on continuously for about 4 seconds and goes off permanently. The VS-ON pin going to the PSU does activate for about 4 seconds. Va = 55, Vs = 205 and Vscan = -190. These are all spot on according to plasma label. I checked all fuses and two green micro fuses and they are good. I checked all mosfets on y-sus and X-sus and y buffer... could not see any shorts. I then checked voltage regulators on main av board. It has two LM1117 regulators both being supplied with +5.2V. One steps diwn to 2.5V but the other steps down to 3.16V. I thought this to be strange and replaced the LM1117 with another one but got the same 3.16V. The output of the LM1117 measure in the kilo ohm range so no short there.
What i notice is that the tv starts up but the logic board shuts down the y and x boards. Some error i cant identify. Is there something else i can check or test?

Kind regards

[R_J]

Re: Telefunken Vegas 42" plasma TV not starting

The LM1117 is available in 1.8v, 2.5v, 3.3v, 5v, and adjustable version. they are not interchangeable

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

The LM1117 is available in 1.8v, 2.5v, 3.3v, 5v, and adjustable version. they are not interchangeable

Yes i know, on the above mentioned tv it uses the two resistors which control the ADJ pin on the voltage regulator. It's just a bit strange at which it controls the voltage.
I still can't make sense of where to look for a fault. I might take oscilloscope readings on the y buffer board and see if i get the correct waveforms.
It has Yfr and Yrr test points.

[R_J]

Re: Telefunken Vegas 42" plasma TV not starting

When you first turn the tv on, do you get the precharge flash, the whole screen should give a slight glow for a few seconds.
Maybe post the model number

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

No. There is nothing. I did not notice any flash

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

I spoke to a friend of mine that suggested i replace all electrolytics on the main board. He had weird symptoms and it turned out to be a 100uf cap whose ESR measured fine but the capacitance was way down. I will keep you all posted on the progress of this one.

[R_J]

Re: Telefunken Vegas 42" plasma TV not starting

If you have a scope, use it to check the caps, if you see a lot of high frequency ripple its not doing its job and is liklely bad.

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Hi R_J, yes i went back to the main AV board as suggested by a friend of mine and replaced the rest of the electrolytics. You cant believe it but when the cap is connected in circuit the ESR value is good but take it out and you get 27 ohms. After replacing all the caps the TV started up and i could tune the RF channels. There is still a problem though. It seems some times when you start the tv the screen remains blank as before except that the standby light does not flicker anymore it stays a solid green color. I now need to investigate what exactly is not starting up. Will keep you posted on the progress.

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Just an update. After replacing all 26 caps on the main AV board the sets starts up correctly when its been running for a while but on cold start up the Vs volts And Vs-on volts from logic board fall away after the sets power button is pressed (4 seconds) and the sets sound starts without a picture. If however you put the set into standby and again on then it starts up properly and runs.How do i go about determining where the fault originates from. What would happen if i force the Vs-on pin going to the power supply when set is cold. I really dont want to blow mosfets. Has anyone done something like that?

[R_J]

Re: Telefunken Vegas 42" plasma TV not starting

That does sound like a bad capacitor, it could be a small one on the power supply for the vs supply, or maybe on the Ysus board. When you first apply power if the cap is weak it won't keep the supply running, but the next attempt the cap has not completely discharged and still has enough capacity to keep the supply running.
This happens in smps when the cap that keeps the vcc supply runing from the secondary gets weak.
Usually its a small cap like 4.7 -47uf 50 volt that goes bad and they don't look bad. Maybe like that small cap near the VS-ADJ control
Im not sure but this schematic might be close?

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Thanks R_J. I dont know how i never ended replacing that cap but check the picture i attached. This 22uf 50V cap had a above 100 ohm esr reading. I had loosened the one point of the cap to measure it reliably but never changed it. I have subsequently replaced it and am waiting for tomorrow morning when its really cold to start it and see what happens. Check pic.

[R_J]

Re: Telefunken Vegas 42" plasma TV not starting

That cap seems to be for a small smps ic that supplies a few voltages on the ysus

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

After a cold start this morning i realised that it was the cure. Done and dusted. I replaced 32 capacitors on this set. Whew.

[R_J]

Re: Telefunken Vegas 42" plasma TV not starting

Good to here, so that one fixed it. many times its those little ones that give trouble, they dry up and don't have enough electrolyte to leak or bulge so get overlooked.

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Yeah. I did measure it but must have been distracted and ultimately forgot to replace it.
Thanks

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Hi all. This set came back after 3 months with the same problem. To summarize, on power up the psu clicks on and Vs and Va are correct and there is no pre charge flash nothing... I need to measure with my scope to see if the y or x panels are working. I would like to know when measuring on these boards where do i connect my scope ground terminal. I will upload later pictures of the boards so that you can see. Do i connect to chassis ground?

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Any help, any body???

[angelos]

Re: Telefunken Vegas 42" plasma TV not starting

Anybody with plasma repair experience able to run me through this set?
I even shorted pins 3 & 4 on Z board (TCON) and i get nothing. Dont have waveforms or any info to help me diagnose where the issue is. Heeeelp.

[lookimback]

Re: Telefunken Vegas 42" plasma TV not starting

Post a picture of the logic board.