Revive dead Sony PVM-2130QM - Page 1
Forum section: electronics / repair

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 28, 2023, 06:41:40 am
content: 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_ManualFirst 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 ?

author: Swake
author_rank: Frequent Contributor
timestamp: July 28, 2023, 08:53:35 pm
content: 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.

author: fzabkar
author_rank: Super Contributor
timestamp: July 28, 2023, 11:14:35 pm
content: 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).

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 29, 2023, 05:23:50 am
content: 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

author: fzabkar
author_rank: Super Contributor
timestamp: July 29, 2023, 05:16:28 pm
content: HCT = T553 = Horizontal Centring Transformer?

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 05:46:52 am
content: 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...

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 05:54:27 am
content: Remove the neck PCB and see what happens?

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 06:25:51 am
content: 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?

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 06:47:29 am
content: 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?

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 06:57:26 am
content: 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.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 06:59:23 am
content: 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.

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 07:16:18 am
content: 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.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 07:58:37 am
content: 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.

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 08:35:35 am
content: 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.htmSee the "High Voltage Power Supply Problems" category:https://www.repairfaq.org/samnew/tvfaq.htm

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 09:05:45 am
content: 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.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 09:13:06 am
content: 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.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 01:49:17 pm
content: Further troubleshooting with the neck board disconnected.Made some measurements on the FBT:Pin 4 (should be 200v) measured 136vPin 5 (should be 135v) measured 136vPin 10 (should be 24v) measured 0v

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 30, 2023, 02:31:54 pm
content: 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)

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 03:16:01 pm
content: 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.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 30, 2023, 04:19:47 pm
content: 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.

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 06:01:26 pm
content: Quote from: crt_cowboy on July 30, 2023, 01:49:17 pmIt sounds like the HOT is not running, in which case 1000V should also be missing. Perhaps it needs the CRT PCB to be connected?

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 06:17:55 pm
content: Yes the 1000v is also missing.The problem is that with the CRT PCB connected the power supply internal fuse blows...

author: fzabkar
author_rank: Super Contributor
timestamp: July 30, 2023, 06:26:25 pm
content: 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.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 30, 2023, 06:53:12 pm
content: Yes I will see if the CRT tube tester detects a short or an issue with the tube.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: July 31, 2023, 04:58:43 am
content: Ok so as there is no right CRT adapter on my tester. I plan to map the wires as follows:Adapter > CRT NeckKg > 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 ?

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 04, 2023, 07:45:41 am
content: Ok so according to the tube tester, there is no short in the tube. The tube itself measures very good for emissionsIt means the issue is probably around the deflection board or neck board. I will dig further.An other idea would be to swap those boards with a good unit. But those PVMs are quite expensive I would prefer to avoid further damages.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 04, 2023, 01:22:00 pm
content: Here is a video of the issue:I have the impression the spark is inside the tube.

author: fzabkar
author_rank: Super Contributor
timestamp: August 05, 2023, 12:26:33 am
content: It's definitely sparking inside the tube, but is it because the input voltages are too high? I would check that all the CRT grounds are secure to ensure that the EHT is following the correct paths.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 05, 2023, 07:52:36 am
content: Ok I will check the CRT grounds.I am still wondering if the tube is good. The tester says it's good but it's not bullet proof.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 06, 2023, 04:15:03 am
content: Double checked and the grounds are all good.Not sure why the ETH doesn't follow the right path...I am wondering how I could check the rest of the voltages without blowing the power supply. Would a series lightbulb on the B+ line do the trick ?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 06, 2023, 04:50:54 pm
content: tl;drPlease check the whole H-Stat circuit on CRT board - right up to the contact in socket (CV, P 1).Why? If there is any open, no current draws across the CRT internal resistor and conductive joints in CRT neck charging up to HV

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 07, 2023, 05:40:20 am
content: Thanks I did check the h-stat section and did not find bad component.Will try to swap the full CRT board from a working unit.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 07, 2023, 07:11:33 am
content: Do you have access to HV insulation tester? With idling voltages around 1,5 ... 5 kV? For measuring a possible path from Anode to Grids (G2,G4 etc). Your CRT tester finds no faults, shorts and H-Stat seems also be ok. It looks, there are olny two possible pathways left.1. Andode has regular connestion to two accerlerating-grids in tube neck with G4 between. A short may lead G4 gets Anode voltage2. I remeber a rare fault at an consumer model (KV20xx early '80). Chassis had the coaxial HV connector and red block. H-stat did'nt work. Two independend repair facilities +Sony itself diagnosed CRT fault caused by inernal short. Got it for free and measured w insulation tester ~ 120MOhm. I could fix that.Regardless of coaxial or separate feeding the H-Stat plates, an possible short or unwanted resistance in your CRT between the two may cause the lightnings.In my humble opinion, the sound and visible spark are indicating a huge enrgy of some Joules. I argue that points close to an 24kV spillover.(Addendum:always discharge CRT before connecting anythig...)

