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From: Jason D. on 31 Mar 2005 19:19
This big tv has pincushion problem (bowed in), did basic checks on
capacitors and diodes in series within horizontal circuit, ESR check
on pincushion board (stand up) board next to this horizontal heatsink
and scoped the board and adusted two pots for width and pincushion, it
works as it should be.

Sigh!! Pulled the schematic out and checked voltages on IC482
(TA75558S), Two pins looks bit off. Pin 6 is solid 9V and it is fed
via resistor divider directly from the flyback HV and the ground. The
other pin 2 on that IC is slightly higher. Q480 collector should be
150V, I'm getting about 98V, base is about .7V, should be .5V. The B+
is 125V as it should be.

Only one cap I'm suspicious about is the pincushion board (DPC,
PB3235) located CD11, the schematic calls for 10uF 100V in part
listing and the schematic agrees but the replacement cap was in it is
100uF 250V. I pulled out a replacement capacitor, and I'm not
comfortable with using that new cap because the silkscreened outline
of capacitor is larger than the new capacitor I have here.

I do get paraola and ramp waveforms feeding DPC (pincushion board)

When I adjust the pincushion pot on DPC, I can get paraola deeper or
shallower, width pot can make whole waveform riding on speific
voltages move up and down.

On pic with width pot, can change width no problem but pincushion
seems to effect very limited, except it acted like bowed trapazoid
which this chassis does not support. :)

I"m stumped.

Cheers,

Wizard
From: Doug on 31 Mar 2005 21:28
I lost dial up connection so this may be a double post.
Great information on what you did.
The only thing I have is on USA sets cx35c60 ,cn35c90 1994 sets is a
modification from Toshiba part number 23305500 which has the
instructions and 2 each resistors and caps to add to pin 10 of IC501.
This is for correction of left side pincushion. Might check wih Toshiba
were you're at or parts distributor and see if they have a kit for
you're model.
Doug

From: Franc Zabkar on 1 Apr 2005 01:54
On Fri, 01 Apr 2005 00:19:09 GMT, jpero(a)sympatico.ca (Jason D.) put
finger to keyboard and composed:

>This big tv has pincushion problem (bowed in), did basic checks on
>capacitors and diodes in series within horizontal circuit, ESR check
>on pincushion board (stand up) board next to this horizontal heatsink
>and scoped the board and adusted two pots for width and pincushion, it
>works as it should be.
>
>Sigh!! Pulled the schematic out and checked voltages on IC482
>(TA75558S), Two pins looks bit off. Pin 6 is solid 9V and it is fed
>via resistor divider directly from the flyback HV and the ground. The
>other pin 2 on that IC is slightly higher. Q480 collector should be
>150V, I'm getting about 98V, base is about .7V, should be .5V. The B+
>is 125V as it should be.

This IC is a dual opamp. If it is operating in its linear region, then
the voltages at pins 3 and 4 should be identical, as should those at 6
and 7. If you are suspicious of this IC, then install it backwards, ie
interchange pins 1 and 9. The datasheet states that this is OK as the
device is symmetric.

See http://www.spelektroniikka.fi/kuvat/ta75558s.pdf


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.
From: Jason D. on 1 Apr 2005 23:21
On Fri, 01 Apr 2005 16:54:17 +1000, Franc Zabkar
<fzabkar(a)optussnet.com.au> wrote:

>On Fri, 01 Apr 2005 00:19:09 GMT, jpero(a)sympatico.ca (Jason D.) put
>finger to keyboard and composed:
>
>>This big tv has pincushion problem (bowed in), did basic checks on
>>capacitors and diodes in series within horizontal circuit, ESR check
>>on pincushion board (stand up) board next to this horizontal heatsink
>>and scoped the board and adusted two pots for width and pincushion, it
>>works as it should be.
>>
>>Sigh!! Pulled the schematic out and checked voltages on IC482
>>(TA75558S), Two pins looks bit off. Pin 6 is solid 9V and it is fed
>>via resistor divider directly from the flyback HV and the ground. The
>>other pin 2 on that IC is slightly higher. Q480 collector should be
>>150V, I'm getting about 98V, base is about .7V, should be .5V. The B+
>>is 125V as it should be.
>
>This IC is a dual opamp. If it is operating in its linear region, then
>the voltages at pins 3 and 4 should be identical, as should those at 6
>and 7. If you are suspicious of this IC, then install it backwards, ie
>interchange pins 1 and 9. The datasheet states that this is OK as the
>device is symmetric.
>
>See http://www.spelektroniikka.fi/kuvat/ta75558s.pdf
>
>
>- Franc Zabkar

More findings, I did flip that TA75558S, no change. But I noticed one
thing, on collector of the Q480, if I put up white picture, the
voltage rises to barely 150V but if I put up grid, volts falls back to
around 89V. The TA75558S pin 6 still solid 9V. If I adjust the IC,
it has 9.1V pot to set up for 9.1V, if I vary it, the collector of the
Q480 varies massively.

YET the stupid pincushion problem still is unchanged. And I'm no
closer to this solution.

Cheers, Wizard
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