Rescued: HP85, HP86B, 912x drives - score!

[Tony Duell]

> 
> Hi list,
> 
> I pulled the following from a skip (or dumpster as you North Americans
> would have it!):
> 
> http://img163.echo.cx/my.php?image=hp854qg.jpg (5 x HP85 computers)
> http://img263.echo.cx/my.php?image=hp86b4wy.jpg (3 x HP86B computers)
> http://img263.echo.cx/my.php?image=hpdrives8zh.jpg (5 x HP9121 dual
> drives, 1 x HP9122 dual drive)

Nice toys!

> 
> Is there anything specific to these machines I should check (aside
> from the obligatory stuff-from-a-dumpster drying-out period) before
> trying to power them on? I haven't got a monitor that will do the NTSC

Yes!

Firstly, sources of hardware info : 

The HP85A 'Assembly Level Service Manual' (which does contain scheamtics) 
is on the MoHPC CD-ROM set.

A reverse-engineered HP86B schematic (only) is on the HPCC schematics 
CD-ROM. I have also enocuntered an HP86B service manual on a web site 
somewhere.

I don't know of a source of the 9121/9122 scheamtics. I have the HP 
service docs for the former, it contains no full schematics. Schematics 
for the double-sided drive (both the FC9 and FC16 board versions) are on 
the HPCC schematics CD-ROM somewhere. The 9121 may well appear on a 
future version of the HPCC CD-ROM, but I don't have a 9122...

Now for what you should do....

I would really recomend checking the PSUs without the logic connected. In 
my experience these supplies are fine with no load. In the case of the 
86B, the PSU is a separate PCB linked to the logic board by a cable. 
Pinouts are in the HPCC schematic, or I can e-mail them to you. Getting 
inside the 86B is easy, it's just the #1 pozidriv screws on the bottom. 
I think you can get to the PSU without removing the screening cover over 
the logic, but anyway it's all pretty obvious.

The HP85 PSU is on the PSU/printer board. That's the board on the left 
side of the printer module, between the printer and the video monitor. 
It's not so easy to get to!. To rrmove the cover, pull off the tape drive 
eject bar, then remove the screws from the bottom, then lift off the 
case. The keyboard is hinged at the front, held down by 2 screws at the 
back, take those out.

To get to the PSU it's best to remove the video section. There are 2 of 
those infernl tapewires linking it to the CPU board (under the keyboard). 
Unplug those, disconnect the brightness pot (3 pin connector), remove 2 
screws and loosen the third, and take out the video chassis. Then 
disconnect the PSU/printer PCB from the logic board (2 more similar 
tapewires), remove the printer control IC (the 40 pin chip on the 
PSU/printer board) and put it in conductive foam. Now you can test the 
PSU without risk of damaging irreplaceable custom ICs.

When you reassemble the machine make sure you re-connect the brightness 
pot connector. The monitor circuit is somewhat unconventional in that the 
brightness control varies one of the CRT anode voltages (not the grid 
bias). With the pot disconnected, there's no discharge path for the 800V 
supply smoothing capacitor, which will nicely zap you when you do try to 
reconnect the pot. The service manual (see above) has a procedure for 
discharging the capacitor if you think it's necessary.

The 9121 PSU is on the same board as the logic, so AFAIK you can't test 
it without the logic connected :-(. It's a somewhat odd supply anyway -- 
the +5 and  +12V rails come from the mains transformer via linear 
regulators, a -ve bias supply for the FDC chip comes from a 
diode/capacitor chain clocked from a logic-level clock. Oh, and the fan 
is a capacitor-run motor run off the transformer secondary (the run 
capacitor is on the logic board).

Now for the thing you _must_ do. The 9122 disk drive mechanisms have a 
nasty problem. If the grease on the eject mechanism goes sticky (and it 
does), said mechanism doesn't latch up properly. The result is that the 
upper head catches in the disk shutter when you try to eject a disk. And 
the head gets ripped off. Then you're looking for a new head assembly!. 
The single-sided mechanisms in the 9121 don't have quite the same problem 
(only the felt pressure pad gets caught), but it doesn't hurt to regrease 
those as well.

The procedure for doing it is roughly as follows.

Remove the top cover from the 9122, take out the screws holding the 
drives in place, unplug the cables and take the drives out. Remove any 
remaining screws/brackets from the mouting holes (I don't think this 
applies to ther 9122)

Take out the 1 screw on the back and take off the drive cover. 

Take out the 3 screws on the bottom and remove the screening plate over 
the logic PCB. Free the stepper motor wiring at the back, and ease off 
the logic board. Unplug all the connectors from the board and set the 
board aside (in an anti-static bage).

Remove the 2 scres from the bottom near the front edge of the drive 
chassis. These hold the front panel in place which then comes off 
complete with the eject button and spring.

Back on top, remove the eject damper at the rear left corner (1 screw). 
Remove the 2 screws the fix the head load solenoid bracket to the 
chassis, the rear one holds the earth tag. Remove this bracket, feeding 
the wires through the chassis. Put a clean lens tissue or similar 
between the heads.

Underneath again, remove the 4 screws near the side of the drive chassis. 
The disk holder assembly is now free. Take it off.

Take off the E-circlips from the sides of the disk holder assmebly. Take 
it apart, noting the positions of the spacers, etc. Note that the spacers 
often are so well stuck to the shafts that they appear to be part of the 
shaft. They're not. Remove the springs from the levers on the side, clean 
all the parts with propan-2-ol and make sure all the levers turn freely. 
Very freely. 

Then all you have to do is put it together again. I think the 9121 drives 
are much the same.

This may sould like a lot of work (it acutally takes about 30 minutes per 
drive), but it sure beats having to align a replacement head assembly, 
even if you can get one.

-tony