Author Topic: HP 35665A Power Supply  (Read 424 times)

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Online Johnny10

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HP 35665A Power Supply
« on: October 17, 2019, 12:54:44 am »
Just received a HP 35665A with faulty power supply.

No power at all.
After watching Dave's HP 35660 Tear Down I believe he said no schematic available for power supply.

Just hoping someone on the forum may have more information.

Thanks
Tektronix TDS7104, DMM4050, HP 3561A, HP 35665, Tek 2465A, HP8903B, DSA602A, Tek 7854, 7834, HP3457A, Tek 575, 576, 577 Curve Tracers, Datron 4000, Datron 4000A, Fluke 181, uTracer, HP5335A, EIP534B 20GHz Frequency Counter, TrueTime Rubidium, Sencore LC102, Tek TG506, TG501, SG503, HP8568B
 

Offline wn1fju

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Re: HP 35665A Power Supply
« Reply #1 on: October 17, 2019, 01:56:40 am »
Don't have a schematic, but for what it's worth, I fixed my 35665A power supply solely by inspection.  In my case, the thing blew a fuse immediately
and was already drawing 2A when I supplied 8VAC into it via a Variac.  It's a bit of a pain to disassemble, but an ohmmeter showed shorts in the main
switching transistor, the driving transistor, three 1N4148s and three 5.6V Zeners.  Quite a bit of carnage, but all easily replaced, and it fixed the unit.

So open it up, look for burnt parts, shorted parts, the usual stuff.
 

Online Johnny10

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Re: HP 35665A Power Supply
« Reply #2 on: October 17, 2019, 02:44:35 am »
Yes, that is what I started doing.

So far found 3 bad Diodes.
Tektronix TDS7104, DMM4050, HP 3561A, HP 35665, Tek 2465A, HP8903B, DSA602A, Tek 7854, 7834, HP3457A, Tek 575, 576, 577 Curve Tracers, Datron 4000, Datron 4000A, Fluke 181, uTracer, HP5335A, EIP534B 20GHz Frequency Counter, TrueTime Rubidium, Sencore LC102, Tek TG506, TG501, SG503, HP8568B
 

Online Johnny10

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Re: HP 35665A Power Supply
« Reply #3 on: October 19, 2019, 01:40:20 pm »
I am going to have to do more investigation or just buy a new power supply.

TRW 095-10097


The AC line fuse has not blown on my unit. But
I am finding full 155VDC voltage on VCC pin of UC3842 IC and gate of Power transistor BUW12A, doubtful if much of anything is going to work in the future.

Tektronix TDS7104, DMM4050, HP 3561A, HP 35665, Tek 2465A, HP8903B, DSA602A, Tek 7854, 7834, HP3457A, Tek 575, 576, 577 Curve Tracers, Datron 4000, Datron 4000A, Fluke 181, uTracer, HP5335A, EIP534B 20GHz Frequency Counter, TrueTime Rubidium, Sencore LC102, Tek TG506, TG501, SG503, HP8568B
 

Offline vtp

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Re: HP 35665A Power Supply
« Reply #4 on: October 19, 2019, 05:17:13 pm »
Some years ago rebuilt this power supply from my 35665A.

I do not think there was a single good electrolytic in this. I have also at least partial schematics drawn somewhere but they are not in electronic format and likely to be scattered over several pages of notebook. I do remember that there was something interesting about the switching transistor(s), IIRC it was emitter switched BJT with a lower voltage MOSFET. Or some other not so common arrangement.

Will see if I can find my notes.
 

Online Johnny10

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Re: HP 35665A Power Supply
« Reply #5 on: October 19, 2019, 07:45:06 pm »
Thanks for your help.

I keep wanting to put this aside but I keep researching!!!
Let it GO !   :-)

I just picked this up Thursday.

Someone else has been in here before me.
« Last Edit: October 20, 2019, 07:50:44 pm by Johnny10 »
Tektronix TDS7104, DMM4050, HP 3561A, HP 35665, Tek 2465A, HP8903B, DSA602A, Tek 7854, 7834, HP3457A, Tek 575, 576, 577 Curve Tracers, Datron 4000, Datron 4000A, Fluke 181, uTracer, HP5335A, EIP534B 20GHz Frequency Counter, TrueTime Rubidium, Sencore LC102, Tek TG506, TG501, SG503, HP8568B
 

Offline dom0

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Re: HP 35665A Power Supply
« Reply #6 on: October 20, 2019, 05:24:41 pm »
Some years ago rebuilt this power supply from my 35665A.

I do not think there was a single good electrolytic in this. I have also at least partial schematics drawn somewhere but they are not in electronic format and likely to be scattered over several pages of notebook. I do remember that there was something interesting about the switching transistor(s), IIRC it was emitter switched BJT with a lower voltage MOSFET. Or some other not so common arrangement.

MOSFET+BJT cascode for switching was sometimes used in ye olde times to work around voltage limitations of old MOSFETs. Basically using the lower MOSFET as a fast switch and the upper BJT to keep the high voltage from the MOSFET. I believe this arrangement was even made in an integrated form for some time.
,
 

Online Johnny10

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Re: HP 35665A Power Supply
« Reply #7 on: October 20, 2019, 07:55:08 pm »
I have been tracing out one of the boards.

It is as you said, UC3842A Current Mode PWM IC to BUZ71A MOSFET driving BUW12A High Power Transistor.

Have a lot of blown diodes, MOSFET, Resistors.
 
Tektronix TDS7104, DMM4050, HP 3561A, HP 35665, Tek 2465A, HP8903B, DSA602A, Tek 7854, 7834, HP3457A, Tek 575, 576, 577 Curve Tracers, Datron 4000, Datron 4000A, Fluke 181, uTracer, HP5335A, EIP534B 20GHz Frequency Counter, TrueTime Rubidium, Sencore LC102, Tek TG506, TG501, SG503, HP8568B
 


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