Need help with HP-23A

[Richard Post]

Hi Janusz,

You've got a short circuit in there some place.  Your note implies 
that the transformer itself is OK and the power supply only blows 
fuses when the diodes are connected.  I am also assuming you have 
ruled out a bad connecting cable or a filament line short.

Check both sets of diodes for shorts (and their polarity if the 
supply has been worked on). A VOM can be used to check the unplugged 
unit for shorts or leakage to ground.

Use a variac and monitor the current draw as the voltage is SLOWLY 
increased.  A small wattage 120 volt lamp in series with the input 
can also be used to limit current for testing.  A shorted diode will 
show up very quickly even with just a few volts of AC input.  A bad 
electrolytic or grounded choke  also.

Check each connection to see if a terminal has been accidentally grounded.

I bought an HP-23 at an auction.  Turns out that it had likely NEVER 
worked.  One of the diodes was reversed in by the kit builder.  I am 
assuming it had  blown fuses each time it was switched on and the 
builder gave up.  Was a good purchase for me since the components 
were never used.

I assume you know that those caps can hold a lethal charge even with 
the unit unplugged. Discharge those caps.  Make sure the bleeders are 
doing their job.

Be careful. The HP-23 circuit is quite simple but if you have no 
experience with high voltage doubler supplies, find a local "Elmer" 
mentor.

73,

Rich

Boatanchor pix

<http://www.qsl.net/kb8tad>

At 8:13 PM -0400 5/13/05, Janusz Juryk wrote:
>Greetings all,
>
>Need help to solve a problem with a HP-23A power
>supply. A friend of mine is trying to figure out why
>the fuse blows when the HV secondary of the
>transformer is connected to the rectifiers and
>capacitors.
>Can anyone help out?
>
>Thanks
>
>Janusz  ve2zhp
>

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://listserv.tempe.gov/archives/HEATH.html