Hi all , I have an old monitor with a problem : it power up build the HV and shut down after 1 sec.
Few times it show the image but it decreases and becomes too bright and shutdown after.
I change the electrolitic caps from PSU and C707 was changed with a superior value to increase delay of HV.
Now i can power the unit in this form : push the power button the image show up few seconds like 2 sec or less then shut off ,and push power button few times and the image show again I hear the yoke ringing but increase in dimensions and decrease (have a breathing effect) and after is stable. The breathing effect is present also when change the resolution but less aprox 2%.
I think is a dried capacitor but I can't find it.
The PSU tension is correct with no deviation. The 185V rail seems to be OK.
I see that the unit collapse the HV Q507,Q728 don't oscilate and the yoke not ringing.
Have any ideas to fix this problem ?
Thank's in advance.
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Hi this maybe due to the internal capacitor in the FBT going low in value. This causes the eht to rise quickly and overshoot and cause the xray protect to cut in.
Remove C743 6.8uF 50V this still leaves C766 the same value on the same line.
This will let the EHT rise more slowly and may cure your problem.
If it does it means that the FBT capacitor has reduced in value.
Rich
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Our schematics seems not to be the same because mine C743 have 10uF/50V and C766 doesn't exist.
I can send you my schematic it's 100% according to the unit if you want and give me your mail address.
Thank you for waste your time to read here.
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