Sony PVM-2950 Horizontal Pincushion Problem

I

Ippei Okamura

Guest
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..
 
On Tue, 15 Jun 2010 12:09:45 -0700, Ippei Okamura ǝʇoɹʍ:

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..
Click to expand...
I've read somewhere those things have a hidden Optimode test pattern in
the service mode usefull for pincushion and convergence. But I have no
idea how to access it.
 
On Jun 15, 4:13 pm, Meat Plow <mhyw...@yahoo.com> wrote:
On Tue, 15 Jun 2010 12:09:45 -0700, Ippei Okamura ǝʇoɹʍ:



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..

I've read somewhere those things have a hidden Optimode test pattern in
the service mode usefull for pincushion and convergence. But I have no
idea how to access it.
Click to expand...
Thank you for reply!

Yes, if it can generate such pattern by itself, it would be really
helpful.
I heard that Sony BVM series can generate cross-hatch by itself but
that series is for mastering at broadcast stations and might cost
triple of PVM series.
 
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.. (??)
 
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.
 
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.. (??)
Click to expand...
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.
 
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.
Click to expand...
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.
 
On Jun 16, 2:47 pm, Meat Plow <mhyw...@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.
Click to expand...
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...
 
On Tue, 15 Jun 2010 12:09:45 -0700 (PDT), Ippei Okamura
<tanupei@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..
Click to expand...

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
 
On Jun 17, 8:40 am, Chuck <c...@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
Click to expand...
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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