[volt-nuts] 3458A AC board

[Randy Scott]

Greg,

Thanks for the information.  However, it was actually F701 (my bad) that was blown.  Taking a chance, I jumpered it to one of the spares and it seems to be running great.  It seems too easy... :)

Randy.


--- On Wed, 8/26/09, Greg Burnett <gbusg at comcast.net> wrote:

> From: Greg Burnett <gbusg at comcast.net>
> Subject: Re: [volt-nuts] 3458A AC board
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Date: Wednesday, August 26, 2009, 11:24 AM
> Randy wrote:
> There are two soldered-on fuses on the AC board: F701 seems
> okay (ohm meter 
> sees a short), F702 is open (blown).  Anyone have an
> idea what this fuse is 
> for?
> --------clip--------
> 
> Randy, F702 is a 0.125A fuse between raw -18V and the
> collector of Q702, 
> which is the -17V regulator. So I'd first measure the
> resistance from board 
> ground to the emitter of Q702. It it's a short (or nearly
> so), you'd want to 
> follow the -17V line to see what's holding it down. First
> thing to look at 
> would be the 15uF capacitor (C709) running from the emitter
> of Q702 to 
> ground.
> 
> F001, F002 and F003 are indeed spare fuses, so you can use
> one of them to 
> replace F702.
> 
> Let us know what you find.
> 
> Greg
> 
> 
> 
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