Sony pvm 2053 very odd geometry & OSD issue (1953 / 20m2)

[phosphor]

Hi,

Apologies for barging straight in as a new member with a technical qundary but this forum seems to top the google results now for almost every PVM issue I have researched in the past, so I figured it was probably the best place to bounce a problem off and see if it resonates with anyone...

I have been fiddling with PVMs for a while now and have one which has had me banging my head against a wall for a while - its a 2053md (1953md for Americans - same monitor but lacks the closed caption card). Predecesor and same spec as 20m2mde, this one is 1995 YOM.

It has very severe pin cusion issues in its horizontal deflection, this is not altered with the service menu (and various adjustments in said menu do not appear to do much WRT horizontal adjustments).
The other clear oddity is that the OSD text is green, however when non RGB inputs are selected this has a haze of white around the text, almost like it is overlaying white with green.

(Apologies for rubbish photobucket images)





Now, I have had a good go at this - I have replaced most of the capacitors that are in any way involved in the deflection and pin-cusion areas of the circuit. I have tested anything seemingly relevent with my ESR meter (most caps are fine).

I have measured the voltage from the DAC to the pincusion parts.
I have given everything a good eyeball and shouting at.

Now, what is interesting is that the DAC on these monitors provides an active output, that is the voltage varies with (and in sync) with the vertical refresh - I was assuming that it would just be a bias / adjustment as it was replacing trim pots of the older 2043 series, but it looks like they pushed quite a few timing duties to the micro as well.

I was wondering if anyone had any experience with similar issues. I do suspect this could still be a cap, but not one in the deflection side - maybe a little DC blocking one somewhere in line with sync signals, meaning the micro is out of step with reality? I have scourered the service manuals block diagrams and schematics to death and tested everything I can but have got no further (I did replace a few iffy electrolytics in the deflection side en route, and have a better & sharper distorted picture, but still...)

Many thanks in advance, all tips welcome.

Will try and help out others with PVM issues, I have fiddled with quite an array now...

[buttersoft]

Yeah that looks like fun. About all i can do is use google and direct you to info about pincushion circuit failure - http://repairfaq.cis.upenn.edu/samnew/tvfaq/tvewpp.htm

From the service manual, maybe start with IC509 and the circuit around it, particularly Q503. Neither is easy to see on the schematic i have, but it's for a 1350, so the one for the PVM-20M2 might be better, if you can't find your exact model. Basically they're left and slightly down from the schematic representation of the deflection yoke.

This is a total guess at this stage, you already sound like you know more than i do, but you did post up I'd love to hear if you manage to diagnose it. Not sure about the green glow.

[MKL]

Assuming these schematics are of your monitor, start by checking the damper diodes D502 and D512, then the resonant capacitor C514 and if they're all good move to Q503. If the schematics don't match your monitor, find the corresponding components. East west correction is always done with a conventional diode modulator circuit like that.

https://i.imgur.com/4tw4aPI.jpg

[phosphor]

Hi buttersoft, thanks for the comments. I have given Sams FAQ a good read in the past - it does give good advise on this but it ends at the theoretical level - essentually that pincushion correction is where a half wave signal, synced to vertical deflection, is applied to offset the horizontal deflection to counter the fact that the tube is curved / non linear. It also points out that this is done in most cases (including this one) with a coupled inductor.

And IC509 which amplifies (or buffers) the output from the DAC (which produces this rectified AC looking waveform) seems OK (I scoped it). Pretty sure Q503 is alright, it passed a diode test on multimeter anyway. It is very hard to work on this set live as you cant get to much when its assembled, so you have to plan ahead with tag wires to probe with it running. All a bit sinister.

These sets make heavy use of signal transistors as switches, shunting in resistors to change timings and parts of the curcuit to account for video standards, 16:9, Overscan, Underscan modes etc, which makes analysing the circuit very painful...

Of course I will post back if I solve it, no worries

Yeah that looks like fun. About all i can do is use google and direct you to info about pincushion circuit failure - http://repairfaq.cis.upenn.edu/samnew/tvfaq/tvewpp.htm

From the service manual, maybe start with IC509 and the circuit around it, particularly Q503. Neither is easy to see on the schematic i have, but it's for a 1350, so the one for the PVM-20M2 might be better, if you can't find your exact model. Basically they're left and slightly down from the schematic representation of the deflection yoke.