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 07, 2023, 10:09:48 am
content: Thanks for the suggestions.I will still do the CRT Neck board swap to rule out h-stat issue.Unfortunately I don't have an isolation tester but if I get it right the two options you suggest would mean some problems with the tube itself.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 07, 2023, 11:24:14 am
content: In worst case - yes

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 07, 2023, 04:16:43 pm
content: If that's the case is there a way to remove those shorts?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 07, 2023, 07:39:13 pm
content: I do'nt think so. At my special case, it was great luck. Center conductor in the coaxial is H-Stat is connected via a spring. I separated/isolateted both with a piece of silicon hose and charged the large internal Anode capacitor of CRT with my insulation tester. Afterwards i shorted the accumulated charge through the unwanted resistor by connecting H-Stat to ground. It was necessary to repeat that three times. In other words, i burned the short away. Unit worked for more than 15 years without any trouble and finally i gave it away as gift.Be cautious with such experiments before you can clearly diagnose and measure such internal shorts.If not done already, check Ub (135V?) and paralleld capacitor to horizontal driver. Both having effect on picture width and(!) HV. PVM and BVM are normally equipped with two or three independent circuits to avoid improper HV and limiting CRT cathode over-current.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 08, 2023, 05:40:01 am
content: Yes B+ 135v voltage was checked.When measure HV at the anode I get 28kv. I don't know if that's the normal voltage.Which capacitor do you mean? C578 ?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 08, 2023, 11:32:53 am
content: I had a phone call with an retired engineer, who formerly worked as repair specialist in broadcast service. Mainly with Sony equipment. I extracted the video url and mailed to him, and his first reaction was: OMG, is that really happen inside tube? Immediate stop further try to power unit on, otherwise the tube will be damaged. If not done already.His thougt after looking at SM, that the HV in region of 28kV would be to high. Manual gives no hint about. Two protection path are in this chassis: ABL (BL = Beam Limit) and HV (Over)Voltage protection. Second is done via the divider network in HVR called block. He replaced some of them during his his long-standing years of practical service. Early ones are brown, the late version yellowish. Some went high impedance. I guess, resistance will be in regions of 10^2...10^3 MOhm.The second hint was to check both protection path. He remembers a fault in ABL, but the apperance of that failure was, that EHT was not coming up.He also mentioned PSU main Volatage 135(140)V - but we can exclude, cause it was checked by you and finding was ok.He not recommended to follow my suggestion first to measure possible internal tube shorts, before it is not clear, that EHT is correct.That was all, I could squeeze out of himAddendum: he warned also to power the unit, if unclear that H-stage runs in spec, to prevent a heater damage

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 08, 2023, 12:10:07 pm
content: Thanks I really appreciate the help. Will further investigate based on the recommendations

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 08, 2023, 12:47:02 pm
content: While the HV voltage control path remains, if Anode cap is removed, you can measure and compare signals in H-stage with diagrams in SM. So that should not affect its function. The cathode current control is only for over-current, so it also should not have an negative effect. PSU is galvanic isolated, so there is no danger by connecting an oscilloscope probe. Th first point, i would observe is base of Q552.I think, these measurement could be done, while CRT socket is removed (Heater protection)Earlier mentioned capacitor is split into three. C581, C586, C582. I would inspect them - in doubt measure capacitance, cause critical. C581 builds an capacitive divider w C587, so it should included in inspection. C583 is too large in relation to C582 - i guees its an filter capacitor. Not really necessary to do, but check it.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 09, 2023, 05:45:27 am
content: Thanks will give an update this weekend as I will be away a couple of days.Measurements without the anode cap should work but I think the CRT neck board must be connected. When not connected I did not get correct voltages which suggested the HOT was not running

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 14, 2023, 12:11:36 pm
content: Alright small update, one a good monitor I also get 28KV at the anode.I also checked the capacitors on the deflection board as suggested. Did not find anything bad.I will continue to investigate as suggested and report progress here.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 15, 2023, 08:44:14 am
content: I checked the deflection board and did not find issues.I swapped the deflection board, the CRT neck board, the HVR from a good unit.Same issue so I think it is fair to assume the issue is within the tube itself.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 15, 2023, 09:04:04 am
content: that doesn't really sound encouraging

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 15, 2023, 09:19:34 am
content: Worst case it will be a part donor.The last thing I can try is to use an isolation tester and see if I can remove the short ?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 15, 2023, 04:16:54 pm
content: I'm less optimistic to reserved about that. Depends where an possible short is located. Your tube is different consructed to mine, because I had direct access to HV electrodes. At your tube HV is only indirect accessible via a inside located high impedance resistance.We can rough calculate. On CRT Board an paralleled capacitor is rated at 6,3kV. Lets say, Sony stets HV-Stats operational point to 3kV and with RV702 = 110MOhm we get I = 27µA.28kV-3kV= 25kV/27µA = 916,6MOhm!Somewhat in that region should be measurable w insulation tester.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 15, 2023, 06:41:08 pm
content: Do you mean measuring resistance between pin 1 of CRT and anode (the internal resistance of the tube) ?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 15, 2023, 06:55:49 pm
content: Yes! This resistor is a thick-film one, printed on white ceramic. Sparkling at or over it isn't a new phenomenon. Saw it first at an SUN labelled workstation monitor, which internal build remebers at grade 1 broadcst chassis, like BVM 2010.Didn't know that such resistors were also used in consumer chassis.Here at a wide KV-C2121D(only German)https://www.repdata.de/wbb2/forum/index.php?thread/835-%C3%BCberschlag-in-bildr%C3%B6hrenhals-an-sony-tv/

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 15, 2023, 07:05:03 pm
content: Other possible pathes for crawling HV are G2 and G4, cause accelerating grids connected to Anode are between them.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 15, 2023, 07:59:53 pm
content: I will check and provide an update. Even if the chance it can be repaired are very thin I would like to confirm where is the fault.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 16, 2023, 09:17:25 am
content: I did some measurements with the isolation tester, look like the internal resistor of the tube failed open. Unfortunately there is no way to fix it.

author: crt_cowboy
author_rank: Regular Contributor
timestamp: August 18, 2023, 10:50:47 am
content: Just wondering are there some consumer TV with the same tube (A51JKQ10X) ?From what I found online GVM-2020 and PVM-1960 might work but both are very hard to find.Any other options?