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Looking for a replacement part for HP 721A

Paul Koretko All Messages By This Member #73414 I am trying to find a suitable substitute, or the specifications for the CR7, in an HP721A power supply. The HP part number is G-29A-3 I haven't found information on the web. Thanks a million for help on this.? The blue smoke came out of the diode, and I want to put it back in. TNX es? 73 Paul K WA0BAG
Dale H. Cook #73415 At 04:31 PM 2/8/2016, Paul K wrote: I am trying to find a suitable substitute, or the specifications for the CR7, in an HP721A power supply. Later production calls for an HP 1902-0190 7.5 volt +/- 5% Zener for CR7. The blue smoke came out of the diode, and I want to put it back in. You will very likely smoke the replacement unless you first determine and repair the cause of the diode failure. Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA
Bob Albert #73416 Looks like a 7V zener.? You can probably substitute a 6.8 or 7.5V unit, maybe 250 mW.? If you want to get close to 7V you can measure a few to see if you can find one close enough.? Not a critical part at all.? It carries about a half milliampere in the circuit.? Maybe something in the 1N45x series for instance. Bob On Monday, February 8, 2016 1:31 PM, "hglent@... [hp_agilent_equipment]" wrote: I am trying to find a suitable substitute, or the specifications for the CR7, in an HP721A power supply. The HP part number is G-29A-3 I haven't found information on the web. Thanks a million for help on this.? The blue smoke came out of the diode, and I want to put it back in. TNX es? 73 Paul K WA0BAG
Alan Melia All Messages By This Member #73419 Classic thinking Dale !.....zeners usually have a resistor in series to determine the current.....it must have taken excess current to smoke.........that generally can't come though the resistor (they normally go open not short) so where else could the excess current come from. Then apply a meter to check that theory. This is the most fun part of repairing stuff......oh yeah it can also be the most frustrating.! Stuff that jus'works is nice but boring :-)) Alan G3NYK toggle quoted message Show quoted text ----- Original Message ----- From: "'Dale H. Cook' bridgewaterma@... [hp_agilent_equipment]" <hp_agilent_equipment@...> To: <hp_agilent_equipment@...> Sent: Monday, February 08, 2016 10:20 PM Subject: Re: [hp_agilent_equipment] Looking for a replacement part for HP 721A At 04:31 PM 2/8/2016, Paul K wrote: I am trying to find a suitable substitute, or the specifications for the CR7, in an HP721A power supply. Later production calls for an HP 1902-0190 7.5 volt +/- 5% Zener for CR7. The blue smoke came out of the diode, and I want to put it back in. You will very likely smoke the replacement unless you first determine and repair the cause of the diode failure. Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA ------------------------------------ Posted by: "Dale H. Cook" <bridgewaterma@...> ------------------------------------ ------------------------------------ Yahoo Groups Links
Dale H. Cook #73420 At 08:04 PM 2/8/2016, Alan Melia wrote: .....it must have taken excess current to smoke.........that generally can't come though the resistor (they normally go open not short) so where else could the excess current come from. Precisely - I would look for a base-collector short in Q4. That would lower the current limiting resistance to about 560 ohms and increase the current through CR7 by a factor of about 40. Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA
Paul Koretko All Messages By This Member #73425 开云体育 Thanks a million! Yes, I found the smoke let'r outer!? It wont happen again. TNX es 73 -- Paul K. WA0BAG

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