HP86B/HP85 PSU testing - where to start?

[Tony Duell]

> 
> Hi list,
> 
> You may remember the big stack of HP85s/HP86Bs I pulled from a
> dumpster a few months ago.
> 
> They've been stored away safely since then, and now I'd like to get
> started testing them so that I can get them sold. Tony recommended
> running the power supplies on a dummy load to make sure that none of
> them are duds. I have a handy bag of Big Resistors that I can make
> dummy loads out of, however, (in an 86B at least, I've not been into
> the 85s yet) there's a 10-conductor cable coming out of the PSU and
> I've no idea what sort of load it might want to see and on which pins.
> 
> Googling for the service manual hasn't been productive.

The HP86B service manual and a reverse engineered scheamtic (which 
includes PSU pinouts) is on http://www.hpmuseum.net . From what I 
remember, this PSU is happy with no load at all -- just pull the cable 
that links it to the logic board, power up, and check the output voltages 
wrt the ground pin on the connector.

The HP85 is a bit harder. The service manual is available on the MoHPC 
CD-ROM set (http://www.hpmuseum.org), but you have to buy that. It's not 
on hpmuseum.net. And because I have the manual, I didn't produce my own 
schematic for that one.

The other problem with the 85 is that the PSU is on the same board as the 
printer circuity, and it's hard to get to between the printer/tape drive 
asembly on the right and the monitor assembly on the left. Really, you 
need to pull the 40 pin custom printer controller chip from the PSU board 
before testing it (yes, it is socketed). 

The PSU/peinter PCB is connected to the logic PCB (under the keyboard) by 
2 bits of tapewire. You will need to swing the keyboard up (undo the 2 
screws on the bracket behind the keyboard) to get access to this. The 
connectiosn, according to the service manual, are : 

        Rear 
       J8  J9
 GndH --o  o-- +12H
Phi_2 --o  o-- +12H
 GndH --o  o-- Phi_1
Phi_21--o  o-- GndL
 GndL --o  o-- GndL
   +5 --o  o-- PWO4
   B7 --o  o-- GndL
 GndL --o  o-- B6
   B5 --o  o-- +6
  -12 --o  o-- B4
   B3 --o  o-- +12L
   +6 --o  o-- B2
   B1 --o  o-- +5
   -5 --o  o-- B0
  Rd/ --o  o-- GndL
  +32 --o  o-- Wr/
 LMA/ --o  o-- PSS

You can ignrore all siognals other than +12L, +12H, +6, +5, -5, -12 and 
+32 (which are the PSU outputs). The 2 groudns (GndH and GndL) are linked 
on the PSU board, as are the 2 +12V lines. The +32V line is ungegulated, 
so don't worry too much about that.

All the other signals are the system bus to the printer control chip.

Oh, one other trick. When removing the top on an HP85, pull off the 
tape drive eject button first. 

-tony