PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC? IC?

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deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: pvm-20m2u vertical shake/roll after recap

Post by deezdrama »

So I still have the vertical rolling issue, I couldnt remember if I tried swapping out the input signal board so put the one in from my 14m2u.... Same issue but noticed the rolling was way slower.

Went in and adjusted the vhold from the menu and was able to stop the v rolling!
I tried this before with the original input board but it would not stop the rolling.

I still have a vertical shaking which ive seen and fixed before with new caps but ive already replaced all the caps in the deflection circuits.

https://youtube.com/shorts/E0V1uV9gBVE?feature=share


One of the vertical output transistors feels super hot compared to the other.
Actually I felt heatsinks of all the H and V transistors and they all are just semi warm/hot but that one V output transistor i can only touch for about 2 seconds before it burns my finger.

Used a cheap temp gun which isnt very accurate but most of the heatsinks read 20-30c while the hot feeling V out transistor read 40-55c

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It still seems to me like a bad cap but ive never had a crt with a bad or failing H or V out transistor so not sure if they just typically fail or can begin to go bad causing a vertical jitter/unstableness like this.

Anyone have a vertical or horizontal ic start to go bad and cause issues like this?

I need to really get a scope and learn to pinpoint an issue but at this point thinking about ordering new vertical transistors and check vertical caps again when i pull the board to replace the V transistors.

Probably wasting time and money but its all a learning experience i guess untill I can afford a rigol scope.
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: pvm-20m2u vertical shake/roll after recap

Post by deezdrama »

Well I took a break from the 20m2u and worked on the 14m2u that ive been stealing parts from.
Got it up and running fine and noticed its vertical ic's are just as hot so I dont think thats the issue with the 20m2u...


Back to the 20m2u, i stayed home today and spent (wasted) the whole day on this 20m2u...


Swapped rear input board ..... Same issue but now vhold would stopthe vertical rolling but image still horizontally stretched a bit like bad pin amp adjustment and image was still vertically jumping all around.


Probed voltages coming into chassis.... All seemed good. 15v was spot on, 115v spot on, -15v is like -25v which is weird, 5v is 4.8v which im not sure if thats within spec or not.


Spent entire day looking over board with magnifying lense.... Checked all caps with 2 esr meters.

Found sync seperator ic pinout in serv manual.... Live probed each pin.... Voltages look good.

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Reflowed ENTIRE deflection half of the board, every damn tiny surface component and everything...... Still has same issue.

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Checked that all resistors on deflection side werent failed open. Checked all diodes for typical diode voltage drop.


Studied serv manual looking for clues.... Seen ic107 and that it controls vhold and other vertical functions....
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Found it on the board opposite of the deflection side..... It had a few electrolytic caps nearby that tested high esr..... Replaced those caps..... Same damn problem with stretched image like the pin amp is off and vertically jumping.
After the initial recap and repair the geometry and image were spot on. It wasnt untill the pvm ran for 30min that a cap or something failed over a minute or two timeframe which is why I think its a cap.....

I just wish I knew where to look, im sure its a simple fix.
Grasping for straws..... Anyone have some straws? Lol
tongshadow
Posts: 613
Joined: Sat Jan 07, 2017 5:11 pm

Re: pvm-20m2u vertical shake / rolling after recap of deflec

Post by tongshadow »

It's a shame the M series isnt modular like the L4/L5 and BVMs, would've made diagnosis far easier by just swaping boards.
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: pvm-20m2u vertical shake / rolling after recap of deflec

Post by deezdrama »

tongshadow wrote:It's a shame the M series isnt modular like the L4/L5 and BVMs, would've made diagnosis far easier by just swaping boards.
Yeah, i wish i could find a loose chassis board at this point.

Good thing is i have a working 14m2u and so if i get a scope i can cross reference some things i guess
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by deezdrama »

Ended up getting a scope. Its an entry level siglent....what you would probably consider the cheapest real scope you can get thats not a toy but should be fine for me to compare signals on board with waveforms in the service manual.
I built a little signal generator and my scope knowledge is pretty low but got the probes compensated and at least can use auto to see any signal im probing.
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I just spent a couple hours painstakingly piecing together the horrible block diagram and schematic sections all nastily cut up in segments in the pvm 20m2u service manual..... Crap I hated jumping up and down page to page, zooming out and back in, trying to find the path you last looked at between pages of butchered schematics.

