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From: Meat Plow on 16 Jun 2010 15:33
On Tue, 15 Jun 2010 20:01:41 -0700, Ippei Okamura ǝʇoɹʍ:

> Just to clarify, the following is the drawing of the symptom:
> _________________________
> | \ / | | \
> / | | +__________________+ | @
> | | |
> | | | |
> | | +------------------------------+
> | @ | / \ | | /
> \ | --------------------------------------------
>
> @: in reality, these lines follow smooth curve towards center of screen.
>
>
> I'm starting to get confused with terms "horizontal pincushion" and
> "vertical pincushion"...
> But I believe that the symptom shown above is called "north-south
> pincushion".
>
> The article "TV and Monitor Deflection Systems" by Samuel M. Goldwasser
> (http://www.repairfaq.org/sam/deflfaq.htm) is very helpful.
> In this article, I found that north-south pincushion is difficult to
> handle and it is better to design deflection coil so that "the picture
> tube needs no active N/S correction" (http://www.repairfaq.org/sam/
> deflfaq.htm#dsdns).
>
> I'm starting think that PVM-2950 has special circuit that corrects
> north-south pincushion.. (??)

Somewhere I recall a DZ board for either convergence or as a pincushion
amp or even both. Sorry wasn't much of a Sony tech back in the day but I
have some Trinitron experience.
From: Meat Plow on 16 Jun 2010 15:47
On Wed, 16 Jun 2010 11:41:41 -0700, Ippei Okamura ǝʇoɹʍ:

> I took some pictures:
> http://picasaweb.google.com/117475674374880339742/PVM2950Q?
feat=directlink
>
> I tried adjusting in service mode. I was able to fill up the entire
> screen with image but bowing doesn't go away. I noticed that "H TRPZ"
> has very little effect on the screen.
>
> Any comments or suggestion will be greatly appreciated.

I guess that is the horiz trapezoid adjustment. Keep at it you'll figure
it out. Might help to have some technical literature on the set.
From: Ippei Okamura on 16 Jun 2010 19:29
On Jun 16, 2:47 pm, Meat Plow <mhyw...(a)yahoo.com> wrote:
> On Wed, 16 Jun 2010 11:41:41 -0700, Ippei Okamura ǝʇoɹʍ:
>
>
>
> > I took some pictures:
> >http://picasaweb.google.com/117475674374880339742/PVM2950Q?
> feat=directlink
>
> > I tried adjusting in service mode.  I was able to fill up the entire
> > screen with image but bowing doesn't go away.  I noticed that "H TRPZ"
> > has very little effect on the screen.
>
> > Any comments or suggestion will be greatly appreciated.
>
> I guess that is the horiz trapezoid adjustment. Keep at it you'll figure
> it out. Might help to have some technical literature on the set.

Thanks again!

I think all controls in service mode are working, except the
horizontal trapezoid whose effect is small. Looking at the block
diagrams in service manual, all of A (main with flyback), DX
(GEOMETRIC DISTORTION CORRECTION), and VC (V. PIN DRU, Vcc DRU, TILT
CORR) boards seem to have something related to pincushion. DX and VC
boards are sub board that are plugged on to A board.

A board: IC502 ("PIN CORR", UPC393C, 8pin bipolar analog IC), Q506
("PIN OUT", 2SK1916-53-F50), Q508 and Q509 ("PIN DRV", 2SD774-34 and
2SB733-34), T1801 ("VPOT", FERRITE TRANSFORMER), and L1802 ("", COIL
(WITH CORE)).

DX board: IC1506 ("D/A CONV", CXA1315M, pin-6 is labeled TRPZ and
traces to VC board), and IC1505 ("SAW PARA OUT", BA10358F, op amp)

VC board: IC1803 ("V-PIN-DRU", SN74LS221N, Dual Monostable
Multivibrators With Schmitt-Trigger Inputs), IC1802 ("Vcc DRU",
2SA1175-HFE), Q1804/1805/1809/1810 ("V PIN DRV 1/2/3/4", 2SA1175-HFE,
2SC2785-HFE), Q1811 ("V.PIN OUT 2", 2SC3298B-0), Q1806 ("V.PIN SW1",
2SB858-C)

From my understanding on the article I mentioned previously, N/S
pincushion is normally corrected "by using a 'transductor'.", "a
component with 2 coils and a saturable core". Looking at the diagram
on A board, there are L1802 and T1801 that are connected to VC board
with lines called V-PIN-H and V-PIN-V, respectively. At the end(?) of
VC board, lines called "SKEW+" and "SKEW-" go to Deflection York. I'm
guessing they might function as a "transductor" mentioned in the
article but I'm not sure...
From: Chuck on 17 Jun 2010 09:40
On Tue, 15 Jun 2010 12:09:45 -0700 (PDT), Ippei Okamura
<tanupei(a)gmail.com> wrote:

>Hello,
>
>I have Sony PVM-2950 with pincushion problem.
>The image bows toward the center of the screen from both top and
>bottom. I believe this symptom is called "horizontal" or "north-
>south" pincushion problem.
>I tired to adjust it in service mode, but I was unable to control the
>amount of bowing at top and bottom of the screen. I can control
>barrel shaped pincushion (east-west) but it does nothing on top and
>bottom of the screen.
>
>Is there anything that I can adjust horizontal pincushion without
>opening the set?
>Could somebody please give me a clue on what is causing this problem
>and where and what to look for?
>I have a service manual but because I am not an expert, only thing I
>can think of is some failure in VC, DX, or part of A board.
>
>This is first time I'm posting, so please let me know if I'm doing
>something wrong.
>I would appreciate any response..


Do you have an ESR meter? We usually find many bad electrolytics in
the deflection circuits of these units. Electrolytic failure causes
the majority of all failures on this model including pincushioning.
Chuck
From: Ippei Okamura on 17 Jun 2010 11:21
On Jun 17, 8:40 am, Chuck <c...(a)deja.net> wrote:
> Do you have an ESR meter?  We usually find many bad electrolytics in
> the deflection circuits of these units. Electrolytic failure causes
> the majority of all failures on this model including pincushioning.
> Chuck

Thank you for reply!

No, I don't have ESR meter. Only tool I have is 29-Range Digital
Multimeter from RadioShack.
For N/S pincushion problem, could you please specify which
electrolytics I should be looking? Or maybe just an idea on what area
or which board? I'm guessing C18xx's in VC board and C5xx's in A
board but since I'm not a professional repair person, I cannot be sure
about it...
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