Sony PVM 2730QM - Power Supply

[sunomo1]

I'm trying to repair a Sony PVM 2730QM monitor. The picture flickered and I heard a strange electric noise. The source of the noise was the Power Supply board. I started the repair but now I get stuck.

I dismantled the board and I replaced C621 C682 R679 R683 since there was a burnt on them and C654 C655 R677 since they were faulty. Now I have these voltage values: 8V line 10.5V (not stable), 15V line 15.6V, 140V line 129.7V (it's enough?), +18V line 23.2V, -18V line -22.5V.

The sound is changed and now it's like a periodic cricket sound. I've read that it could be due to a non working transistor. I've checked them all and they seems to work, but not sure about their dynamic behavior.

When I attach this PSU to the monitor the tube degauses but it doesn't turn on. I also have a twin working PSU, and attaching it the tube turns on, even though the front panel is still disabled.

What I've to do to finish the repair? Schematics attached.

Full Service Manual: https://cdn.badcaps-static.com/pdfs/...15d3499bcf.pdf

[CapLeaker]

Re: Sony PVM 2730QM - Power Supply

What about C652 on the 140V rail?
when this cricket sound appears, what happens to all the voltage rails?

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

I've just swapped C652 with one from a working PSU, the result was that the working PSU was still working and this one still has same problems.

The cricket sound always appear when the board is on, and I get the voltages listed before. 8V is not stable, it ranges from 8 to 13, but the other lines are stable. Do you think that 129.7 is too low to start the tube (monitor neckboard)?

Tomorrow I'm going to randomly replace some transistors, even they're statically ok, don't know if it's a good idea.

[CapLeaker]

Re: Sony PVM 2730QM - Power Supply

Try heating up the PSU with an hair dryer. Just hot enough not to burn yourself. Plug the bad PSU in and see what happens.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

I've tried to heat the PSU but that cricket noise does not change. The problem is that the 140V line is not stable and it rages from 123V to 138V. Of course it's unable to power on the tube Why is that? D651 and C651 are supposed to be responsible of that? Or the problem is expected to be located before them?

[R_J]

Re: Sony PVM 2730QM - Power Supply

What about C620 & C622, either one of those could cause cause unstable voltage

[CapLeaker]

Re: Sony PVM 2730QM - Power Supply

sounds like something is breaking down / leaky. Can you maybe isolate where this noise is coming from (like a wooden cooking spoon etc to your ear)?
No. D651 and C652 are responsible for HV. C651 is a snubber cap. Swap C651 out and try again. Did you check D660?

[R_J]

Re: Sony PVM 2730QM - Power Supply

That 8 volt line should be around 12 volts as it supplies the 8 volt regulator with 11.3 volts on the [B] board Plug B20 (page33)
Q121 is the regulator transistor, collector = 11.3volts, base=8.1 emitter= 7.5 volts
That line also supplies ic121 +5 volt regulator ic
That line could be loading the power supply, thats why R677 opened
I would check that circuit.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Hi, thanks for your messages. I've replaced C620 C622 C652. I've checked C651 D660 and they're ok. On the +-18V lines I've 28.7 and 25.9 but it seems that they slowly increase. On the 8V line I've just 10.5 and on the 15V line I've 15.6. The 140V line is not stable and it still ranges from 123V to 138V. Very frustrating.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

The fault has to be found on the Power Supply Board. I've a twin PSU and plugging it into this monitor the tube turns on correctly.

[R_J]

Re: Sony PVM 2730QM - Power Supply

What voltage do you have on IC602? Have you tried swaping the Fc boards betwen the power supplies?

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

About IC602 voltages I have 103-104V on pin 1 and pin 9, 102-103V on pin 11 and 89-90V on pin 5. On the other side from pin 15 to pin 24 I have very low voltages, below 2V it's expected?

I've not yet tried to swap the FC board with the one from the working PSU because I don't want to burn it out. It should be safe to do that?

[R_J]

Re: Sony PVM 2730QM - Power Supply

IC602 is the optocoupler, It only has 6 pins, It is used to couple the signal from the secondary to the primary to control voltage regulation.
I don't know what ic you are mesuring for those voltages?
The schematic shows all voltage meaured to chassis ground, which is stupid for voltages in the primary.
If you can, check the voltage across D602 (12 volt zener), then with the negative probe still on the D602 anode, check the voltage on IC602 pin6.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Very sorry, my mistake.

Voltages on IC602 (to the ground):
pin1 0 V
pin2 1.4V
pin4 96-97V
pin5 90-91V
pin6 98-99V

When I touch pin 4 with the multimeter I hear an additional strange buzz.

Voltages on D602:
anode-catode: 11.6V
anode-IC602 pin6: 3.7V

[R_J]

Re: Sony PVM 2730QM - Power Supply

When I touch pin 4 with the multimeter I hear an additional strange buzz.

Thats because the meter negative should be on hot ground when checking pins 4,5 or 6.
The 1.4 volts on pin 2 seems correct according to the schematic.
on the opto's output (schematic) shows a 6 volt difference (you) measured a 8 volt difference. that might explain the lower secondary voltage.
Does the 140 volts change if you adjust RV651 (+B adj)
It should be safe to swap the fc board from one power supply to the other. there are a few electrolytics on that board that might cause a problem.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Ok, I've now swapped the FC boards, placing the one from the working PSU, but the 140V output is still unstable ranging from 123V to 138V. I think that the problem must be found on the FA board.

Rotating RV651 I have 120V (stable) on the 140V line and 11.3V on the 8V line. I think that the correct voltages should be around 141.6V for the 140V line and 12.3V for the 8V line (it's what I get on the other twin monitor).

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Should I replace IC602?

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Ok I've now replaced IC602 (taken from the working board) and tuned RV651. Now I have 143.5-144V on the 140V line 12.1V on the 8V line 15.6V on the 15V line a 27.8V on the +18V line and -30.5V on the -18V line. Unfortunately the non working PSU is still unable to turn on the tube even the output voltages seem to be almost correct. Indeed the working PSU is able to turn on the tube, even having the IC602 swapped. So the reason is definitely not related to IC602, I suppose.

[R_J]

Re: Sony PVM 2730QM - Power Supply

Ok, so you swaped IC602 from the working board to the bad board. Doing that resulted in the 140 volt line which was 120 volts, coming up to 140 volts, correct?
And you can vary the voltage with RV651 correct?

question #2
you installed ic602 from the bad power supply into the working power supply and it is still working fine and turning on the monitor, so ic602 is ok. correct?
I believe I asked before if C620 and C622 were replaced?

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Ok, so you swaped IC602 from the working board to the bad board. Doing that resulted in the 140 volt line which was 120 volts, coming up to 140 volts, correct?
And you can vary the voltage with RV651 correct?

Yes

question #2
you installed ic602 from the bad power supply into the working power supply and it is still working fine and turning on the monitor, so ic602 is ok. correct?

Yes

I believe I asked before if C620 and C622 were replaced?

Yes replaced brand new