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Anyway.... Starting to feel like im in over my head. So much time and money wasted on this monitor. I have a scope now but not even sure where to look for the problem. Im eager to learn this stuff but at times it feels overwhelming and makes me feel like I should of just shotgunned the vertical circuit from output on the chassis board and work my way back untill it worked.... servicing these is like a lost art that not many know or sit behind paywalls for those wanting help :(
tongshadow
Posts: 613
Joined: Sat Jan 07, 2017 5:11 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by tongshadow »

You might be close... I would analyze the waveforms related to the vertical circuit, thankfully the service manual is kind enough to provide them.
jd213
Posts: 412
Joined: Mon Feb 01, 2016 9:03 am
Location: Pennsylvania

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by jd213 »

You used the updated cap list that's originally from Savon Pat, right? That has a couple caps that exceed the factory values.
If you haven't bought a kit from him, maybe buy one and then see if he can help you out over the phone (I've heard he doesn't like long emails).

Thankfully he isn't using Chinese caps any more as was reported on Reddit and some arcade forums years ago, I recently got an L5 kit from him and it's mostly Nichicon caps with a few Rubycon ones.
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by deezdrama »

tongshadow wrote:You might be close... I would analyze the waveforms related to the vertical circuit, thankfully the service manual is kind enough to provide them.
Sitting here right now with scope on.. Trying to build confidence :lol:
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by deezdrama »

jd213 wrote:You used the updated cap list that's originally from Savon Pat, right? That has a couple caps that exceed the factory values.
If you haven't bought a kit from him, maybe buy one and then see if he can help you out over the phone (I've heard he doesn't like long emails).

Thankfully he isn't using Chinese caps any more as was reported on Reddit and some arcade forums years ago, I recently got an L5 kit from him and it's mostly Nichicon caps with a few Rubycon ones.
Yup, I used the updated spec caps per the sony bulletin/savon pats kit.

I had a 14m2u and this 20m2u, both got the same identical cap kit I put together from mouser using 105c nichicons.

The 14m2u works great now with same caps...

This 20m2u worked great right after recap for 30min untill something went bad.


Good idea on buying a pat kit. Might be price of admission for live tech help lol... I just would hate to spend $40 for nothing but might do this as a last resort.

Heres the 14m2u with same caps...
https://youtu.be/43_7_rWHju8
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by deezdrama »

Well, pulled the board for the umpteenth time, used my new nerd 3.5x magnified visor to double check all polarity of caps I installed, checked esr, looked for cracked solder joints...... This is probably the 4th time ive done this and whole deflection half of the board has been reflowed.

Looked for waveform points to check in the deflection schematic and that sync IC chip that ive already replaced seems like last spot to check waveforms against the ones in the service manual before signal goes to V drive, and Voutput transistors.


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Im a total oscilloscope noob but to my untrained eyes all the waveforms looked good.
Bought the scope to help troubleshoot this monitor but im just more confused than ever and discouraged.
Starting to feel insane with all the time ive scratched my head over this.

No clue what it could be or what to check at this point.

Thought maybe a bad cap in power supply board but I tested another board before and the issue didnt change.
Wondering if vertical out transistors could partially fail like this.

Probably something stupid simple but out of ideas how to find it.

EDIT.... Found some weird signal spike
https://youtu.be/7fuTLJ6yqhc
tongshadow
Posts: 613
Joined: Sat Jan 07, 2017 5:11 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by tongshadow »

Forgot to mention, but you can try contacting savonpat on ebay. Many people had success solving their issues this way.
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by deezdrama »

tongshadow wrote:Forgot to mention, but you can try contacting savonpat on ebay. Many people had success solving their issues this way.
I tried that but got no response.

Hopefully getting close to the cause

https://youtu.be/eKvYDx0n22M
deezdrama
Posts: 203
Joined: Sat Dec 21, 2019 4:10 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by deezdrama »

Well, time to resurrect this thread.

Seen a 20m2u on ebay with a bad tube, messaged the seller and asked if I won if we could bypass the crazy shipping prices and just ship me the boards. He agreed and I was the only bidder.....here we are.

Was excited to try the chassis board out in hopes to have a fully working 20m2u but noticed he recapped the board with chongx caps :(

so looks like I need to recap one of these boards yet again :( :( :(

He showed images on his ebay listing of the pvm working but green gun was out.... so I know he ran it with the ching chong caps.... should I dare test with them installed .... :|

Image
tongshadow
Posts: 613
Joined: Sat Jan 07, 2017 5:11 pm

Re: PVM-20M2U Vertical shake -Sync? Vhold? Oscillator? AFC?

Post by tongshadow »

Chong caps are bad indeed, but I would only worry in the long run. They probably test fine and I doubt a bad cap could take out a gun without some sort of protection triggering first.
It's also a good idea to test as is, in case it doesnt work and the seller blames you for changing the capacitors.
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