HP-97 Power Supply

[Gordon Dyer]

I have just got an HP-97 but without power supply.

It has a battery pack fitted.

My HP-71 PSU plug fits and I know it needs ac like the 71 but is it the same voltage?

[Raymond Del Tondo]

Hi,

HP used the nearly the same standard wall adapter for many machines.

My HP-91 desktop calc came with an 82031A adapter,
some of my other machines came with the 82066B adapter.

They both have 8 volts output at 3VA alternating current,
so no difference from the electrical side.
However, the 82031A plug for the calc has a somewhat different housing, but both adapters fit and work with the HP-91. The 82031A won't fit into an HP 82161A, for example,
because the plug housing fits exactly to the HP-9x machines.

Regards,

Raymond

[Gordon Dyer]

Thanks for the help, it is as I suspected, but I wanted confirmation before switching it on!

However the HP-97 seems dead, so I opened it and tested the voltages the main power rails on the output of the regulator went down to zero when I switched the on switch.

Seems as if something is shorting the power rails. I will investigate further....

[Tony Duell]

The HP97 (certainly, maybe other Topcats too -- I know for a fact the 95C has this) has a circuit to load the AC adapter should the 'battery' voltage attempt to exceed the main +ve supply rail voltage. This is designed to protect the machine if the battery pack goes open-circuit, preventing the sort of damage that's all too common in Woodstocks.
If the DC-DC converter circuit fails (this is often due to a failure of the oscillator transisotor on the CPU board), then this circuit will attempt to pull the battery voltage down to zero. I've seen one draw over 1A from my bench PSU when this happened.
As others have mentioned, the HP97 service manual is on the MoHPC CD-ROMs. And my experience suggests a 2N3904 is a suitable transistor to use in the DC-DC converter.

[Gordon Dyer]

Thanks for the suggestions, I am investigating....

[David Smith]

The universal 82059 plug goes with the HP97, etc.

The HPMUSEUM CDROM set has the HP97 service manual. There are a few common HP97 power supply problems. The power supply is on the display circuit board. Most problems start with a fried power resistor and can cascade into failure of three or four transistors.

[Gordon Dyer]

I have an older set from last year without the HP-97 service manual, maybe I will have to invest in a new set...

Can you tell me the PSU spec from the service manual?
Photos I have seen show a much larger PSU than the HP-71 so maybe I need more power...