Author Topic: Revive dead Sony PVM-2130QM (Read 4277 times)

crt_cowboy · « **on:** July 28, 2023, 06:41:40 am »

Hello!

I have a dead Sony PVM-2130QM. I say dead because it doesn't power on any more.

The service manual is available here: https://archive.org/details/sony_PVM-2130QM_Service_Manual

First thing I checked was the power supply. No blown fuse. The 135v line was not giving anything. Tracing this line, I found that PS651(which is like a small fuse) failed open. After replacement, I got correct output voltages on this line.

Then I put it back and try to turn on the monitor. It made a noise like "plop" with a spark near the neck board (sparkgap?). Then nothing. PS651 blown again.

The fuse on the deflection board (D board) did not blow. Visual inspection there is no burned component or bursted capacitors. Tested the HOT and it is not shorted.

How can I further troubleshoot without blowing PS651 again ? Where should I look next ?

Swake · « **Reply #1 on:** July 28, 2023, 08:53:35 pm »

Have no experience with CRT repair but would look in the vicinity of that 'pyrotechnics' event. Would also check if the tube is still in good condition.
The flyback transformer named T604 (page 39; location D13) might need a checkup too.

fzabkar · « **Reply #2 on:** July 28, 2023, 11:14:35 pm »

Aside from the FBT, I would check the damper diodes and tuning capacitors. Also check for a short on the 200V and 24V secondary outputs. You could also disconnect the HCT transformer for testing purposes.

Do you have an FBT ring tester? If not, you could inject a sinusoid into one winding and look for ringing on another winding with your CRO. I used to use the capacitance test function of a DMM to provide the sinusoidal input.

A possible worst case scenario is a cracked CRT (if you see arcing at the electron gun).

crt_cowboy · « **Reply #3 on:** July 29, 2023, 05:23:50 am »

Thanks for the suggestions! Nice tip to check them without ring tester.
I swapped the FBT with a spare one but it didn't solve the issues. I also checked diodes on the D board.
Will further check for short. What do you mean by "remove the HCT transformer"? Remove the FBT, T552 or T553

fzabkar · « **Reply #4 on:** July 29, 2023, 05:16:28 pm »

HCT = T553 = Horizontal Centring Transformer?

crt_cowboy · « **Reply #5 on:** July 30, 2023, 05:46:52 am »

Thanks so I removed T553 as suggested. I still get the same thing: a spark in the neck board area and the power supply small internal fuse that blow up. Really strange...

fzabkar · « **Reply #6 on:** July 30, 2023, 05:54:27 am »

Remove the neck PCB and see what happens?

crt_cowboy · « **Reply #7 on:** July 30, 2023, 06:25:51 am »

With the PCB neck disconnected, it doesn't blow up. I can hear the crackling noise in the tube (high voltage present.
Does it mean there is a short in the tube?

fzabkar · « **Reply #8 on:** July 30, 2023, 06:47:29 am »

Could the noise be coming from the yoke arcing to the aquadag coating? Or is it coming from the CRT anode? Is it a different noise?

Do you have a high voltage probe to measure the EHT?

Are you sure there is no air in the CRT?

crt_cowboy · « **Reply #9 on:** July 30, 2023, 06:57:26 am »

For me this is the "normal" noise a tube like this is doing when you turn the monitor on.
I will see if I find a HV probe.

crt_cowboy · « **Reply #10 on:** July 30, 2023, 06:59:23 am »

The tube still looks sealed. I didn't find any cracks of indication there is air inside.
I had once a tube with air and this was making a noise very recognizable when turned on.

fzabkar · « **Reply #11 on:** July 30, 2023, 07:16:18 am »

Sometimes a CRT can develop a heater-to-cathode short. However, I think your TV has a floating heater winding on the FBT, so this would rule that out.

You could measure the voltages at the neck PCB to confirm that they are within spec.

If you have a high impedance CRT probe, you could measure the pulse amplitude at the collector of the horizontal output transistor. An open tuning capacitor can cause this pulse to go high.

crt_cowboy · « **Reply #12 on:** July 30, 2023, 07:58:37 am »

At the anode cap I get 28KV.
Trying to measure G1 and G2 voltage at the neck PCB (unplugged from the tube), I don't get something stable. Only a couple of volts.

fzabkar · « **Reply #13 on:** July 30, 2023, 08:35:35 am »

I would normally expect to see an EHT of 25kV. Perhaps 28kV is OK for your model??

