Telefunken TPM-420FHDB Audio no picture

[Grunder]

Hi Guys, been repairing Lcd's, but sending Plasma's away.

Now attempted to repair Telefunken TPM-420FHDB plasma, but got stuck, please help.
Set switches on audio, no picture. (red led with mains in, then green led when pressing stdby button).

Va = 55v
Vs was 199 adj to 205 (photo 3)
Vsc was -187.8 adj to -193 (photo 4)
Vg = 15v
Va = 54 (should be 55v)
Vs on = 3.2 ( photo 2)
Vs + Vsc scoped (photo's) 6+8)

I see there is what I guess are two cpu pcb's one with the external inputs, and one that communicates to the Ysus & Zsus. The 15v Vg does get there, and so does the Vs on. So why am I not getting any illumination? Please Help.

See other photo's

[ReeceyBurger123]

Re: Telefunken TPM-420FHDB Audio no picture

Seems odd that you dont get any panel emission as the sus voltages are up, do the voltages stay present and dont fluctuate rapidly or drop out ?

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

There was/is a slight movement on the meter, say like 193.5 to 194.0 before I adjusted the Vs adjustment, but not a big fluctuation, or should it be rock steady? I also switched the light off (a bit of day light seeping in), but see absolutely no illumination at all.

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

I also scratched in my scrap pile, and found a replacemrnt Ysus, zsus, & that smaller board i refer to as the logic cpu. I replaced them one at a time, but have the same result. I have reversed the order I replaced the pcbs, but back at square one. I know some might frown at just replacing pcbs without a diagnose's first, but i didnt think it would hurt?

[ReeceyBurger123]

Re: Telefunken TPM-420FHDB Audio no picture

Well looks like the buffer has some sort of SMP built on to it, however the Ysus and Xsus share the ERC so if Xsus is bad it can make Ysus look failed but the chances of that are little as you have the main sustain voltages. I would start by checking the buffers for short circuits after that then check the Xsus and Ysus for shorts. Also did you check VE on the Xsus ?

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

A bit confused here? I thought Ysus sometimes called x main & zsus sometimes called ymain. So the ve voltage would be on the board on the left or right looking from the back?

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

Sorry silly question, the Ve measures 97volts..

[ReeceyBurger123]

Re: Telefunken TPM-420FHDB Audio no picture

The names variate between the brands but they do the same job:
Ysus names:

Ysus(Lg, Fujitsu)
Ymain(Samsung)
Ydrive(Pioneer)
SN/SC(Panasonic)

Xsus names:

Xsus(Fujitsu)
Zsus(Lg)
Xmain(Samsung)
Xdrive(Pioneer)
SS(Panasonic)

As you have Ve I would say the Ybuffer is the fault you should remove it and test. Also make sure there are no cracks in the panel.

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

Thanks, for clarification, have in the interim fitted other ybuffer( i've obviously scrapped one of these sets before). I appreciate that a replacement board could also have the same fault, confusing the issue. I will check original board for short circuits.
I now remember why I stopped taking plasma's in for repair.
With a Crt an open heater would give the same result.
Is there a similar "element" in a plasma panel that would cause it not to illuminate although all the voltages & "drive" were present.

[ReeceyBurger123]

Re: Telefunken TPM-420FHDB Audio no picture

Nope the panel if given proper drive signals will always work only unless its cracked.

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

Hi, Sorry slow response, an other distraction.

Yes thanks Reecey, there was a short on the buffer board. The output of (U4509 see photo) a KA7805R 5.5v regulator read 2.5 ohms to gnd. I traced the short to (u5419 see photo) UM7410 1Kv Quad channel digital isolator pin 16, which I changed but alas the symptom remains. The 5.5 volts came up, but I guess either the one I fitted was faulty, or that there is other damage?

I Googled the UM 7410, but only found a UM7440.

Should I pursue the issue, the availability of the ic & the possibility of the panel being faulty make me think not??

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

Duplicate removed

[ReeceyBurger123]

Re: Telefunken TPM-420FHDB Audio no picture

Awesome you should remove the Ic and retest it. Also the PANEL IS NOT FAULTY ! Plasma Panels will never fail unless cracked.

[Grunder]

Re: Telefunken TPM-420FHDB Audio no picture

Thanks, will put one side, catch up with other repairs & get back, ciao for now.