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The PVM-2730QM thread (H-STAT issue, colour bleed, convergence and more!)


buttersoft

Question

This thread started about a single issue, but is devolving into a more general thread about PVM-2730's, so I changed the title. These are basically the same as the KX27HG1 and KX27HG2 sets (powersupplies are swappable but may not be identical) along with the Japanese Profeel sets that look the same. They are close cousins of the US PVM-2530's and possibly the PVM-2550's. Different revisions have S-Video, and the US versions have a DB25 plug instead of SCART. The Japanese sets may use JP21. The service manual for the 2530 shows it to be a bit different inside, with a ton of tiny extra circuit boards and different layout. Still a lot of commonalities though, but it will pay to note these differences and check the schematics before touching anything.

 

Hi all,

 

I have a KX27HG1 (same thing as a PVM-2730) with a CRT fault. It powers up when cold, and then after twenty minutes, or even longer if it's freezing in the garage, there's a click (normally) and the screen shuts down. The picture folds in like the screen has been powered down, but the rest of the set still works - indicator lights, sound, etc. If I power-cycle, the tube powers up again for maybe a second, and then goes down. If I wait 10-20 seconds and power up again, the picture comes up for a few seconds, but the colours are bleeding sideways, particularly red. Then the CRT loses power again.

 

There's definitely a buzzing sound the whole time the picture is up, and it's not as stable as it should be at 240p, and the brightness flickers slightly. There's a click sometimes as it powers down that might be coming from the HVT/flyback, or might be something nearby.

 

Also, the "Screen" adjustment, on the neckboard of this set, doesn't seem to do a lot, mostly just messes with colour gain, but no huge brightness adjust or retrace lines appearing.

 

I just recapped the electroyltics in the power supply, and the same thing still happens. Any ideas where to go next? I've found replacement flybacks online, I think, but I'm not 100% on that being the problem.

 

Help greatly appreciated!

Edited by buttersoft
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Hello buttersoft, thanks a lot, some GND inside pictures maybe could help if something is missing on mine, the first time i opened up i noticed some miss screws and a GND cable that should be conected to the metal PSU plate was disconected, if im lucky and there is some cable GND missing, could be a good chance to try and test if solve the problem.

Thanks a lot, there is no hurry.

Edited by Dhampird
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I don't suppose anyone has found a source for those HV Blocks? The 2730qm I've just picked up has a jittering picture (randomly shrinking and expanding) which seems HV related.

 

I've not changed any caps on the PSU yet or even pulled it out to take a look but I'm fearing the worst

Edited by RetroRepair
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I don't suppose anyone has found a source for those HV Blocks? The 2730qm I've just picked up has a jittering picture (randomly shrinking and expanding) which seems HV related.

 

I've not changed any caps on the PSU yet or even pulled it out to take a look but I'm fearing the worst.

 

It could be HV related, but might just be dirty connectors somewhere in the set.

 

As the HV drops the image size will increase, higher voltage will result in smaller image.

 

Id expect some squealing or arcing if that HV block is faulty, there is a heap of capacitors in them that cause internal arcing if they fail.

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Yeah no signs of arcing or anything, gives me a little hope then!

 

Kinda hoping I find a dry joint or something when I pull the PSU and flyback but not holding my breath.

 

It does seem to be worse the brighter the image but I imagine this is just because the voltage is higher.

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Run the set in the dark with the back off, and see if there's any corona. There might be arcing you can't see in the light, though it's probably not that.

 

Do you know the H-Stat is faulty? If you suspect it but you're not sure, next would be to turn the set off and discharge, then remove the anode cap and H-Stat. When you've done that, take the anode lead and - gently - see if it moves in the socket. It should not do so, and you're not trying to break it here. But if it's already loose you're in trouble.

 

If the lead seems sound, reinstall the H-Stat and then ground your discharge lead to the frame, and wave the other end around and under the H-Stat while the set is running. If you're not getting any result, and you probably won't if there's no catastrophic failure, measure the voltage of the small leads coming out the back. Two of them are grounded, and two are for the HV regulation/feedback. You should be getting a stable voltage between the latter two - mine was about 4.66V on a working unit, and it doesn't change while the set is running.

 

I would guess that if these factors are accounted for, and if the pot on the H-Stat is working for static horizontal convergence like it's meant to, that the H-Stat is fine.

 

@RetroRepair were you the guy posting on the crt facebook group, btw?

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Yeah no signs of arcing or anything, gives me a little hope then!

 

Kinda hoping I find a dry joint or something when I pull the PSU and flyback but not holding my breath.

 

It does seem to be worse the brighter the image but I imagine this is just because the voltage is higher.

 

Generally speaking, if the power supply is struggling with a bright screen, the image size will increase as things get brighter.

