Nanao MS8-26SU. Red screen and retrace lines?

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nem
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Nanao MS8-26SU. Red screen and retrace lines?

Post by nem »

I have a busted MS8-26SU that I have been trying to fix. Originally it had a collapsed screen. I swapped out the blown R433 resistor and recapped it. Turning it now on I have a normal sized screen.

All is still not well, however, as the screen is mostly red with retrace lines. I turned down the color cutoffs and gains, brightness and screen voltage. I still have a bright red screen with retrace lines :problem:

I checked and adjusted B+ voltage. 92V on the nose.

Calling Grant!
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grantspain
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Re: Nanao MS8-26SU. Red screen and retrace lines?

Post by grantspain »

desolder red gun pin on the crt socket
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nem
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Re: Nanao MS8-26SU. Red screen and retrace lines?

Post by nem »

I desoldered the red pin and I now I get a black screen.

I resoldered it back and measured voltage on all the RGB pins. G and B are showing 116V, R is 16.5V.
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grantspain
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Re: Nanao MS8-26SU. Red screen and retrace lines?

Post by grantspain »

problem is on the red drive circuit then
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nem
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Re: Nanao MS8-26SU. Red screen and retrace lines?

Post by nem »

Any ideas on where I should focus my efforts on?

EDIT: I swapped the neck board from a working chassis and the problem went away. So it's somewhere on the neck board. I guess I'll just swap parts between the color circuits unless there's a better way? I already tried changing the big transistor, that one was OK.
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nem
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Re: Nanao MS8-26SU. Red screen and retrace lines?

Post by nem »

Found the problem in the red circuit :awe: A diode and resistor were blown.
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RMRM
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Re: Nanao MS8-26SU. Red screen and retrace lines?

Post by RMRM »

:slowclap:

Great! Always good to share.
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