JVC CRT PVM TM-H150CG : No HV - Page 1
Forum section: electronics / repair

author: snow_sg1
author_rank: Newbie
timestamp: May 26, 2021, 09:30:33 am
content: Hi,I've just got a JVC Hi res CRT pvm from 2004. The picture was really dim, brightness and contrast has almost no effect, and geometry was a bit out.I took it apart and it seem to be a high hour monitor, it was very dusty around the FBT area. So, I clean everything up and touch up some cold solder joints around FBT and CRT neck board. I desolder some caps to check them out using my components tester, they we're fine. Now I put the monitor back together and the standby PSU works, there is the degauss and then I hear the relay click, and within a second it click again. The cycles repeat every 20 seconds. Degauss, Relay click, another click.I'm sure they're is no HV at all, nothing on HT pins and neck board. I don't ear the oscillator either, which would explain the no HV condition. I've got voltage at the main transformer on primary side but nothing on secondary which is strange since the CPU must be running as the led lights up in front. But maybe I shouldn't measure the secondary side using chassis ground ? I'm at a loss. Maybe check oscillator first ? Can someone help me please, I'm good in electronics but not CRT stuff I'm afraid, I'm more into VCR and cameras.Thanks,Nicolas

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 26, 2021, 10:10:30 am
content: Quote from: snow_sg1 on May 26, 2021, 09:30:33 amThis is a symptom of too low anode voltage. So you had a HV problem to begin with. Perhaps a dead line transformer.Secondary problem could be that the cathodes and heaters are worn, PVM tend to be in continuous use, so the CRT might be at the end of its lifetime. This is unfixable. You can squeeze some extra lifetime out of it by increasing the heater voltage from 6,3V up to ~7V, at the risk of blowing the heater.If you want to repair this, you will need an insulation transformer, a scope and a high voltage probe.The constant degaussing points to a safety circuit triggering in the power supply (usually a simple PTC back when this was built). If you are really lucky, only the PTC is dead and prevents the power supply from getting enough energy.

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 26, 2021, 12:03:40 pm
content: replace flyback transformer with 60w bulb then tell us if power supply outputs are steadyi guess you made a short on the pcb or why not, damaged some capacitor when you remove/replace him.electronics don't just die if you took out a cap and replace himhigh voltage cleaning serves only aestetics, hv is not bothered by dust, but humidity or liquid or damaged insulation in hv area.so 'no hv' after some component removal and test have no real direct logic

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 26, 2021, 12:07:54 pm
content: and by the way, dim picture means low hv or some polarisation problem or video problem or power supply problem.NO HV means NO PICTURE at all, zero, nadabefore touching those caps, have you tested if fbt focus potentiometer works? this alone is a quick test on hv part, or measure the focus voltage, more simple then hv itselfand i repeat, no hv if you got others working means no image, the electrons never ever hit the screen

author: snow_sg1
author_rank: Newbie
timestamp: May 26, 2021, 10:37:27 pm
content: Hi,Thanks everyone for replies.More info on PVM, it was home use only and only attached to a DSR11 I got with it. The DSR 11 has 1100h of operation, so the PVM has the same amount. CRT must be good, brightness and contrast issue must be something else.First of all, maybe I wasn't clear enough.At first I had picture (dim and no brightness/contrast settings), then took it apart for cleaning and checking caps, because I think that it had issue with screen cap due to no contrast and kind of lines on osd text (not retrace lines)Check 4 caps which were good on my esr meter and capacity wise were withing specs. Re did some cold solder join, nothing else.I've got an isolation transformer, a rigol DS1054Z oscilloscope and the service manual of the monitor.I just need guidance in what to test first.I know that there is no oscillator running and no flyback, but I don't know whyI did a small video explaining the issue that you can find below, and what the screen is doingThanks everyoneHere's the video :https://youtu.be/588QgKWoKOg

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 27, 2021, 11:05:52 am
content: hi,voltage on pin 7 is powering your smps ic, if you got there something it means smps ic oscillates, you should get pwm on transformer pin 4 (ic output from his power stage)you don't really need the oscilloscope, it can be diagnosed 100% with multimeterchange ALL electrolitycs on hot side like C1012, verify for shorts on transformer outputs (after the rectifier diodes of course, this may be done first of all)sometimes the str chip can die but check other components firstput the smps schematic on the thread, it'a simplier to show you some 'checkpoints' on various components

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 27, 2021, 01:41:46 pm
content: Please link the service manual if you can so we can take a look at the schematic.

author: snow_sg1
author_rank: Newbie
timestamp: May 29, 2021, 09:46:34 pm
content: Hi,Thanks everyone for these quick replies.Here is the service manual linkshttps://www.manualslib.com/manual/1285597/Jvc-Tm-H150cg-E.htmlPSU schematics is at page 44 of PDFIf you can point me to what to check firstThank you so much !

author: vk6zgo
author_rank: Super Contributor
timestamp: May 30, 2021, 02:37:28 am
content: "While I'm in the area", a quick check on whether your CRT type monitor is producing EHT to the CRT is to rest your forearm against the glass on thefaceof the screen (the side you view the picture from).If EHT is present, the small hairs on your arm will be attracted to the front of the screen.Some faults produce EHT for a fraction of a second, on "turn on", then stop doing so.The "arm hair" test will also show this happening, & may give you a few clues as to what is happening.Another common sign of EHT coming on is a low "rustling" sound, audible in a quiet room.

author: snow_sg1
author_rank: Newbie
timestamp: May 30, 2021, 12:06:36 pm
content: Thanks for reply, I've checked, I'm sure there is no EHT at all, even at startup

