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Author Topic: HP-23 Power Supply  (Read 583 times)
KE4TSG
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Posts: 2




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« on: August 15, 2004, 03:03:10 AM »

I recently obtained an SB 101 with the HP-23 Power Supply.  I connected them together and when I started them it was ok. After a couple of seconds I smelled burning coming from the power supply. By the time I went to shut it down it went dead.  I looked around and felt around and the only thing I could feel was that one of the black 450V capacitors was hot and the others weren't. Is that what probably got burnt? What would I replace it with today?
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KA5N
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Posts: 4380




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« Reply #1 on: August 15, 2004, 02:43:23 PM »

Hi Juan,
First the HP-23 power supply is close to 40 years old and the electrolytic capacitors could all be bad.  The first thing to do is disconnect the power supply and check all the silicon diodes for shorts and then check all the electrolytics for shorts.  If you have a short the circuit breaker has probably tripped.  If you smelled something burning it could be inside the SB-101.  If electrolytics short they often outgas a sort of chemical smokey smell.  If a didode shorts it can then cause an electrolytic to short.  The diodes are no problem 1N4007 rectifiers (about 10 cents each from Digi-key and Mouser) the electrolytic capacitors are a bit more difficult as todays componets are usually a different form factor than older units.  C1 and C2 are 125ufd @450 volts are the most likely to be bad and it may be difficult to find caps with this value that mount the same way.  D1, D2, D3, D4 are probably 1 amp 400 volt units and the pairs D1 and D2, and D3, D4 can be replaced with a single 1N4007 (a 1 amp 1000 volt unit).
You may want to get help with repairs if you are not experienced with troubleshooting asn lethal voltages are present in the power supply and the SB-101.
When repairs are complete you will have to reset the circuit breaker by pushing in the red button and releasing it.
Good Luck Allen
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KE4TSG
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« Reply #2 on: August 22, 2004, 09:34:36 PM »

Thanks for the advice. I spent about a week reading about electronics and went into the power supply very carefully. I found that D6 was shorted out.  I replaced it and it is working like a charm.  All the voltages are Ok and I am contemplating replacing the old capacitors for new ones.
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W9GB
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Posts: 2475




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« Reply #3 on: August 29, 2004, 02:36:40 PM »

Juan -

There are a number of Internet web sites (Google search) with additional information on rebuilding HP-23 power supplies.
Here is schematic and operational description:
http://www.theheathkitshop.com/hp23.html

Repalcement electrolytic capacitors for the HP-23 are available from a number of sources.  
The best prices for electrolytic capacitors are found at Mouser Electronics.  www.mouser.com  You can order by phone or Internet - very helpful staff.

You can also look at The HeathKit Shop and Mike Bryce's repalcment PC baord design (this was featured in a past QST article)
http://www.theheathkitshop.com/hp23r.html

w9gb
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AC7CW
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Posts: 200




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« Reply #4 on: October 14, 2004, 09:36:51 PM »

I have heard of rebuilders taking the old cap out and rebuilding it by gutting it and putting a newer smaller cap inside it, same or better electrical specification is in order of course and easy to find in a smaller size than the original for sure.

Max
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NS6Y_
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« Reply #5 on: March 24, 2005, 11:38:57 PM »

I knew a guy who was into buying and restoring old radios and the first thing he'd do is "recap" them, IE, replace all those old electrolytics and I think other critical caps too.
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