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Re: [Amateur-repairs] FT-736 Power Supply



Ed et al,

Thanks for your comments.  The hash is now about 10 mv p-p which is I think
good for a switcher. The power supply now appears to be working normally.
The hash appeared to me random noise on my scope.

The failure appeared to develop slowly.  Anyway, thanks again.  I'll keep an
eye on it and see what happens.

73 de Ken - K5GUU
Amsat-NA LM #1565

----- Original Message ----- 
From: <ma.locksmith@juno.com>
To: <kgshutt@cox.net>
Sent: Sunday, November 02, 2003 10:46 AM
Subject: Re: [Amateur-repairs] FT-736 Power Supply


> I assume you mean R17 and R18 for the 33 ohm resistors?  Yes, I'd solder
> them up again.  Anything that has a poor connection can create hash.
> Look at all high current connections including the transformer windings.
> I'd solder each just to be sure.  A bad connection does not necessarily
> look bad.
>
> I see this is a "brute force" switcher in that it does not use a chip for
> control.  They are a little easier to troubleshoot.  I'd first suggest
> soldering around L21 and the two resistors.  This is the current shunt.
>
> If you have a scope, I'd look to see what waveform the hash exhibits.
> Then maybe it will point to the source.
>
> I have to assume this is something that happened suddenly?  Or slowly
> came about?  But, in any case, it was not there when the supply was new.
>
> Ed
>
>
> On Sat, 1 Nov 2003 21:08:33 -0600 "kgshutt" <kgshutt@cox.net> writes:
> > Ed,
> >
> > Thanks for your reply.  A copy of the schematic in pdf format is
> > attached.  The resistors in the blackened area are R18 and R19.  The
> > schematic shows them as 33 ohms not 100 ohms (my mistake).  One of
> > these seemed loose and I resoldered it.  The ohter power resistors
> > are R8 and R9.  These are the 100 ohm resistors.
> >
> > The problem with the supply was excessive hash.  Several volts as I
> > recall.  I'll take some measurements and let you know whats going
> > on.
> >
> > Thanks again,
> >
> > Ken - K5GUU
>
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