Electronics > Repair

Sony PVM-1271Q

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mattswensson:

--- Quote from: jeremybh1 on June 10, 2023, 02:59:41 am ---
I've opened the latest supplied photo in full and it's more than a pin issue - I say this as my understanding was pincushion correct is last mile sort of thing; you don't have full horizontal deflection, far from it.  Sure the is pin cushion issues but why is the raster 3/4 wide

--- End quote ---

If you are referring to my photo of Rockman 5 video game, I actually decreased the horizontal width just so it is clear the extent of the curve.  When I grow it back to the width of the screen, the problem is still there, but it is kind of 'clipped' off screen so that is the reason for my decrease in width.  I really need to get the grid on the screen which I'll try to do this weekend.

Thanks again for everyone's help and guidance.  Hopefully we can both get our issues resolved.

mattswensson:
Or maybe you are saying that this is so severe it isn’t a pincushion thing because that is more of a slight tweak?

elecdonia:

--- Quote from: mattswensson on June 10, 2023, 04:28:39 am ---If you are referring to my photo of Rockman 5 video game, I actually decreased the horizontal width just so it is clear the extent of the curve.  When I grow it back to the width of the screen, the problem is still there, but it is kind of 'clipped' off screen so that is the reason for my decrease in width.
--- End quote ---
The good news is that your “Normal H width” trimmer is causing the screen image to get narrower and wider. This confirms that most of the pincushion circuit is functional.

Check down a few posts in this thread for my description of the signal path.

The pincushion circuit requires a “ramp” (sawtooth) input signal which originates from the horizontal/vertical oscillator IC. This IC is still functional because both horizontal and vertical deflection are present.
Therefore the most likely fault is with this vertical frequency ramp signal failing to get all the way to the pincushion IC.
The ramp signal itself is at 60Hz (50Hz for PAL/SECAM modes) and its amplitude probably about 1V.

The best way to follow its progress is with an oscilloscope.

mattswensson:
Awesome...so I want to hook up my oscilloscope without frying it.  This rig seems to have earth ground and the ground plane all going to the same place (?)...I assume I need an isolation transformer before I hook my scope up correct? or is there some ground point on this machine I can safely leverage.

elecdonia:

--- Quote from: mattswensson on June 09, 2023, 10:09:09 pm ---UPin and NPin amps and phases all have SOME effect, the YBOW adjustment has little to no impact.
--- End quote ---
The N-pin-amp trimmer should have a considerable effect on the )-|-( vs. (-|-) curvature at the extreme left and right edges of the screen. The “N” trimmers may interact with each other. Getting perfectly straight left and right edges may require several rounds of tweaking.

It is logical that all “N” trimmers  should get adjusted first. Then switch to “underscan” mode and adjust the “U” trimmers. I would expect the “U” trimmers to have no effect when the normal/underscan switch is set to “normal.” One of my thoughts is the “normal/underscan” switch might need its contacts cleaned. If the “U” trimmers are changing the shape of the screen image while switch is at “normal” then this portion of the circuit needs more attention.

As for the “BOW” trimmers I think they provide a very small adjustment to make a vertical line located in the middle of the screen perfectly vertical. These “BOW” controls are not part of the pincushion circuit. Rather they do something with the timing of the sync signals. My best guess is that BOW should have this effect: At one end of rotation: (-(-(. In the middle: |-|-|.  And all the way at the other end of rotation: )-)-). This is likely to be a very small effect. Perhaps only a few mm deviation from perfectly vertical.

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