tv repair help - Page 1
Forum section: electronics / repair

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 21, 2013, 02:04:29 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: October 21, 2013, 02:34:36 pm
content: 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.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 21, 2013, 02:47:48 pm
content: thank you for that. I got my phone to upload a pic now. that is the area where the clicking is coming from.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 21, 2013, 03:17:57 pm
content: Only board number I can find is ggb90006 -001dh

author: tom66
author_rank: Super Contributor
timestamp: October 21, 2013, 03:30:20 pm
content: 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.htmlThat 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?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 21, 2013, 04:29:27 pm
content: woops, clicked the link, downloaded something but cant find it. Now it wont let me do it again lol. blody merphy.

author: tom66
author_rank: Super Contributor
timestamp: October 21, 2013, 05:02:36 pm
content: Here, I uploaded it to my SM sitehttp://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

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 21, 2013, 05:18:04 pm
content: Thank you tom, I will let you know the out come.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 01:50:14 pm
content: 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 w9704witch then goes to c9593 and c9592

author: tom66
author_rank: Super Contributor
timestamp: October 22, 2013, 02:37:58 pm
content: 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.Quote

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 05:00:56 pm
content: 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 voltageswere 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

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 05:15:28 pm
content: 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.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 06:35:56 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: October 22, 2013, 06:43:00 pm
content: 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.

author: wraper
author_rank: Unknown
timestamp: October 22, 2013, 07:32:00 pm
content: 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.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 07:46:03 pm
content: 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.

author: Alana
author_rank: Frequent Contributor
timestamp: October 22, 2013, 07:52:03 pm
content: bad solder or bad diode in mains rectifier?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 08:01:25 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: October 22, 2013, 08:20:21 pm
content: 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...

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 08:58:17 pm
content: ok tompin 5 and 10 are both 3.2v and nothing on lb-pro

author: tom66
author_rank: Super Contributor
timestamp: October 22, 2013, 09:09:02 pm
content: 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.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 22, 2013, 11:11:28 pm
content: 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.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 12:00:14 am
content: that 375v net is 330v not 180 odd like I said, I was using gnd2 not gnd1 oppsbut still 45v low

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 10:36:35 am
content: 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.)

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 02:21:57 pm
content: 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.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 03:10:36 pm
content: pon in faulty state is 0v. voltage accross e&c of pc9502 in faulty state is 20.6vacthe 375 net is 336.5v

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 03:16:29 pm
content: You using VAC or VDC? You should use VDC.The PON signal going high should cause the C-E voltage to drop very low, under a volt, so the reading doesn't make much sense...Note E&C of PC9502 are on primary side not secondary side.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 03:31:21 pm
content: the part is this way up in the tv I measured the left side. Its 0.1 dc and the right side is 0.6dc

author: wraper
author_rank: Unknown
timestamp: October 23, 2013, 04:35:41 pm
content: Quote from: snipersquad100 on October 23, 2013, 03:31:21 pmWhy the hell you are measuring voltage between primary and secondary. That can be dangerous BTW.

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 04:35:54 pm
content: Hah sorry for the confusion but the CATHODE pin is often called K to avoid confusion with the collector pin. So you need to test across the collector and emitter on the primary side. There is no electrical connection between the primary and secondary of a power supply like this.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 04:41:46 pm
content: that's my fault sorry across pins 3 and 4 of pc9502 is 0.09vdc

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 05:08:58 pm
content: Is that working or faulty?If faulty, that indicates the opto is fine and the fault is somewhere on the transistor hanging off the PON line, I suspect.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 05:13:35 pm
content: that's when it was working. That noise I can here is coming from Lf9002 according to the mrs.

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 06:03:49 pm
content: OK, that's good. Just wait for it to fail to make sure it's not the opto. Looks like it's somewhere around the area switching the Vcc, so should be easy enough to trace down (hah, famous last words...)

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 07:58:37 pm
content: the voltage across pins 3 and 4 of pc9502 when faulty is 0.1vdc. so what do you think it is?

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 08:24:26 pm
content: The opto is fine, then. There are a few things that may be pulling down the PON signal.The voltage across C9511 should not exceed 11V, what does it measure? (I'm basing this on the MAB100 zener diode being 10V rated.)Q9503 can cause PON to be pulled low, caused by voltage at end of one end R9519 (relative to 450V capacitor negative lead) being lower than approx 0.7V. I'm hoping R9519 is through hole.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 09:54:54 pm
content: c9511 is 10v. r9519 is smd I cant get a ohm reading across it but I can with another 474 smd resister, could it be cos its in circuit?