 

The reason the image size increases with a lowered HV is because as drive voltage drops, the beam is easier deflected by the yoke, hence, the same amount of deflection force by the yoke bends the beam more so than if it is a higher voltage.

 

Make sense?

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Ok so theres some things there for me to look at, I'll try and do that in the next few days. If the H-STAT voltage on those terminals is not steady though could that not just be that the feed to it is also not steady?

 

Yeah that was my post on the FB group, it's a beautiful set and I'm totally in love with it, I just fear one day whatever component is causing the issue will fail and take a load of others with it!

 

Thanks for the explaination Neo Geo Man, I'm going to look more closely at the power supply section. It's not easy to do any testing on this while it's plugged in though. Might just be worth throwing parts at it until the issues goes away!

 

I did think bright screens made it worse but it doesn't seem to matter. Sometimes it's worse than others but now and then it's hardly noticeable. When it is though it's very noticeable!

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Ok so theres some things there for me to look at, I'll try and do that in the next few days. If the H-STAT voltage on those terminals is not steady though could that not just be that the feed to it is also not steady?

 

Yeah that was my post on the FB group, it's a beautiful set and I'm totally in love with it, I just fear one day whatever component is causing the issue will fail and take a load of others with it!

 

Thanks for the explaination Neo Geo Man, I'm going to look more closely at the power supply section. It's not easy to do any testing on this while it's plugged in though. Might just be worth throwing parts at it until the issues goes away!

 

I did think bright screens made it worse but it doesn't seem to matter. Sometimes it's worse than others but now and then it's hardly noticeable. When it is though it's very noticeable!

 

Sorry mate im in hospital on significant amounts of pain relief at the moment and struggling to read it all, but i dont think the issue is your power supply.

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If the H-STAT voltage on those terminals is not steady though could that not just be that the feed to it is also not steady?

 

Yes, but the HV change would have to be pretty huge to produce much difference on the leads. The H-Stat divider is significant enough that if it's not arcing I doubt it's causing the problem you're seeing with size changes, but it'd be better to rule it out. Display a static image and see what happens to the voltage between the leads over 60 seconds or so, once the set has warmed up for about that long first. If the voltage between them is moving, but the set is still on, come back in ten minutes and go again. The easiest place to measure is near the bottom of the solder side of the main D board, where the leads run to - remembering that's there's a few KV points on that board, so hands off! Keep the meter on stuff you know is safe, like those two leads :)

 

EDIT: If the reading between them is stable, there's no reason to connect them to ground at all. Doing so might stress the network behind them, which I'm guessing is where your issue is. Not that i have any idea what to do next :(

Edited by buttersoft
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Picked up 2 x PVM-2730QM's yesterday. Still in the car as they are 52KG ea and need to finish building a dolly and then get my neighbour to help lift them out. Then test them :D

 

Also got a BVM-2000AP (1987 model) which I got for nothing and has a few issues but what a monster at 50KG's!

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Picked up 2 x PVM-2730QM's yesterday. Still in the car as they are 52KG ea and need to finish building a dolly and then get my neighbour to help lift them out. Then test them :D

 

Also got a BVM-2000AP (1987 model) which I got for nothing and has a few issues but what a monster at 50KG's!

 

Thats a nice haul! Id come and help you lift them but im not meant to lift more than 2kgs for another week or so yet... If they came with remotes and power leads i can carry those inside for ya ;)

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Thats a nice haul! Id come and help you lift them but im not meant to lift more than 2kgs for another week or so yet... If they came with remotes and power leads i can carry those inside for ya ;)

 

Thanks for the non-offer :lol

 

I might have got the BVM for nothing but I think I’ll be spending some money on a physio

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I'm guessing buttersoft is busy this fine Saturday. I've just bought a -23 HVR for the PVM-2730QM as I didn't want it to go elsewhere at this stage. So either buttersoft will need it or I might need one in the future for my 2 2730's that I haven't yet had a chance to put through proper testing and tweaking. Either way, we have one if needed :D
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I'm guessing buttersoft is busy this fine Saturday. I've just bought a -23 HVR for the PVM-2730QM as I didn't want it to go elsewhere at this stage. So either buttersoft will need it or I might need one in the future for my 2 2730's that I haven't yet had a chance to put through proper testing and tweaking. Either way, we have one if needed :D

 

Busy on a free PVM pickup :) Sadly it looks like they're thrashed, bad burn-in, but the price was right.

 

Sony part No.s 1-230-712-21 or 22 or better still 23 will do.