This is a total guess at this stage, you already sound like you know more than i do, but you did post up I'd love to hear if you manage to diagnose it. Not sure about the green glow.

[phosphor]

Hi MKL,

Thanks, thats good advice - I have not looked too much at that part as its on the Horizontal drive output from the PC1377C chip - and the image on this is actually not too bad (just distorted) so I had focussed more on the pin-amp side of things...
Will give it a look this afternoon. C514 looks to be a 22nF 630v film cap on the schematic here, just after the main horizontal drive transistor?
(yes, that is the schamtic for this set btw -I had that exact page open when I saw your post too - uncanny!)

Assuming these schematics are of your monitor, start by checking the damper diodes D502 and D512, then the resonant capacitor C514 and if they're all good move to Q503. If the schematics don't match your monitor, find the corresponding components. East west correction is always done with a conventional diode modulator circuit like that.

https://i.imgur.com/4tw4aPI.jpg

[MKL]

I have not looked too much at that part as its on the Horizontal drive output from the PC1377C chip - and the image on this is actually not too bad (just distorted) so I had focussed more on the pin-amp side of things...

Where do you think the pincushion correction signal goes? It's injected into the horizontal deflection coil through the horizontal output circuit (the horizontal damper diode D506 which together with the EW diodes D502/D512 becomes conductive during the horizontal scanning period, i.e. when the horizontal output transistor Q501 is turned on. There's nothing special here, it's the same as any consumer TV, a 10 minute fix job for any TV tech that has never seen a PVM in his life.

Here I helped fix the same issue (I'm user M. N.). Different PVM but the same thing:

https://www.facebook.com/groups/4438761 ... 232833279/

[phosphor]

strangely, on your schmatic image the two damper diodes are marked "Pin Damper" - and on mine they are not (but the circuit is more or less the same) - https://imgur.com/a/hXYaDOC

For some reason I had convinced myself that the pin correction was done with the negative side of the yoke via T503 somehow as it seems to interface with this through L509 - with the positive side seeming to go to what I presume is the flyback primary winding mainly - but yeah I can see now that it is all mixed up together with the Damper circuit... I have not got anywhere near this involved with CRTs before - mainly just the PSUs and obvious repairs where a cap has visibly died, but this one feels tantilisingly close - when flippling sync configs on my source it sometimes widens the image for half a second...

Anyway, I have taken out and tested on an LCR meter C514 and C525 and they are both good / spot on with 0 dissipation factor.
D502 and D512 (which are both identical and in parallel ?) are both fine, 0.423v forward voltage. I also tested forward conduction of D506 and that was 0.454v (suspiciously low really as its a 1500v fast recovery diode, but then diode test on DMM is minescule compared to the 4A rating... )

The transistors all pass basic diode tests (are not open / shorted at least)?
I have also checked all electrolytics around this area, including power rail reservoirs (which seem to be sprinkled everywhere in this set...)
There is a 12v regulator (IC505) from a winding on the flyback and what looks like a transistor regulated supply from the main 15v rail via Q520 that interact in a strange way via D539 that I cant understand - but I feel like checking the operation of these supplies might be a good next step...?

Any other pointers - its all laid bare at the moment

Thanks again for you help!

Where do you think the pincushion correction signal goes? It's injected into the horizontal deflection coil through the horizontal output circuit (the horizontal damper diode D506 which together with the EW diodes D502/D512 becomes conductive during the horizontal scanning period, i.e. when the horizontal output transistor Q501 is turned on. There's nothing special here, it's the same as any consumer TV, a 10 minute fix job for any TV tech that has never seen a PVM in his life.

Here I helped fix the same issue (I'm user M. N.). Different PVM but the same thing:

https://www.facebook.com/groups/4438761 ... 232833279/

[MKL]

The EW circuit is supplied by 24V from the flyback (pin 5). There are safety (flame proof) resistors in series with this voltage (R535, R541, R1514) that could go open. The EW correction waveform is a parabola so if you have a scope check the output of the EW transistor and coil.