author: tom66
author_rank: Super Contributor
timestamp: October 23, 2013, 10:43:54 pm
content: You should still be able to measure a resistance, even if it is in circuit. It could be cracked/damaged maybe? And that could cause your intermittent issue.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 23, 2013, 10:54:35 pm
content: I pull it out tomorrow, im off to bed. thanks mate for you help.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 07:49:22 am
content: I doubt that there are any cracked parts. I there would be such, board should react to bending and defect should be stable enough without it. I say again, check the capacitors. It is very common for them to cause intermittent issues when they are almost dead. When device fails to start but works normally if it managed to do it, 90% that this is faulty electrolytic capacitor. And problem becomes worse with time until device stops to work completely.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: October 24, 2013, 08:56:24 am
content: This post might help.http://www.justanswer.com/tv-repair/7kz6q-jvc-lt-42x579-trying-trouble-shoot.htmlAs already suggested its usually,but not always the caps,and they are cheap enough to replace anyway,and saves doing it at at later point.Good luck with it.

author: tom66
author_rank: Super Contributor
timestamp: October 24, 2013, 09:57:24 am
content: Bad caps are very unlikely on this actually-made-by-JVC TV because it uses entirely high quality capacitors: Rubycon mostly with a few Nichicon. Yes while even good capacitors fail their failure rate is so low it's NOT a good idea to shot-gun replace them on the board, you'll just waste time. Out of nearly 60 (hobby) TV repairs I've had maybe 6 or 7 bad capacitor replacement jobs... It's a common suggestion on the internet "have you replaced the caps?" but it's nearly irrelevant if you aren't talking about a Samsung or LG made in 2007~2008.Bad capacitors also cause odd symptoms. A bad startup capacitor could cause this problem (by checking the voltages across them that has been mostly ruled out) whereas a bad output capacitor would tend to cause low output voltages rising after warming up, flickering backlight, distorted audio, glitches on display, etc.The particular fault could be caused by a leaky transistor, intermittent resistor (SMD resistors can become intermittent) or some other problem along the PON circuit.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: October 24, 2013, 10:37:11 am
content: Yes,the capacitors should be good ,i thought i might get shot down for suggesting replacing them.If i have them in stock i replace them anyway and test the old ones,any any that test good i reuse.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 10:58:49 am
content: I replaced not so small amount of faulty "good brand" capacitors in SMPS. Being Nippon chemi-con, Rubicon or whatever does not guarantee them to be fail proof. They still remain the most unreliable components, they just don't fail in tons like crap ones. I didn't suggest to replace big ones on secondary side BTW, that is the place where crap ones fail usually. What I see from those symptoms is bad capacitor on PWM controller power rail (or something like that) and protection kicking in. And do you really think that "intermittent resistor" is more possible that faulty capacitor. What fascinates me that you just throw away the whole idea of faulty capacitor just because it is JVC, Badcaps don't write about that, Rubycon... That can be fast and dirty repair but can became a real PITA for OP with such suggestions. OP doesn't seem to be very familiar with electronics and I believe suggestions must be that he should do easiest things first before digging deeper. I'm sorry If I hurt your feelings but that's what I think.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 02:24:50 pm
content: ok I pulled out R9519 and its 470k dead. Ive changed the caps but to no success. This Lf9002 is making a loud buzzing noise, its only an duel coil or inductor im not 100% sure. I also changed ic9501 but still nothing. I would like to change that Lf9002 before I take this to the tip but I cant find the part anywhere. Any more ideas before it goes to the tip lol. ive danted with it.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 02:27:36 pm
content: this is the part where the buzzing is coming from.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 02:47:06 pm
content: Quote from: snipersquad100 on October 24, 2013, 02:24:50 pmDid replacing R9519 change anything? As I read circuit PFC won't start with it being open. That buzzing coil is just mains filter. You can also try to unsolder collector of Q9503 and swith on, then measure 375V rail to see if PFC works.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 03:01:25 pm
content: I didn't replace R9519 it measured 470k so I put it back in. Whats pcf mean? i'll pull up that collector now. the 375v rail has got 335v has it goto be 375?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 03:12:51 pm
content: I cant lift that leg with out braking it, it's a tiny smd one with no number on it so I don't know witch one is the collector anyway.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 03:13:13 pm
content: That 470Kkdead looked as dead for me, not native english speaker. OK, if that resistor is ok no need to unsolder that transistor. Just measure voltage Between GND1 and collector of Q9503, collector of Q9502, emitter of Q9507 and pin 8 of IC9502. All in working state, no need to measure faulty.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 03:26:38 pm
content: Quote from: snipersquad100 on October 24, 2013, 03:12:51 pmYou can figure it out by whith other parts are connected to tat pin according to schematic. For example, if pin of Q9503 is connected to Q9502 and R9521, this is collector. And Usually collector is single pin in the middle of smd transistor. Look at the picture.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 03:27:59 pm
content: which one is the collector lol, 1 2 or 3. I cant find a datasheet on it as It got no number.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 03:29:12 pm
content: oh ok ingnor that 123 pic

