[Test-Equipment] HP 8640B Fuse Question

[Barry]

That's the thing.  The board is etched with "2A", the schematic and parts list both show "2A", but for whatever reason, the board had a 1.5A fuse in it (and it appeared to be a factory original).  I'm guessing an incorrectly-rated fuse fell in the bin and was inserted on the board with no one finding it (maybe even had a run of them - who knows).

The counter was acting up before the fuse was jumpered in and its symptoms remain unchanged.  I have more investigative work to do for that.

I would not doubt tired, leaky electrolytics abound in this as it is over 40 years old and I don't think they've been replaced.  I do intend to check on these as well.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
> To: "Discussion of Electronic Test Equipment" <test-equipment at mailman.qth.net>
> Sent: Thursday, February 5, 2015 11:40:33 AM
> Subject: Re: [Test-Equipment] HP 8640B Fuse Question
> 
> 
> On 2/4/2015 11:21 AM, Barry wrote:
> > Update:
> >
> > I placed a 2A fuse in series with my ammeter across the fuse test points
> > and the regulator board came alive.  The fan started working and the
> > generator is putting out a signal (modulation works, attenuator works,
> > controls are a bit sensitive, etc.).
> >
> > Ammeter reads about 1.55A so it it made sense why the 1.5A fuse blew.  I
> > wonder if it coasted along at something just under 1.5A and as various
> > components aged and the line voltage went up in general, it finally blew.
> >
> > Someone put a sticker on the inside that reads "KAPUT".  Sure was a pretty
> > easy fix for someone to give up on it.  Probably was not someone's
> > personal generator and they had no big reason to fix it.  Don't know.
> >
> > The counter isn't reflecting the generated frequency ("000100" or something
> > like that) so I have some work to do there, but at least most parts are
> > proven to work.
> >
> > Thanks for listening,
> > Barry - N4BUQ
> >
> >        Doesn't the handbook state the correct fuse size?  Usually line
> >        fuses are set to be about 1.5X to double the normal current to
> >        prevent blowing from inrush.  If a fuse of specified size blows
> >        there is a problem.  The counter not working properly may be a
> >        clue.  Check the power supplies carefully, it might point to a bad
> >        capacitor somewhere.
> 
> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
> 
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