Nanao/Sega MC-1400 Verticle Deflection Problems.

[Hooligan93]

Hi Everyone,

Didn't want to high-jack the other MC-2000 thread (not sure what the rules are)  . I just got my MC-1400 out of vertical collapse with a cap kit from Ian Kellogg (thank you for the quick shipping), and also Vertical Deflection transistors.

While testing the B+ i accidentally shorted the test lead and reeked havoc on the power circuit. I blew the 0.750Amp fuse plus the voltage regulator. spent the last couple weeks testing resistors, diodes, transistors, and rectifier bridge, but the monitor keeps going into high voltage shutdown.

 My B+ was at 141vdc (should be at 105vdc according to the schematics). Turning the B+ pot as low as it will go i can get it down to 119vdc which gives me picture but I cant get rid of the scan lines and my vertical deflection is still a bit screwed up.

Any ideas where to look next in the power circuit? Any ideas for the vertical deflection problems? Really need a monitor guru.

[Hooligan93]

Ended up replacing the voltage regulator, and the two defection transistors Q401 Q402. This moved the vertical defection problem to the top 1 inch of the screen. I kept playing with the B+ pot eventually I think it cleaned itself up and my B+ came into spec with room for adjustment on the pot. I then remembered I found a ceramic Cap in the bottom of the cabinet and a partial leg on Q402 so I experimented a bit and sure enough putting the cap on the emitter and collector solved the vertical deflection problem. The monitor is now 100% working just have some color adjustments to do.

BTW I grabbed a cheap Chinese esr meter (it also tests transistors too) and most of the original caps were way out of spec on esr and uF.