tv repair help

[snipersquad100]

Hi I got a jvc lt42dg8bj lcd tv, it works fine some days an others times it will turn off, with no sound or pic just power light on, screen is perfect when working. I've taken it apart and there is clicking by the blue Plastic Film Capacitor # (6h225k) witch alters frequency when I move it slightly. I've never heard a cap to click before. I took out the cap and it measuring 2.3uF, which I think is within tolerance. Has anyone heard of this before? I'd post pics but my phone is not uploading for some reason.

[tom66]

Vestel inside? 17PWxx boards?
badcaps.net is a great place for more specific tech support.
Get your board numbers (17PWxx and 17MBxx) and I will get you schematics and any service manuals available.

[snipersquad100]

thank you for that. I got my phone to upload a pic now. that is the area where the clicking is coming from.

[snipersquad100]

Only board number I can find is ggb90006     -001dh

[tom66]

Ah, wow. It's a *real* JVC not a supermarket sold-brand-and-rebadge job (as all new JVC TVs today are, shame.)
Schematics:
http://elektrotanya.com/jvc_lt-42a80_lt-42da8_lt-42dt8_bj_sj_su_u_zj_zu_sch.pdf/download.html

That capacitor looks to be PFC decoupling after bridge rectifier, probably NOT the cause of your issue.

What you need to do is monitor PSU output voltages when it works and when it fails to work.

Also, please detail the exact fault: when it fails, do you get power light, does set -try- to turn on (e.g. you would know if power LED changes colour or flashes), do you get backlight, do you get sound? If it fails, do you get a blinking power light which might flash a fault code?

[snipersquad100]

woops, clicked the link, downloaded something but cant find it. Now it wont let me do it again lol. blody merphy.

[tom66]

Here, I uploaded it to my SM site
http://www.toms-service-manuals.com/getfile.php?mode=viewpdf&req=JVC_LT-42A80SU_LT-42A80ZU_LT-42DA8BJ_LT-42DA8SJ_LT-42DA8SU_LT-42DA8ZU_LT-42DA81U_LT-42DT8ZJ_%5BSCH%5D.pdf&mfg=JVC

[snipersquad100]

Thank you tom, I will let you know the out come.

[snipersquad100]

ok, Ive put that cap back in, there still a buzzing noise, I think it coming from ic 9501 part number F9222L Its connected to a heat sink highlighted in the pic.
I was proding around with a screwdriver witch lights up if you touch a mains supply to see if I could find some vibration which is making this noise, and the heat sink is making the screwdriver light up. the heat sink is soldered to a ground net in between c9503 the cap I removed and wire link w9704
witch then goes to c9593 and c9592

[tom66]

A lot of power supplies go into a low power pulse mode when in standby.

Please answer my fundamental questions above; it's important to know if it is the power supply, main board or another part causing issues.

What you need to do is monitor PSU output voltages when it works and when it fails to work.

Also, please detail the exact fault: when it fails, do you get power light, does set -try- to turn on (e.g. you would know if power LED changes colour or flashes), do you get backlight, do you get sound? If it fails, do you get a blinking power light which might flash a fault code?

[snipersquad100]

Sorry Tom for the delay in answering your questions, I was waiting for it to go off so i could find out.
The led is solid green when working and was also solid green when it goes faulty.
The voltages on the conectors were all normal acording to the schematic you sent me but only the standby voltages
were present when faulty mode. I had no screen or sound when faulty. no sign of the tv trying to power back on.
Ignore the bit where I said the heat sink was live, I touched it and I'm still alive lol

[snipersquad100]

It seems to be pointing to that ic9501 as there's no power to ic9701 and ic9751 or across the photocouplers pc9501 and pc9502 on pin 23 of the ic9501 im getting 36 volts according to the schematic it should be 375 volts unless it means 37.5 volts.

[snipersquad100]

ah ha that 375 volt net is measuring 190 volts when the tv is working, so that net is low. so that takes it back to maybe the c9501 330 450v cap or maybe the l9501 inductor. I have bleeped out the L9501 seems ok but one of the 3 coils in parallel could still be down as I bleeped it in circuit.

[tom66]

When in fault state, check pins MAIN_POW and PFC_POW are logic HIGH (>2V.) Pin 5 & 10 respectively of CN900A. If they are it is a power board issue but if not, the TV main board is not telling the power supply to switch on so it will not be working as expected. This would point to a TV main board fault.

You should also try checking the rail voltages when it attempts to turn on and fails. See if they are low. Maybe LB_PRO is triggering & sending shutdown sig to main board.

[wraper]

I bet some small capacitor is dead on SMPS primary side. Try to replace electrolytic capacitors in blue circles, or check them if you have ESR meter.

[snipersquad100]

I will check those caps, but my guess is if it is the power board determined by doing what tom said, I think it be that big 330ohm 450 volt cap or the L9501  because the 375volt net is only 190 volts when the tv is working. But im no pro lol im just tracing back the 375v net.

[Alana]

bad solder or bad diode in mains rectifier?

[snipersquad100]

funny enough there was a dodgy solder joint on one of the pins on the bridge rectifier but it was still the same after resoldering. will put the scope on it tomorrow. thanks.

[tom66]

You're jumping ahead. You still haven't found out if it is even the power board at fault -- I have seen several JVC LCD TVs on badcaps forum with  bad main boards but none with bad power supplies yet...

[snipersquad100]

ok tom
pin 5 and 10 are both 3.2v and nothing on lb-pro

[tom66]

OK, that seems to point to PSU fault.
When faulty and when good, check voltage across: C9508, C9546, C9219.
Expect approx 18V across all three.

[snipersquad100]

ok c9508 is 17v working 0v faulty, I think u ment c9564 cant find a c9546 which is 17v working 14.5 faulty, c9219 is 20v working and 25.3 v faulty. Also I noticist that the bridge rectifier is still operating in faulty mode, I guess that's why the caps a still got voltage. when it goes off the speakers make a loud noise, shit myself as I was probing the ac across the bridge as it turned off lol.

[snipersquad100]

that 375v net is 330v not 180 odd like I said, I was using gnd2 not gnd1 opps  but still 45v low

[tom66]

That means the power factor correction is shutting off, which will cause the 375V (PFC output) to drop off to the mains input voltage. This will occur for a number of reasons but prime suspect is the signal which switches the Vcc to the PFC IC.

2SB1188 is a transistor which does this. It is controlled by OPTO PC9502. When MAIN POW is high, the LED in the opto lights, turning on its internal transistor. This pulls the collector voltage low releasing Q9558 to float PON high (through 68k near PFC IC.)

So, you need to check a few things: C-E voltage across PC9502 and the PON signal somehow, may have to solder a wire somewhere e.g. R9520 end near Q9508 (SMD.)

[snipersquad100]

ok that pon was hard work, its 4.5v working and the voltage across c&e on pc9502 is 31.2ac. im wait for the set to go faulty now to get the faulty state voltage.