From memory, typical voltages for G1 and G2 would be around 400V or higher for G2 and around 160V for G1 (when screen is dark). I'm referring to colour CRTs in general, not necessarily yours.

Maybe there is a short in the gun:

https://www.repairfaq.org/samnew/tvfaq/tvdoefosv.htm

See the "High Voltage Power Supply Problems" category:

https://www.repairfaq.org/samnew/tvfaq.htm

fzabkar · « **Reply #14 on:** July 30, 2023, 09:05:45 am »

I had a look at the circuit diagram and ITSM that G1 should be about 30V (= 82K/552K x 200V). The cathodes are sitting at around 150V - 160V. Sorry, my memory led me astray.

crt_cowboy · « **Reply #15 on:** July 30, 2023, 09:13:06 am »

I will try to understand why there is no G1 or G2 voltage.
For the tube, I will see if I can get a CRT tube tester working on this tube. I have a Muter BMR device but not the right adapter. Might need to wire it myself.

crt_cowboy · « **Reply #16 on:** July 30, 2023, 01:49:17 pm »

Further troubleshooting with the neck board disconnected.
Made some measurements on the FBT:
Pin 4 (should be 200v) measured 136v
Pin 5 (should be 135v) measured 136v
Pin 10 (should be 24v) measured 0v

Uunoctium · « **Reply #17 on:** July 30, 2023, 02:31:54 pm »

Sony has never moved away from its CRT internal horizontal convergence, abbr. HV-stat. Early models had an coaxial HV connector(!) and the wellknown 'red block'. Later on they implemented one resistor, part of an voltage divider, right into CRT!
The other part is the 110Meg pot (RV702) on CRT plate.
Acc to an engineering bulletin some uncontrolled sparcs can occur around CRT socket or board. Recommended solution was to replace complete CRT board.
Blown fuses in combinantion with this issue are rather unknown.

(And yes, i've also seen sparkling along the internal resistor 1 or 2 times. CRT dead)

crt_cowboy · « **Reply #18 on:** July 30, 2023, 03:16:01 pm »

Thanks I hope the tube itself is not bad.
For now I am digging more on the deflection board and the voltages from the FBT.

Uunoctium · « **Reply #19 on:** July 30, 2023, 04:19:47 pm »

24V missing?
Seems to be the power source for vertical output stage. Check diode, electrolytic capacitor and final out IC*.
And do'nt run unit without vertical deflection! CRT burn in is guaranteed in much less time, as you expect.

* Very common failure in many consumer TVsets.

fzabkar · « **Reply #20 on:** July 30, 2023, 06:01:26 pm »

Quote from: crt_cowboy on July 30, 2023, 01:49:17 pm

Further troubleshooting with the neck board disconnected.
Made some measurements on the FBT:
Pin 4 (should be 200v) measured 136v
Pin 5 (should be 135v) measured 136v
Pin 10 (should be 24v) measured 0v

It sounds like the HOT is not running, in which case 1000V should also be missing. Perhaps it needs the CRT PCB to be connected?

crt_cowboy · « **Reply #21 on:** July 30, 2023, 06:17:55 pm »

Yes the 1000v is also missing.
The problem is that with the CRT PCB connected the power supply internal fuse blows...

fzabkar · « **Reply #22 on:** July 30, 2023, 06:26:25 pm »

It looks like there is some interlock or protection mechanism that is preventing us from running the TV without the neck PCB attached to the gun. Bugger.

crt_cowboy · « **Reply #23 on:** July 30, 2023, 06:53:12 pm »

Yes I will see if the CRT tube tester detects a short or an issue with the tube.

crt_cowboy · « **Reply #24 on:** July 31, 2023, 04:58:43 am »

Ok so as there is no right CRT adapter on my tester. I plan to map the wires as follows:
Adapter > CRT Neck
Kg > pin 10 (KG)
Kr > pin 12 (KR)
Kb > pin 11 (KB)
G1 > pin 6 (G1)
G2 > pin 5 (G2)
G3 > pin 3 (G4)
H > pin 7 (H1)
24 > pin 8 (H2)

Looking at the diagram H and 24 should give 11v for heathers. I measured 10v from the FBT so I guess it is OK.
My CRT regenaror has G3 not G4. I guess it is fine to connect the G3 to my tube G4 ?


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