WG4900 - Doesn't power up

orion3311

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Working on a WG4900. Problem is that it doesn't turn on, although the fuse is good. I *believe* the 130v line on the back of the board wasn't at 130v. Tried swapping the voltage regulator, still no go although I couldn't get a reading on that line before a bad storm blew in and I had to close up shop. (Watching some pretty incredible lightning at the moment)

Anyhow, one thing I did realize, is by accident, I plugged my cord into the wrong outlet and ran the monitor off direct power instead of isolated. Nothing happened. This tells me there's something on the AC end of things open. There's 6 main diodes, and looking at the monitor from the back, the 4 to the left of the varistor all read good, the 2 to the right of the varister seem to read the same either way, and on another one I'm working on, I saw different readings with them backwards, but not MUCH different. Not sure if this is normal or not. I'll have to check them out of the circuit I suppose.

Anyone have any ideas?

Jeff
 
Looks like those two questionable diodes are for the degauser, in this case it wasn't hooked up. Looking at the schematic and there really isn't much to this thing...wish it wasn't storming I'd go back and poke some more.
 
monitor

Usually when someone plugs it into ac direct it takes out bridge rectifier diodes or bridge and can work it into the hot and posible flyback. i have seen the fuse look good but check it with a meter.
 
So it not doing anything could indicate an open diode, bad (but looking good) fuse or something otherwise wrong in the main AC section.

The fuse looked good, I believe tested good and had AC juice past it. I guess the next step is to unsolder R601 and see if it produces 130v.
 
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