Sony 61XBR38 with Pincushion problem

[BWL]

This is the one with the H.V. board mounted on a metal box on top of the power
supply; uses STK4278L's for convergence. Convergence working fine, but pic has
obvious horizontal and vertical pincushion distortion. I'm hoping somebody has
seen this problem on this type chassis before, since I don't have the 15 piece
Sony service cable set, and the service manual is a reprint, with the large
schematics cut into eight pieces and sequentially bound into the manual(what a
pain). It's NOT the convergence circuit, as I have +/- 17 volts to the IC's and
they are running normally warm (hot). I could almost get it corrected using the
adjustment pots, but that's not the right way to fix this; any help?

 

[JURB6006]

Doesn't matter, on these all three vert ckt are on the convergence board as
well as the WF generator for the minimal E-W correction provided by the main
deflection.

Smack the convergence board around a bit and you might just find the problem
right there. If it is N-S pincushion, it is definately there, that is handled
100% by the convergence, or nearto. The parabola that feeds the Hout modulator
is on the convergence board, and master side pincushion is about all the
chassis corrects.

In a nutshell, your problem is 99% chance on the convergence board even if it
didn't blow it's nuts off yet.

JURB

 

[Alan Harriman]

This is the one with the H.V. board mounted on a metal box on top of the power
supply; uses STK4278L's for convergence. Convergence working fine, but pic has
obvious horizontal and vertical pincushion distortion. I'm hoping somebody has
seen this problem on this type chassis before, since I don't have the 15 piece
Sony service cable set, and the service manual is a reprint, with the large
schematics cut into eight pieces and sequentially bound into the manual(what a
pain). It's NOT the convergence circuit, as I have +/- 17 volts to the IC's and
they are running normally warm (hot). I could almost get it corrected using the
adjustment pots, but that's not the right way to fix this; any help?

Check for shorted Q508 (2sa1301-0) on the A board. It's the large transistor
located near the upper left corner of the board. Sony # 872920416. Also check
solder connections on the two large film caps, C512 & C510, especially check the
eyelets. Poor connections will cause Q508 to overheat.

Alan Harriman