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 31, 2021, 07:57:43 am
content: first check, do you got steady B1 == 53V pin 1 FBT? if you don't, we'll gonna lokk into IC1901 power supplysecond, Q1521 has pulses on base? (scope will tell you for both cases yes or no)reset your approach and take it from defect to solutionotherwise, normally you start by verifying al power supply voltages, from standby to the higher onesyou didn't answer my questions regarding diagnose of that power supply with IC1901, if secondary voltages are ok when you power up the monitor and IC1901 voltage rail see C1912if you don't come up with voltage measurements, we cannot helpmethods like put your backpalm near the screen, i won't comment...

author: vk6zgo
author_rank: Super Contributor
timestamp: May 31, 2021, 08:20:51 am
content: Quote from: perieanuo on May 31, 2021, 07:57:43 amIt works---sometimes all you need is a functional brain, other times you need every bit of help you can get!

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 31, 2021, 10:29:25 am
content: to Mr vk6zgo:yes it works but is doesn't tell you anything, the ps may be put in error mode caused by a short from other voltage line, no necessarily the hv area, so the op author as a beginner will be chasing ghosts

author: vk6zgo
author_rank: Super Contributor
timestamp: May 31, 2021, 12:23:05 pm
content: Quote from: perieanuo on May 31, 2021, 10:29:25 amIt tells the OP if EHT is being generated at all, & can even determine if there is a fault in the associated circuitry which will still allow a brief burst of EHT at turn on, meaning a reasonable chance that the EHT transformer is OK.I agree that if it is already established that one or more of the supply voltages are missing to that part of the board, that it won't help, but if that isn't known, digging round in earlier stages won't really help much, either, for someone who seems to already be "chasing ghosts".Anyway , I'll leave you with it, ---------I spent too many years messing with such things, & am "too long in the teeth" to enjoy fault finding by proxy.

author: perieanuo
author_rank: Frequent Contributor
timestamp: June 01, 2021, 08:18:20 am
content: Quote from: vk6zgo on May 31, 2021, 12:23:05 pmevery diagnose starts with ps/ps load check, not with putting the back of your palm near the screen. you're either off the chart either too much vanity, can't discuss technique like this.btw, i wasn't 'diiging around', i proposed diagnose for hv ps earlier, op had no reply.i will talk from now on with author

author: snow_sg1
author_rank: Newbie
timestamp: June 01, 2021, 01:47:06 pm
content: @perieanuoThank for your reply.I'll check tonight and let you know. I'm sure there is no voltage (B1) on flyback pin 1.I'll check transistor and IC with the scope to see if there is oscillation. I'm sure the issue is on the SMPS side, but I just don't know where to start to tackle the issue.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: June 02, 2021, 10:48:01 am
content: I am confused. In post #4, you show a monitor with a dim display yet you say you have no EHT?If in fact it does show the picture above, have you ever adjusted the screen control G2 to the CRT? That would certainly brighten it up.

author: snow_sg1
author_rank: Newbie
timestamp: June 02, 2021, 01:40:43 pm
content: Yes at first it did turn on.At first I had the picture you've seen above. It was way dimmer IRL than on the picture.I took it apart for cleaning and testing caps. Because, you don't see it in the picture but there was a shadow on OSD text and no action of contrast/brightness control. I wanted to look at the screen cap.I've de-dsoldered 4 caps, all were within limit both capacity wise and ESR wise. I've cleaned the chassis and put it back in place. I also took the time to fix some cold solder joins, especially on EHT.Everything is plugged back as it should.Now the power LED lights up, you can hear the degauss and relay click. But they're no EHT, can't switch input, no sound, no voltage any of EHT pins.They're is a click from the relay of the standby PSU every 20 seconds or so. Nothing elseI hope that this clear everything up

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: June 02, 2021, 09:30:52 pm
content: Yes it does.It seems that the LV power supply isn't coming up.Do you have a capacitor in backwards? I have seen where the board is marked wrong.I used to take a black Sharpie and mark the board as I watch the caps come out. Sneaky Japanese manufacturers.Hopefully, you can check the schematic. Much better with pictures.

author: snow_sg1
author_rank: Newbie
timestamp: June 02, 2021, 10:12:58 pm
content: Hi,So, I’ve done some test.SMPS :Transformer T1901Pin 24. I have 126VAC (see capture 1)Pin 67. I have 126VAC. Mirror DC (see capture 2)Output pin 10,11,12,13,14,15,16,17,18 = nothingNot relevant since nothing on transformer outputFBT pin 1 (B1) = nothingBase of Q1521 = nothingThanks,Best regards

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: June 02, 2021, 11:20:07 pm
content: Tell us if everything checks out voltage wise in the LVPS as shown.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: June 02, 2021, 11:24:37 pm
content: And the shutdown/feedback circuit.

author: feded
author_rank: Newbie
timestamp: May 20, 2023, 04:02:12 pm
content: Hello, did you ever manage to solve this? I got a TM-H150cg with the same problem you described at first, dim picture. If I tweak brightness and contrast up, I get streaking in some objects. Image attached appears to be vibrant, but it is not. I got a TM-H1700g with perfect brightness and contrast to compare, so I know there is something wrong with the TM-H150cg

author: FIXITNOW2003
author_rank: Regular Contributor
timestamp: May 24, 2023, 06:45:27 am
content: have you checked feed resistor to standby regulator R1922 it often go high resistanceR1922 should be 560K 1/2W MF

author: feded
author_rank: Newbie
timestamp: May 26, 2023, 07:47:57 pm
content: Quote from: FIXITNOW2003 on May 24, 2023, 06:45:27 amThanks, I'm gonna check it tonight