Yup yup, it's suitable alright. I'm happy to buy it from you, unless you need it of course, just let me know. If you do use it, be f-ing careful not to twist the white lead already in place against the housing - i ripped the one i got apart, unless it was sold that way, or more likely unless customs had a good go at it :(

 

GJ WD that man, btw :)

 

EDIT: I sent the seller a msg to see if they have any more, cos you never know :)

Edited by buttersoft
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Oh, and the HVR's in general were expected to come pre-cooked about one in five times, according to the former agents i hit up before. They were real garbage, apparently. Hopefully this one is in good nick, but without applying HV you can't know.
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I also asked him if he had anything else for PVM / BVM when I also checked if he’d mind sending to you if I bought it so we didn’t miss out but he never responded to that but was OK to send to you if needed. i was going to ask again but got busy with the kids.

 

Anyway, when I get some time this weekend I’ll test my 2nd 2730 again as I know it has issues and the 1st one seems OK. Then we can work out who needs it,

 

Did you end uo getting your one from O/S working OK after gluing it up?

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Yeah, it works, but its readings are off compared to one i didn't fix, and the set has other problems now as well. I don't think they're being caused by the H-stat, but if you don't need it I'm happy to buy it. I have a spare flyback too, if you need one of those :)

EDIT: let me clarify, i have a flyback i bought against future need, not quite one i'm looking to get rid of.

Edited by buttersoft
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I checked my 2nd pvm and seems ok except for bad geometry issues I think so I shouldn’t need it.

 

If you pm me your address I will pass it on to the seller and I can send you his bank details if that works for you.

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So, an update. A second PVM-2730 has started showing the same symptoms - colours bleeding to the right, particularly red. Gets worse as the brightness is turned up. And the whole screen has a yellow cast to it. This second set isn't as bad, it's still very useable, once you get used to the overall slight discolouration.

 

I've narrowed the problem down to the neckboard with a pretty high degree of certainty. I have a third, completely working unit, and i swapped the neckboard from that one into one of the problem sets - bingo, no more problem. Next step has been to pin down the difference between the working neckboard and the faulty one - they're identical in terms of parts and layout, so far as i've found, but obviously something has gone out of spec. It's not the electrolytics, i've swapped all of those on the faulty board and nothing happened. And last night I changed out the four transistors in the red video sequence to no effect. I've also metered every component in the red signal path, and all appear to be in-spec/identical.

 

[ATTACH=CONFIG]136532[/ATTACH]

Neckboard schematic. Please ignore the red arrow, that was from earlier.

 

So, does anyone have any ideas? Is it possible for a diode or inductor else to fail partially, to test normal on a meter but then act like it has a short or otherwise? It is possible this problem is off the red signal path and part of the current limit? I did try replacing the v-blank transistors but I think I got the wrong ones and everything went blue, so I swapped the original ones back in.

 

@NEO-GEO Man, @Johns-Arcade, @Jomac any advice greatly appreciated :)

 

EDIT: possible blue signal problem vs ik feedback turning the picture yellow?

PVM-2730 neckboard schematic.png

Edited by buttersoft
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And the details are...

 

I’d been thinking about the red bleed problem again, and, having tapped out the red line and verified each component, in particular about the overall yellow cast to the screen and the need to turn the brightness down. I decided to test the sub-brightness control on the 12V rail next as this didn’t seem to be doing much. @soyl’s post saying to look at the socket got me thinking I’d take a look at the master brightness/screen grids first, as the only things connecting to the socket are the colour inputs, the heater, and then the divider network for the screen grids. The controls for these are handled on the neckboard, and are not on the flyback as is usually the case. Sure enough R702, in the red rectangle, first in line from the G2 input to the neckboard, was well out of spec. Was the first one I tested last night, which threw me off slightly. Not having a replacement, I swapped the in-spec one from the working neckboard, and problem solved. At goddamn last :)

 

PVM-2730 red bleed resistor.jpg

PVM-2730 neckboard.PNG

R702 in red

Socket resistor in green

 

Interestingly, soyl’s post made me look at the socket in more detail as I’ve been connecting and disconnecting to it far too much. It turns out there’s an unnumbered, unlisted resistor that’s a part of the socket itself, in the green circle, actually 100k, not 100R. You’d have to break the socket into pieces to get to it, but thankfully I didn’t need to. Soyl, I presume you’ve seen a few of those fail? Only Sony, hey.

 

@NEO-GEO Man, looks like your original idea with the cap on the grid rail wasn’t too far off. I should have followed that up with the brightness section :) Cheers to Johns-Arcade too, and to Homepin for being Homepin of course. And Claude for sorting me out with those spare H-Stat’s. I have a spare flyback too, along with some chroma IC's, and am now looking forward to many years of trouble-free operation :) This is, assuming i can replace the solid-carbon resistors with something else and not have frequency-response issues.

 

I have to dig out the second set with the fault as it’s in a driving setup backed into a corner, but when I do I’ll report whether the problem is the same.

 

EDIT: Yep, same problem :)

Edited by buttersoft
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