Nieman... a 25 and 27" problem

[lilshawn]

Hey Rick...

a 3M27SF that goes dead (black) when the screen goes bright. Unit stays on if the brightness is turned way down (1/2)...

3M25SF that blows it's fuse immediately when plugged in... any obvious parts to start with?


EDIT:

Found a shorted diode in the bridge rectifier of the 25" monitor. probably power surge related.

still working on the 27...e-mailed rick about it.

[lilshawn]

replaced all the caps in the 27"...still makes a weird noise when the picture is bright (buzzing shorting cap kind of sound.)

picture starts to squeeze in left and right sides and the B+ drops from 136 and bounces all over going as low as 114. turning the brightness/contrast down, the picture stabilizes perfectly and the volts stay rock solid.

i can't tell WTF the sound is coming from...poking around with a plastic tool, i cant get the sound to change. Chassis is dark (no arcing inside anything that i can see) it's not coming from anything on the flyback side of the chassis (its louder on the power supply side) which is why I thought caps.

[MonMotha]

If it has a SMPS for the primary power supplies, check that the transformer core hasn't come loose.  They'll make all sorts of funny noises if that happens.

[grantspain]

had a similar issue on another forum and suggested check the earth as maybe the static was building up too much

[lilshawn]

had a similar issue on another forum and suggested check the earth as maybe the static was building up too much

If it has a SMPS for the primary power supplies, check that the transformer core hasn't come loose.  They'll make all sorts of funny noises if that happens.

nothing like these... seems like some insulation someplace in the B+ is breaking down and causing the short, possibly inside the SMPS transformer. not sure. but the other modes where the B+ is consideribly less, there is no issue. (std res. 76 volts - fine and med.res. 100 volts - fine)

[MonMotha]

Check the diode(s) on the output of the SMPS.  If these go leaky, all sorts of weird things can happen during half of the switch cycle as the reverse voltages can actually be fairly high and higher at high load.

[lilshawn]

after speaking with Rick, i've come to the conclusion there might be something wrong with the SMPS transformer. I have sent this chassis to Niemen to have it looked at.

Once the chassis returns, i will post the issue and the fix. I will also put together a video of the issue for prosperity's sake.

[lilshawn]

well for the sake of ease, a new chassis has been returned to me. I haven't heard what the issue with the other chassis was. its possible it has stumped them as well. i have another monitor that has developed a similar issue.

i'll ask about it and see what's up.

i have some video of the issue that i'll upload when i get a chance.