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HP Forum Archive 05

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HP 85B Power Supply Question
Message #1 Posted by Michael (Texas) on 6 Feb 2001, 9:33 p.m.

I recently purchased a surplus HP 85B that apparently had been modified to operate at 48V. In fact the warning on the side of the machine states: "CAUTION - THIS UNIT HAS BEEN MODIFIED FOR 48V OPERATION GND=_12V ON RELAYS AND MODEM". The machine has MCI property tags on it. I guess my questions are:

a) has anyone ever run across a similarly modified 85B?

b) does anyone have a power supply wiring diagram for the 85B or a service manual?

c) could the existing power supply have been modified to run on 48V (or ~60V) without replacing the transformer (maybe bridging a phase on the 220V input tap?? - please excuse my ignorance of electronics design if that statement happens to be preposterous)?

d) what could be meant by the second part of the warning "GND=_12V ON RELAYS AND MODEM"?

e) what should the transformer output tap voltages be (it does appear to have two output taps - I guess one for the CRT and one for the other circuitry)?

Any help would be greatly appreciated.

Re: HP 85B Power Supply Question
Message #2 Posted by Andrés C. Rodríguez (Argentina) on 7 Feb 2001, 7:12 p.m.,
in response to message #1 by Michael (Texas)

Some equipment used by telecommunications companies is adapted to run with 48 V DC, so to simplify the use of batteries as a backup power source. It may be your case, if so, please note that it is DC, no AC !!

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