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Robotrontechnik-Forum » Technische Diskussionen » K7222.25 repair » Themenansicht

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000
29.04.2022, 13:50 Uhr
Algi

Hey,

Sorry for English, I dont speak German, yet

Looking for help debugging problems in K7222.25 repair.
I have repaired my 1715 PSU, 1715 itself, now its time for the monitor.

Flyback coil was cracked, I have removed it, removed outer coil and istalled it back to test if anything else works ( new coil is in progress ).

After testing without the outer coil, I noticed smoke in resistor R12. I guess the voltage is too high on it. Tested resistor V3, it seems to be ok. Another guess is signal "IS" that goes to resistors V3 base pin is too high.

You can see pictures of mentioned resistor here, at the end of post http://asknotes.com/2022/04/21/robotron-1715-monitor-repair/

With this crt plate connected, monitor consumes 3.8-3.9 amps (resistor burns). If I disconnect it - less that 3 amps.

Just looking for ideas regarding what can cause resistor R12 to burn?

Thanks!

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001
29.04.2022, 13:53 Uhr
Rüdiger
Administrator

Normally the monitor does not smoke if the HV coil is removed.
--
Kernel panic: Out of swap space.

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002
29.04.2022, 13:55 Uhr
Algi

"Normally the monitor does not smoke if the HV coil is removed."

Yes, I know that, it seems there is another problem, just trying to debug it.

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003
29.04.2022, 14:01 Uhr
Rüdiger
Administrator

Is the SU169 still alive? -> Unsolder two pins and use ohmmeter.

btw: inner coil of flyback transformer is not needed if you plan to wind a new coil.
--
Kernel panic: Out of swap space.

Dieser Beitrag wurde am 29.04.2022 um 14:05 Uhr von Rüdiger editiert.

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004
29.04.2022, 14:20 Uhr
Algi

"Is the SU169 still alive? -> Unsolder two pins and use ohmmeter."
I think it was, I remember checking it initially, but will doublecheck this evening.

"btw: inner coil of flyback transformer is not needed if you plan to wind a new coil."
What do you mean? This inner coil is not needed?
http://asknotes.com/wp-content/uploads/2022/04/uha78-could-removed-1.jpg
But according to instructions, it is used?
http://asknotes.com/wp-content/uploads/2022/04/uha78rep.pdf

Also, maybe you know what is normal voltage range for "IS" signal?

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005
29.04.2022, 14:31 Uhr
Rüdiger
Administrator

Zitat:

Algi schrieb
"btw: inner coil of flyback transformer is not needed if you plan to wind a new coil."
What do you mean? This inner coil is not needed?

That transformer was developed for a TV set, not for this monitor.
To reuse the transformer for computer monitor, Robotron soldered two coils in serial.
If you are winding a new coil you can better do some revolutions more at new coil.

btw: possibly the insulation is firing inside to the core. Check the hole for discoloration.
--
Kernel panic: Out of swap space.

Dieser Beitrag wurde am 29.04.2022 um 15:30 Uhr von Rüdiger editiert.

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