Pioneer SP-D4561 pincushion problem

[JURB6006]

Hi;

This one is too wide. The width control only works way at the bottom and
doesn't have enough range. It actually starts pulling the top and bottom of the
sides in first, so it actually works, just not correctly. (I of course had
already checked for a shorted pin transistor etc.)

When it's turned down the width slowly changes with variations in beam current.
It's like a job I had awhile back where I modified the circuit because it was a
rush job. I would rather not do that this time because the problem is not on
the (standup) geometry board, or whatever they call it. It has been tested by
substitution.

One of the inputs to that board must be missing, and I'll bet there's a bad
100K resistor hiding somewhere. Following the circuit best I can without a
print I found a 47K that seems to be for the purpose of providing feedback from
the pin output, but it's good. Perhaps one of the other inputs ? The AC
component of the drive is OK, it's strictly the DC part driving the pin output
into saturation.

If the HV feedback was missing, my guess is that the raster would be too narrow
(guess mind you), the beam current is affecting it so that is probably OK
(probably). There's not much left, or perhaps I got two standup boards with the
same fault ? Not that likely, the replacement came out of a set that had been
hit pretty hard by lightning, or can bad ESD or static cause a specific failure
on those ?

I am without print on this one, any help is greatly appreciated.

Thanks in advance.

JURB

 

[Tom W]

On the side of the board that has the size adjustment pots, to the left (on
the parts side of the board) is a blob of white glue over a couple of parts.
remove the glue and resolder the parts. this solved the problem for me on
two units with the same symptom.

tom w