Sony PVM 2730QM - Power Supply

[R_J]

Re: Sony PVM 2730QM - Power Supply

So have a good look at the schematic. The primary is switching to give you +140, It is also giving you the +18 and the -18 althogh they are high likely because there is no load on them.
So that leaves the winding 22,23,24. How can that winding be dead when the others are working?
You don't just have a problem with the 8 volt line, the line from D654 is also not working, the only reason you have +15 volts is because it is coming from the 140 volt line via diode D660 and R654

[CapLeaker]

Re: Sony PVM 2730QM - Power Supply

Lift one leg of D654 and R677. See if you get AC off the winding. Nothing could drag it down. The AC voltage will be lower, but it should tell you if something comes out there or not.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

I've lifted D654 and R677 and I see no voltage on pin 22,23,24. But please take in account that my meter cannot measure less than 1mV.

It's very unlikely that this winding is half dead. I've previously swapped it with that of the working PSU.

Comparing the voltages between the two PSU I saw different values of the high voltage area. Also the original burnt resistors were R679 R683.

Btw by lifting D654 and R677 any cricket sound disappear. It's reasonable to think that disconnecting them something on the left of T605 is not loaded so doesn't emit sound?

[R_J]

Re: Sony PVM 2730QM - Power Supply

If you reinstall only R677 is there still the cricket sound?
Then remove R677 and only install D654, Is there still the cricket sound?
With D654 removed, what voltage do you have on C654?

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

If you reinstall only R677 is there still the cricket sound?

No

With D654 removed, what voltage do you have on C654?

0.14V

Then remove R677 and only install D654, Is there still the cricket sound?

There is a buzzing sound, but not from D654.

[R_J]

Re: Sony PVM 2730QM - Power Supply

With D654 removed, do you have +140 volts and is there any voltage on D661 and also R654

[CapLeaker]

Re: Sony PVM 2730QM - Power Supply

Where did you have your probes located when you did your test?
This is not making sense to me.

[sunomo1]

Re: Sony PVM 2730QM - Power Supply

Where did you have your probes located when you did your test?

With D654 removed, do you have +140 volts and is there any voltage on D661 and also R654

With R677 and PS654 installed but D654 removed:
on C654 I have 9mV
on D661 I have 0.28V and about 12V to the ground
on R654 I have 0V and about round 12V to the ground
on 140V live I have 0.3V
on 15V live I have 11.5V
on 8V live I have 0.01V

[R_J]

Re: Sony PVM 2730QM - Power Supply

This makes no sense.

on D661 I have 0.28V and about 12V to the ground
on R654 I have 0V and about round 12V to the ground

Where are you measuring these voltages? on which side of the component? You list two voltages, is one reading on one side and one the other side, or the voltage changing?
Where is the12 volts coming from? with D654 removed and 0 volts on the 140 volt line, how can you have 12 volts anywhere?
If you have 12 volts on D661 and 0 on C654, then R652 is open or there is a break in the circuit somewhere
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With D654 removed You now have 0 volts on the 140 volt line. This tells me that without D654, the power supply is not working due to 0 volts on C654 which supplies ic651. This makes sense.
So D654 MUST be supplying 15 volts for C654 for the power supply 140 volt line to work.
If the transformer is good and you have no 8 volts, replace R677, D656 C659 and C655 because that are the only components on that line.
Try removing C659, maybe it is leaky.(you can try the supply witout it in circuit)

[CapLeaker]

Re: Sony PVM 2730QM - Power Supply

Something is off here. Earlier there were 130V on that 140V line.

[R_J]

Re: Sony PVM 2730QM - Power Supply

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

I don't know what's going on either, in post one, all the voltages were there, just a bit unstable

8V line 10.5V (not stable),

It looks like you may need to have the power supply FA-7 plug connected to the restof the monitor to turn on S/B line. which seems to turn off Q652 and turns on Q651
That 8v volt line is actually a +12 volt source line.