[Solved] PVM monitor repair

[fabiodl]

I have a sony PVM-204M
Its service manual is here

All of a sudden, I got the RED, GREEN & BLUE lines displaying on the top of the screen as shown


I fully recapped it (155caps!) but the problem remains. Indeed, the ESR of every single cap was ok.

I am worried connecting a faulty console to it may have damaged it.
Video signals are still shown correctly, so let's say a faulty power brick let 110V through the console and through the video inputs. Wouldn't that have damaged the whole input section? However it's only the vertical position which shifted all of a sudden.

What would be your next action?

[perieanuo]

the menu shows up ok? if it shows, then yes you have popcorned your input stage

[perieanuo]

on page 42 i see some input list, which one you used?

[fabiodl]

All inputs still work (the image comes out fine), but it is vertically shifted down.
The menu is shifted in the same way.

[Ian.M]

Later model Sony CRT monitors and TVs have auto white balance, performed by measuring the individual R, G and B electron gun beam currents (to control for decreasing emission) on three scanlines during the vertical blanking interval. If the vertical timebase circuit is faulty, its not uncommon to see them on screen.

It is *EXTREMELY* unlikely to be caused by damage from a possibly faulty console, and the only possible way that could happen and still leave it capable of showing a synced stable picture would be if the console used a frame rate right on the margin of what the monitor could accept, which could have over-stressed an already weak and failing vertical output stage.  If it had input stage (or input selector) damage, it would have problems displaying one or more colors and/or if the sync inputs were damaged, the picture would either be unstable or blanked.

[Runco990]

You need to go into the service menu and re-adjust the Vertical and Horizontal settings.  Typical after a re-cap.  I used to repair these by the pallet load back in the studio days before we switched to HD.

Possibly also the vertical blanking on top, as this can cause the white balance lines to come down too far.

[fabiodl]

I did the recap because if this problem. I did enter the service menu. By adjusting v-blanking I can move the lines up, but the even the maximum value is not sufficient to bring the image to the center

[Ian.M]

Are there any geometry problems?  Try displaying a grid of squares + diagonal lines and look for any vertical linearity defects.  If found, go over the vertical output stage looking for low ohm resistors that have changed value, diodes that have gone open or short, and dry joints, especially on inductors.

Also, did you use good, name brand 105 dec C caps in the vertical section?

[fabiodl]

There are no other geometry problems. All the caps are Nichicon, 105degrees, long life.
I tried wiggling the board / pushing it with a plastic stick while in operation, but I saw no difference.
I checked the value of the resistors near the heatsinks (I checked only the through hole ones,though),but they were spot on.
I will have a check at diodes, thank you.

[Runco990]

Did you change any values in the Vertical circuit?  In particular the 4.7 uF and maybe a 1uF or 2.2uF?  Don't!  I forgot the exact ones after so many years, but the set doesn't like it.  One is usually orange in color, if I recall.  Next to one of the vertical transistor heatsinks.

[fabiodl]

C-572 and C-584,isn't it.
It's indeed the orange one, close to the heatsink. The board mounted a 1uF cap, but the service manual listed 2.2uF (according to the linked video, the change was published in a service bulletin from sony).
I tried both values, but I got no change at all. I replaced the 4.7uF one with a 4.7uF.

[perieanuo]

the op says he had problems before recap, so maybe changed values isn't the thing
V-blanking adjustment works? pages 28-29
v-size adjustment works?

[fabiodl]

Yes, the problem start before the recap.
The service menu adjustments work in the sense that I see the image change on the screen, but even the maximum values are not enough to center the picture.

[Kerlin]

Why would you replace all the caps?
Some comments that follow are also really dubious.
Take it to some one who has been trained and experienced to do such to do such work, it wont cost much.
If the cost is too much then throw it out.

When I was young and family or a friend had faulty electronics equipment my farther would show his knowledge of electronics by saying " Oh that will be a capacitor"  sometimes just to balance it out he would say "Oh that will be a short".
People thought he was smart and he felt smart.
After I was trained, qualified and experienced I realized he knew nothing about electronics, he was a bus driver!!

He couldn't describe the symptoms and even if some one gave him the reason for the problem he wouldn't understand it.

