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Toshiba TV-37C60 pincushion (hard one).

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

Reply to
Jason D.
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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

Reply to
Doug

On Fri, 01 Apr 2005 00:19:09 GMT, snipped-for-privacy@sympatico.ca (Jason D.) put finger to keyboard and composed:

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

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- Franc Zabkar

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Please remove one 's' from my address when replying by email.
Reply to
Franc Zabkar

"Jason D." bravely wrote to "All" (01 Apr 05 00:19:09) --- on the heady topic of "Toshiba TV-37C60 pincushion (hard one)."

JD> From: snipped-for-privacy@sympatico.ca (Jason D.) JD> Xref: aeinews sci.electronics.repair:44635

JD> This big tv has pincushion problem (bowed in), did basic checks on JD> capacitors and diodes in series within horizontal circuit, ESR check JD> on pincushion board (stand up) board next to this horizontal heatsink JD> and scoped the board and adusted two pots for width and pincushion, it JD> works as it should be. [,,,] JD> On pic with width pot, can change width no problem but pincushion JD> seems to effect very limited, except it acted like bowed trapazoid JD> which this chassis does not support. :)

JD> I"m stumped.

JD> Cheers,

Could be the diodes are leaky.

A*s*i*m*o*v

... If all else fails, hurl it across the room a few times!

Reply to
Asimov

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

Reply to
Jason D.

UPDATE and NO FIX YET:

Swapped out one 2SC1815 transistor (barely weak) that is driving the main amp pincushion transistor. Helped bit on that problem but had to turn that pincushion pot all the way to one direction.

While working on other area of that TV to cool chassis off and turned it back on, hey, one sided pincushion problem (right side bowed), gradually straightens out within a minute. Left side is straight.

Not fixed yet! That one (slowly straightening out from cold start) and pot all the way to one side should make pincushion into barrel (bowed out) but yet it didn't.

Any other solutions?

Cheers, Wizard

Reply to
Jason D.

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