[phosphor]

Indeed, I have checked as many parts as I can on the board (removing and testing transistors in a multimeter with hFE reading, diode tests, LCR meter and measuring the in line flame proof supply limiting resistors). It all seems good, I am in the teritory now where I keep accidently retesting the same parts lol!
I am prepping to reasemble and have tagged wires onto the main rails in this area (+24 unregulated from LOPT, 12V from IC505 - though this regulator is fine through off board test), 12v from Q520 regulator. I also have a tapping in place on the input to L509 - Pincusion coil. I have measured the parabola on the base of the driver for this coil before though so I think it will be fine.

I have been studying Sams FAQ again, (specifically http://repairfaq.cis.upenn.edu/sam/deflfaq.htm#dsnse) and it has helped a lot in my understanding...

I am wondering if it is a problem with the Cs / S parameter capacitor arrangement on this. It seems a complex variant on this monitor, I cant understand the b+ feed via L514? I have tested all the caps (580, 583, 582, 578) that look to be involved with S correction and they are all good...

Is there any possibility of a slightly failed HOT causing this sort of thing?

The EW circuit is supplied by 24V from the flyback (pin 5). There are safety (flame proof) resistors in series with this voltage (R535, R541, R1514) that could go open. The EW correction waveform is a parabola so if you have a scope check the output of the EW transistor and coil.

[phosphor]

Right, I am mildly closing in on this, but not very fast... I have been doing lots of live probing and have ascertained that all the power rails seem alright, but there is something strange going on around the Pin-Amp IC509 and Pin Drive Q503 (transistor is OK).

So the schematic has a callout on Pin 2 of the Op-Amp IC509 showing a nice pincushion waveform to be expected. This pin is wired to quite a lot of things but I do not get that waveform at that pin...

Expected Pin 2 waveform (No 28):
https://i.imgur.com/ooRXCqR.jpg

Pin 2 Waveform - this is also what seems to be getting fed to the base of the transistor Q503 (or at least almost identical):
https://i.imgur.com/CGhckic.jpg

Pin 3 Waveform - this looks to be the input from the DAC side of things, and the waveform changes with service menu adjustments so I think this is all good on this pin:
https://i.imgur.com/jo49iny.jpg

And the Collector of Q503 gives a fairly steady voltage of around 45-50v but with a small ripple on top, which almost looks like the expected waveform, but does not move with any settings, so I think it is just a coincidence / supply ripple:
https://i.imgur.com/1PdSaHB.jpg

Another interesting note is that Underscan works, but only in the vertical, and horizontal setting from service menu also has no effect... So I do think the problem is in this area rather than the raw deflection side of things.

+24v unregulated from LOPT is about 29V and both 12v regulated rails mentioned prieviously are within a hair width of 12v. B+ is a nice 115v.

Any tips most appreciated

[phosphor]

Right, getting there:



Indeed changing IC509 was I think the main game changer here. Underscan and Overscan now work as well as Horizontal size adjust in service menu (and Pin Adjust).
I did also change out C1518 47uF 16v as it was hitting a dissipation factor of >1 and had sagged to 40uF, though I cant see how that is related.
Also, I changed C565, the cap that was in there was OK but oddly it was 100uF, not 1uF as on the schematic and BOM (and also 1uF on 20M2 service manual).

The image is now ok but not top notch, the OSD text is still green on RGB inputs and Green with White behind on Composite / S-Video inputs. The image wobbles when no sync is input and is a tad hazy, but it could just be me sat 1 foot away from it.

Either way, big step forward. IC509 is a nightmare to get to btw, SOIC-8 surrounded by tall caps and heatsinks.

[kel]

Interesting, I have a PVM20L2 with a very similar layout to that schematic that has an inner pin cushion problem. I am lazy and couldn't be bothered to test parts on the pin circuit , thought it would be easier to just throw parts at it until I found the culprit. I first bought the IC509 (different number on my schematic but still the same IC) that you mentioned a long while ago as it was cheap enough and readily available and then life got in the way and also the other CRTs that I have took priority, needless to say the IC is still sitting there along with two spare damper diodes that I got more recently. Maybe I should make a point of doing that job now being as though you seem to have had some success by replacing that particular part although I suppose there is still no guarantee it will be the same for me as my issue is a little bit different. Oh forgot to mention, this was an ongoing issue before and after a full recap so it's definitely not any of the electrolytics at least.

[buttersoft]

Thank you for keeping us updated more information about CRT maintenance is always valuable.