[Heathkit] HP23A trouble

[sbjohnston at aol.com]

>Have not tested the xfmr yet (I need some
>bravery liquid before I do that, hi,hi).

You're probably kidding about the confidence fluid, but be careful - 
the voltages in the power supply can kill.

I would test the transformer by powering it temporarily through an 
incandescent light bulb.  In other words, put a light socket in series 
with the hot lead to the transformer and screw in an regular old light 
bulb.  If the transformer primary is shorted, the bulb will simply 
light at full brilliance.  If the primary is OK, the lamp's small 
series resistance will not make much difference, and it won't light 
much or at all.  Then you can measure the secondary voltages and see 
what you've got.  Nice safety measure.

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
---------------------------------------------------------
Radio is your best entertainment value.
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-----Original Message-----
From: Carl <km1h at jeremy.mv.com>
To: Dick KF4NS <kf4nsradio at verizon.net>; heathkit at mailman.qth.net
Sent: Fri, Oct 23, 2009 1:19 pm
Subject: Re: [Heathkit] HP23A trouble










Unless the diodes were mismarked or reversed they should work fine. 
OTOH, I
only use 1N5408's for just about everything due to their battleship 
surge
ratings and never had a failure. They are certainly cheap enough.

Id start by testing the xfmr with nothing attached to make sure there 
is no
damage. Then proceed with caution.

Carl
KM1H





----- Original Message -----
From: "Dick KF4NS" <kf4nsradio at verizon.net>
To: <heathkit at mailman.qth.net>
Sent: Friday, October 23, 2009 2:04 PM
Subject: [Heathkit] HP23A trouble


>I recently replaced the diodes with 1N4007's and all was
> fine......until yesterday. I fired it up with no load to record the
> voltages and heard a loud pop. The breaker was tripped so far that it
> reversed the spring contacts so would not reset. I opened it up and
> popped the contacts back to the opposite position and tried again. I
> did the usual visual inspection and the "initial tests" before trying
> again. It tripped again so did my diagnostics and found all the new
> diodes shorted.
>
> I realize that 1N4007's are rated at 1000V PRV but only at 1A. The
> breaker is rated at 2.92A. Is there a preferred sub for the original
> Heathkit diodes? The 125mfd caps are testing ok except C3 at 159mfd
> and C4 is 115mfd. None are shorted.
>
> Have not tested the xfmr yet (I need some bravery liquid before I do
> that, hi,hi). The breaker will be replaced with a slo-blow 3A ceramic
> fuse and should be ok along with an ICL in the power lead.
>
> By the way, anybody have 4 100K 2W to sell me? The existing 10pct.ones
> are all out of tolerance.
>
> 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!
>
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