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Sony PVM-2950 Horizontal Pincushion Problem

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..

Reply to
Ippei Okamura
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On Tue, 15 Jun 2010 12:09:45 -0700, Ippei Okamura ??o??:

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.

Reply to
Meat Plow

=8D:

ptom

arrel

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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.

Reply to
Ippei Okamura

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

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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"
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deflfaq.htm#dsdns).

I'm starting think that PVM-2950 has special circuit that corrects north-south pincushion.. (??)

Reply to
Ippei Okamura

I took some pictures:

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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.

Reply to
Ippei Okamura

On Tue, 15 Jun 2010 20:01:41 -0700, Ippei Okamura ??o??:

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.

Reply to
Meat Plow

On Wed, 16 Jun 2010 11:41:41 -0700, Ippei Okamura ??o??:

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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.

Reply to
Meat Plow

=8D:

re

RPZ"

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...

Reply to
Ippei Okamura

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

Reply to
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...

Reply to
Ippei Okamura

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