Pretty standard MTC9000:
Symtoms: no picture, R105 (330 ohm 30 watt) very warm.
B+ = 2volt
HV= 0
Removed LOPT, ran a 60w lightbulb as a dummy load. B+ voltage returned roughly to spec.
Removed lightbulb replaced LOPT and HOT.
Powered up to see 130+ briefly on B+ and 27+kv HV before x-ray protect kicked in
Searched forums and that handy (French) MTC9000 repair guide. C36 4n7 poly cap tested way out of spec. Replaced cap with one scavenged off a spare chassis (I have about four and the stated value of this cap seems to vary from 3n3 upwards on all of them, even when they use the same LOPT)
Powered up to 132v B+ with ~24kv with no input signal.
Shortly afterwards magic smoke started to escape from near the LOPT just as I saw the B+ drop to 120v and HV also, this prompted swearing and a rapid power down. Found burnt resistor R126 (pin 9 LOPT -> D15 -> R126 -> neckboard 190volts).
Powered up with yoke cable removed to disable HV and put dummy load back on, B+ back to about 130v. checked D15, replaced resistor R126 and both electrolytic caps on neck board.
Powered back up to normal(ish) 132v B+ and 24 KV HV, neck voltage without signal a little on the high side at 210v+, applied signal, dropped to just under 200v (a little high methnks), however chassis remained stable and didn't seem excessively warm.
Midflight montior adjustments revealed another couple of well documented faults in that the 220k brightness preset pot was actually reading 110K (replaced), and horizontal width was too great (replaced dud cap C42) which lives between a power resistor, a heatsink and the LOPT (nice). Width and Brightness preset now okay.
Monitor now works though B+ is 2v above spec and the 190v to the neckboard is somewhat high, possibly worthy of future investigation.
karlcdoe2017-03-31 16:45:26
Symtoms: no picture, R105 (330 ohm 30 watt) very warm.
B+ = 2volt
HV= 0
Removed LOPT, ran a 60w lightbulb as a dummy load. B+ voltage returned roughly to spec.
Removed lightbulb replaced LOPT and HOT.
Powered up to see 130+ briefly on B+ and 27+kv HV before x-ray protect kicked in
Searched forums and that handy (French) MTC9000 repair guide. C36 4n7 poly cap tested way out of spec. Replaced cap with one scavenged off a spare chassis (I have about four and the stated value of this cap seems to vary from 3n3 upwards on all of them, even when they use the same LOPT)
Powered up to 132v B+ with ~24kv with no input signal.
Shortly afterwards magic smoke started to escape from near the LOPT just as I saw the B+ drop to 120v and HV also, this prompted swearing and a rapid power down. Found burnt resistor R126 (pin 9 LOPT -> D15 -> R126 -> neckboard 190volts).
Powered up with yoke cable removed to disable HV and put dummy load back on, B+ back to about 130v. checked D15, replaced resistor R126 and both electrolytic caps on neck board.
Powered back up to normal(ish) 132v B+ and 24 KV HV, neck voltage without signal a little on the high side at 210v+, applied signal, dropped to just under 200v (a little high methnks), however chassis remained stable and didn't seem excessively warm.
Midflight montior adjustments revealed another couple of well documented faults in that the 220k brightness preset pot was actually reading 110K (replaced), and horizontal width was too great (replaced dud cap C42) which lives between a power resistor, a heatsink and the LOPT (nice). Width and Brightness preset now okay.
Monitor now works though B+ is 2v above spec and the 190v to the neckboard is somewhat high, possibly worthy of future investigation.
karlcdoe2017-03-31 16:45:26