G07 Chassis
Changing The Filter Cap

G07 B+ Filter Cap

by Bob Roberts

Here's another one of those things that I keep repeating myself on, so I figured as simple as it is to do, it still deserves a place here on the BBBB & it shouldn't take very long to do at all. I'm referring to changing the B+ filter capacitor (C904) on the Electrohome G07 chassis that so many ask about. Some of you know it too well, having met up with it during a cap kit job where the fuse F901 was blown, paying no heed to discharing it & ending up in a shocking experience :-( You might take note to always discharge it before attempting to work on the chassis just to be on the safe side. This cap filters the B+ voltage as it leaves the bridge rectifier and during normal operation bleeds off its charge via the components on the chassis when shut down. If your chassis has a short that causes F901 to blow, it isolates the cap giving it no discharge path to ground, so when you brush against it in removing the chassis..... surprise! You provide the path to ground for it to unload it's charge :-(

Sooo... let us say that the first step to changing this capacitor is, to be on the safe side and discharge it to ground! You can short the 2 center terminals together with a screwdriver blade or simply use a jumper with alligator clips to direct it to ground.

Unsolder the 4 terminals of the existing cap, which appear to form an arrow pointing down in the pic above left. If you look at the lower 3 terminals you'll see that they all solder into the same pad on the chassis bottom. The two outside terminals are actually stabalizers for the cap due to it's size.

Since we are going to be replacing this one with a new modern one, which is much smaller in physical size, we will not need to stabalize it. In fact, we won't be using any of these 4 holes for mounting the new cap, so go ahead & fill them in with solder & open up the 2 thru holes closest to the center. The new cap will be utilizing these holes maintaining the same polarity... negative to the top & positive to the lower pad that once held the stabalizers.

Hopefully, your completed project will look like the above pic. Yes... you won't be able to find a 600uf 200v cap, but the 680uf 200v cap of today will fill in nicely.

Happy Gaming...