JVC TM-1500PS no power

[ostlar]

Hi, I am working on a dead JVC TM-1500PS video monitor.
It is in great condition, other than it does not power on.

I need some help diagnosing it because I'm a little lost.

Upon power on I get green power LED and a relay click, a constant whining noise coming from the PSU, another relay click, and then silence and no power LED.
The relay clicking is RY501.

It does not want to try to power on again until the capacitors have discharged and power is lost from the PSU.

This what I've done so far:

- Checked for cracked solder joints
- Checked all the capacitors, resistors and diodes in the PSU
- Checked for shorts in the B1 circuit, flyback and deflection yoke
- Checked capacitors in horizontal and vertical deflection
- Checked for shorts in HOT
- Checked diodes and resistors in the B1 circuit
- Checked fusible resistors
- Disconnected the degauss coil

The PSU is on a separate board, so I am able to isolate it and test it.

I have measured the B1 voltages upon power on.
I get 84V while it is whining, then it jumps up to 129V after the relay clicks and whining stops.
The B1 upon operation should be 110V according to the service manual.
After the whining stops and RY501 relay clicks, I then have stable 129V on B1 and C521, while nothing else happens.

I disconnected the cable from the PSU to the main board and hooked up a 230V 100W light bulb (39Ω) to the B1 circuit to load test the PSU.

It draws 0,28A at 110V for a total of 30,8W.
This is less than half the power the monitor uses at normal operation (68W according to the specs) but the PSU handles it well.
There is some faint whining from it.

I added another 100W lightbulb in parallel for a total of 19Ω measured with the cables.
That results in 0,56A at 108V, or 60,5W.
The PSU makes a whining noise a bit more higher pitched than it did when I try to power on the CRT, but it seems to handle the load and somewhat keep the voltages up.

This is where I am kind of lost. There is no indication of a short on the B1 rail, but the power supply is acting like there is.

I'm kind of stuck as of now, been on and off on this project for a couple of weeks. Having some new eyes look at this usually helps.

[vol.2]

Originally Posted by ostlar

Hi, I am working on a dead JVC TM-1500PS video monitor.
It is in great condition, other than it does not power on.

Another important piece of information is whether or not the high voltage is kicking on or not.

Use a frequency app to see if you can detect a 15kHz spike when the set is switched on. Turn on the app, then watch what happens when you switch on power to the set. It might turn on briefly and then switch off when it goes into protection. Or it might just be on and fine. The app I use on my android phone is called Spectroid, but there are lots of them out there for free.

It the high voltage isn't turning on, then I would suspect that the B+ is correct at 129V because it's not being loaded. Your test with the bulb shows it regulates when it's loaded.

So check to see if you're getting 15.1kHz and then you'll know if the HV is working. That in itself won't tell you what to fix, but it will get you closer to a cause

The fact that you get 110V when you load it is also suggestive, but you also might have a weak power regulator IC (IC901), which could show issues only under load

Not sure if I can be of any more help, but hopefully that gives you some paths to check out