[Ian.M]

CRT TV and monitor repair is a dying trade, and has been for over a decade, so its getting harder and harder to find a repair shop that still handles them, and the few specialists that do wont be cheap. 

As CRT TVs and monitors are no longer in production, yet are still in demand by the gaming and retro-arcade communities, and Sony CRT monitors used to be known for their quality, even if its BER (which is unlikely given the symptoms described unless a unobtanium Sony chip is fried), it should still have some value as a parts donor, so please don't scrap it without trying to find someone who wants it.

[pcwrangler]

Take it to some one who has been trained and experienced to do such to do such work, it wont cost much.
If the cost is too much then throw it out.

I'm not sure your post follows the spirit of this forum. Many here have saved electronics destined for a landfill, get this, without training or official education.

I encourage the OP to do anything they can to save their equipment, safely. As another contributor just posted, please don't throw out a PVM monitor without trying to give away or at least sell it. Good luck!

[sean0118]

Replacing the caps wasn't a waste of time, once you get it fixed it will be less likely to fail again in the future, as electrolytics do have a finite life. 

[perieanuo]

Yes, the problem start before the recap.
The service menu adjustments work in the sense that I see the image change on the screen, but even the maximum values are not enough to center the picture.

that narrows to vertical deflection the fault, in page 41 you have the big picture
you say you cannot center the V, but size it's ok?
you gotta be more explicite to narrow down the defective area, tbo a scope would be gold for this job, verifying the V sync pulses (IC507 pins 22/20/19 they say) would eliminate half of the problem, my experience with tv's is that is almost always the power stages falls first, some capacitor or resistor in that area

[fabiodl]

I am now checking the parts' value (at the moment, only for the ones for which that can be done in circuit),
and the continuity of the traces, starting from V+ V-.
I have a question though. What is a reasonable value for the thermistor TH-500? I read 56 ohms at ambient temperature.

that narrows to vertical deflection the fault, in page 41 you have the big picture
you say you cannot center the V, but size it's ok?
you gotta be more explicite to narrow down the defective area, tbo a scope would be gold for this job, verifying the V sync pulses (IC507 pins 22/20/19 they say) would eliminate half of the problem, my experience with tv's is that is almost always the power stages falls first, some capacitor or resistor in that area

Yes, the size looks ok.
I have a scope,I'll check and report. As for pin 19 and 20, I believe the correct pulses are the one shown for test points 55 and 54 (page 71), respectively.
What kind of signal would you you expect on pin 22?

[fabiodl]

I noticed one strange thing. The menu seems to be shifted, but the signal not so much.
See the attached picture.
The top pictures show the monoscope, and the menu, with underscan.
The bottom pictures show the same things, without underscan.

As you can see, the top of the image is  replaced by the retracing lines.

[perieanuo]

in that manual, i see vertical/horz deflection brain at page 59-60 IC507, waveforms for H/V deflection are on page 61 (54, 55 and so on)
we're watching different things

[perieanuo]

the bizarre part is vsync and hsync came from different parts (see ic503/502), not easy to track this
but my intuition says the problem is before vsync (video v) attack ic507 on pin 22, in ic502-503 area or before this

[fabiodl]

Yes, I think you are correct, but one thing puzzles me. Why does the menu get shifted, but the picture does not? if vsync was delayed, I would expect the image to shift down as well

[Runco990]

This doesn't make sense to me.... seems like someone may have played around in the service menu and messed everything up.  The menu position is also adjustable, btw.

You are not doing a bonehead move like adjusting it in 16:9 like I did once?

But I have seen these with every setting totally screwed up and it took a total setup to get everything balanced out again.  I may be wrong, but I have never found these monitors to have any problems other than the 2 caps.  They were absolute tanks.

Now the 20M"4"U had crt problems, but the 20M2U is basically a PVM 1954Q at heart.  They just ran forever.

[james_s]

Replacing the caps wasn't a waste of time, once you get it fixed it will be less likely to fail again in the future, as electrolytics do have a finite life. 

That depends on whether they were replaced with good quality caps and the work was done properly. Multiple times I've had people bring me stuff to fix that they had either replaced good quality caps with the cheapest random no-name junk they could find, or bungled the job and done damage that wasn't there before. IMO it's best to fix the problem *before* shotgun replacing capacitors.