JVC TM-H1700G Crt monitor power supply issue - Page 1
Forum section: electronics / repair

author: belzrebuth
author_rank: Frequent Contributor
timestamp: May 02, 2023, 08:35:14 pm
content: Hi all,I've got a TM-H1700G that turns on but doesn't respond to any button presses or has an image.That's probably power related as far as I can tell but there are many things than can go wrong and I'm not sure on what approach I should follow.Upon power up the monitor stays at input B (led B is on), I can't switch it to input A or enter the menu, no buttons work except from the front power button which puts the monitor in standby mode.I have no static so no high voltage either; I do get a degaussing sound when I turn it on.Only sign of life is that I can hear a relay clicking almost periodically at an interval of 2-3 seconds so it's slow but steady; turns on and then off; it's not ticking like a SMPS trying to start.The monitor had two capacitors that were seriously leaking and bulging so I replaced them both thinking this might be the culprit but it's not. It's doing the same thing as before.Capacitors were C933 and C911 and they were both on the main PCB and were rated at 400V I'm not sureI'm not sure but it could be that the clicking relay is RY902 which incidentally is connected to C911.Anybody familiar with this monitor t could help a bit on how to proceed?I would think that I need to make sure the flyback is alive for starters.This does not seem like a very high hour monitor but then again how did those capacitors end up so bulged? Perhaps there is a short somewhere?I included a link with the schematics.I would REALLY appreciate any help on getting this thing up and running if it's possible.https://www.dropbox.com/s/opm50957tc2oau4/jvc_tm-h1700gu%2Cge_sm.pdf?dl=0

author: eurgenca
author_rank: Regular Contributor
timestamp: May 03, 2023, 01:52:19 am
content: Hello.Check ic 703 in, out and reset pin, check c709 and c706. Anyway ic 701 pin 11 is responsible for clicking relay.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: May 03, 2023, 10:56:14 am
content: IC703 voltages for pins (1,2,3,4,5) are (7.9, 5.9, 0, 5, 5 ) so as incsribed in the schematic.Pin11 seems low all the time the relay is clicking.The period of the relay click is bigger than I said above, the clicking is slower maybe once in 7-10 seconds or so.I'm not sure if the clicking relay is RY901, could be RY902..I haven't found the rush.sw signal responsible for the RY902 though.I measured the big 330uF 400V capacitor I replaced and there is no DC on its legs.Seems like the monitor does not power up properly.C933 which was 22uF I replaced with 47uF I don't know if that makes any difference..

author: eurgenca
author_rank: Regular Contributor
timestamp: May 04, 2023, 06:00:37 pm
content: ok. If pins 4 and 5 (ic703) have 5v then stb p.s.u. is working. Check if you have voltage on RY 902 coil. Maybe this relay clicking but not conducting. If 902 don't kick in C911 has no voltage.confirm which relay or both is/are clicking.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: May 04, 2023, 07:22:00 pm
content: The relay that's clicking is RY902; from the coil side it has 0.25 and it's get to 7.8 when on which is fine.From the switch side all I see is 0.5V or so..I'm measuring from DC voltage from chassis GND.I then measured all pins of D901 rectifier diode and they're all 0.3 to 0.5VDC.It seems that no voltage reaches the rectifier?edit:I measured R902 and it's open.It's a 15W 4R7 ceramic resistor.How would it go open?Maybe C911 becoming a resistor of some sort would draw too much current?

author: belzrebuth
author_rank: Frequent Contributor
timestamp: May 04, 2023, 07:53:25 pm
content: I replaced R902 with 2* 8.2ohm 10W in parallel and I've got a picture!This should be good enough for testing.I still wonder how this big resistor got open though..I replaced those two capacitors I mentioned in my first post perhaps one of those was requesting a bigger current and now that they're replaced it's all good?

author: eurgenca
author_rank: Regular Contributor
timestamp: May 05, 2023, 05:11:34 am
content: I am glad you solve a problem.