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Monitor IBM 6547-2BN fault

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sawwa7

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ibm6547

hi all colleagues
i have this IBM 6547-2BN built on samsung chassis CKB5237L which is dead apart from the power green led blinking once a second (nearly) and the relay clicking on power up . All the supply reails are comming correct and i can measure 50V on Collectors of both Q503 and Q406 , couldn't find any short horizontal area , all the supply rails of power supply are comming correct , 50V,80V,13V,7V,-12V .. all are ok except the missing 12V which comming from pin 2 of IC603 which measures about 1.1V and was disabled by Q604 (suspended by MCU) , if i disconnect Q604 base the 12V commes up again wich reveals non-faulty IC 603 , checking both Hsync and Vsync inputs @ pins 24 and 15 of IC 202(MCU) , proved they are present , also they come out of pins 21 and 20 of MCU , i have ocsillator activities around the crystal pins which reavel a working oscillator and crystal .
the supply voltage to MCU is 5.5 to 5.6 V @ pin 10 and there's 5.5V also present @ pin 25 of MCU , the supply voltage is regulated by IC600 which drops down the 13V supply rail to 5V for micon .. i couldn't find anything wrong or missing ??!!
one more thing i've noticed is pin 12 of MCU , H-Protect is high (5 to 6V) ,this indicates an OCP mode , when i disabled this , the HOT Q503 got very hot and no raster appeared .. does this means a faulty FBT?
any help or hint would be greatly appreciated
regards

Added after 5 hours 18 minutes:

hi again
here's the service manual for this monitor in case someone needs it or wanna have a look to help
Regards
 

ramonglez59

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It may be FBT, you can check this making a frecuency measurement in driver Trs, on base you must be the oscilator frecuency and the colector must be double of frecuency on it or in horizontal out
 

sawwa7

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hello ramonglez59
that post was so old and it turned out to be the FBT .
thanks for trying help
Good luck
Regards
 

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