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 04:14:47 pm
content: ok, C of Q9503 = 0.01vC of Q9502 = 4.5vE of Q9507 = 17.2and pin 8 of Ic9502 = 17v

author: tom66
author_rank: Super Contributor
timestamp: October 24, 2013, 04:25:01 pm
content: Whereabouts are you in the UK? If you're near me, I would actually pay money for this faulty set as described. If you give up on it...Your ground for primary side where do you have it?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 04:30:25 pm
content: im in Swansea. I used the -side on bridge rectifier as it says gnd1 on the schematic.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 04:33:33 pm
content: In that section everything seems OK. As I understand at the same time there is only 330V on 375V rail. So I need some more checks. Please measure voltage between GND1 and pin 1 of IC9502. Then measure voltage across C9503 and across C9501. If voltage across capacitors is almost the same (what means PFC is really dead), switch TV off and then measure resistance of K9502 fuse, R9529, R9530, R9502. Be sure That C9501 discharges before measuring those resistors and fuse.

author: tom66
author_rank: Super Contributor
timestamp: October 24, 2013, 04:33:48 pm
content: Quote from: snipersquad100 on October 24, 2013, 04:30:25 pmLol, OK. Leeds. I used to live down near Reading so I would pick it up otherwise. But anyway, even if you decide to get rid of it, it will be gone the next day if listed on gumtree for £30 as faulty...The HIGH ignal at collector of Q9502 is good, this will turn on Q9508 which should turn on Q9507.So what do you get at C of Q9507?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 05:49:22 pm
content: Gnd 1 to pin1 of Ic9502 = 2.5vC of Q9507 = 17vV across C9503 = 330vV across C9501 = 332vResistanceK9502 = 0.09 ohmsR9529 = 100 ohmsR9530 = 22.09 ohmsR9502 = 0.2 ohms

author: tom66
author_rank: Super Contributor
timestamp: October 24, 2013, 05:52:01 pm
content: You should have 375V if that is as it is. If not, IC9502 may be defective, you replaced it? If so check C9502 for int short, try flexing it.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 06:10:05 pm
content: Strange that there is 2,5V on pin 1 as there should be 2,5 at 375V output as it is feedback pin and only 2,2V on 330V. So Either there is something wrong with sense voltage divider or ic9502 is dead. Check R9514 and R9515. Their resistance in paralel should be 16,6 kOhm, however surrounding circuit can influence it. Check also R9512, R9513, R9516. I think we are very close to find the fault.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 06:56:30 pm
content: R9514 = 16.2 ohmsR9515 = 16.2 ohmsR9512 = 828k ohmsR9513 = 780k OhmsR9516 = 780k Ohmsthe last 3 readings were up and down, might be cos they in circuit.

author: tom66
author_rank: Super Contributor
timestamp: October 24, 2013, 06:57:49 pm
content: Do you mean 16.2 kohm or 16.2 ohm really?

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 07:02:25 pm
content: 16.2k sorry on both

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 07:06:34 pm
content: yea I changed that ic today same fault. yesterday I paralleled up that big cap with a 470uF 450v cap, no change. its tight to the pcb and solder looks ok, I did resolder it yesterday too.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 07:14:31 pm
content: c9501 I ment, I check c9502 now

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 07:25:52 pm
content: Quote from: snipersquad100 on October 24, 2013, 06:56:30 pmThat's strange, because they are in series and all 820K so should read the same even in circuit. Try to desolder R9512 and check resistance. Then check 2 remaining resistors as they are no longer connected to the circuit and must read real value. Look also what is written on them, they should be the same 820k but who knows. And measure R9514 again before soldering R9512 back.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 07:51:12 pm
content: ok,R9512 = 822k numbered 824R9513 = 787k nr 824R9516 = 778k nr 824that's not right surely ?

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 07:59:04 pm
content: Yeah, 2 resistors are way off, and strangely to lower side what is not usual. Thats seems to be the fault. Replace all 3 to new ones as there is potential that 3rd resistor will go bad later. Better use 1% resistors as a replacement or if you use 5% ones check them before soldering that total value of them in series would be not worse than 2460 kOhm +-1%

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 08:03:13 pm
content: im going to have to order them, unless I bodge it up with throu hole lol

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 08:17:33 pm
content: Quote from: snipersquad100 on October 24, 2013, 08:03:13 pmWell, you can bodge temporarily to see how it works.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 09:03:16 pm
content: The 375v rail has gone from 345 to 383volts, ive just turned it on, fingers crossed, touch wood lol.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 09:18:53 pm
content: It's Still on, I think it's safe to say its fixed.Thank you guys.

author: wraper
author_rank: Unknown
timestamp: October 24, 2013, 09:44:34 pm
content: Happy for your succesfull repair

author: tom66
author_rank: Super Contributor
timestamp: October 24, 2013, 09:55:47 pm
content: Nice, interesting to see the failure of the resistors to decrease in value rather than the typical increase due to excessive heat.

author: snipersquad100
author_rank: Frequent Contributor
timestamp: October 24, 2013, 10:13:02 pm
content: It has been interesting, ive enjoyed doing it step by step and have learned a lot. Thank you.