Naomi Monitor Slowely Expands Picture

OldFoo · Post by **OldFoo** » Thu Aug 27, 2009 11:26 pm

I have had this a couple of times now if diff cabs and would like to track down the solution.

The monitor works fine, picture is clear etc.. BUT... power on and the geometry is spot on, 10 mins later and the horizontal and vertical have stretched to about an inch of the screen, can adjust back using pots, 20 mins later and picture has expanded even more on both axis. Turn of the power and leave to cool down, if you adjusted the pots to make the picture fit after being on 20 mins then when you power back up from cold the picture has a black border until it slowely stretches back out again..

Whats causing this, caps ?... or a specific cap or component.

Any help would be very welcome in tracking down the offending component(s).

Thx in advance

OldFoo · Post by **OldFoo** » Thu Aug 27, 2009 11:40 pm

not affected by tapping the chassis?

if not then a cap,width transistor or east/west diodes or maybe something to do with the b+ circuit

OldFoo · Post by **OldFoo** » Fri Aug 28, 2009 5:27 am

Same problem, explain here. But no solution

http://www.sega-naomi.com/forum/viewtopic.php?t=3221

OldFoo · Post by **OldFoo** » Fri Aug 28, 2009 9:03 am

tapping does nothing, chassis is clean and free from dust. Picture expands equally both in height and width so must be something that affects both horz and vert circuits together.

OldFoo · Post by **OldFoo** » Fri Aug 28, 2009 2:49 pm

sounds like unstable b+ or even flyback