New Hp9100A owner needs some repair help..

[jdreesen]

Short intro, as this is my first post here :
Jos Dreesen, from Switzerland, long time classic computer collector.

First "contact" with HP calcs : pressing my nose against a german shopwindow and longing for those jewels, totally out of reach for a 12 year old's pocketmoney. Hp35 ? 25 ? Don't remember..

Heavy HP41 user several years later.

Now retired, and stumbled upon a good find :
A HP9100A in very fine nick.
....with the memory expansion...and a printer....and a plotter....plenty magcards & full doku...

Allas marred by the fact that it does not work.

Checked so far : powersupplies OK, clocks ok. No display, internal statemachine ( ctl board with threader core rom ) does not seem to run..Where to start ? Tony had some suggestions that I will follow on, but happy to accept ideas from other s !

BR Jos

[Roland57]

Jerry Walker posted a series of wonderful repair-videos on youtube. Just google for "Jerry Walker hp9100 repair part1"

Roland

[cruff]

(11-09-2022 08:20 PM)Roland57 Wrote:  Jerry Walker posted a series of wonderful repair-videos on youtube. Just google for "Jerry Walker hp9100 repair part1"

Indeed, this video series is a "much watch" before you start working on your 9100.

[trevor]

Stating your experience with electronic circuit repair helps us to
guide you...

To determine if the problem is in the Display or in the Logic:

See if there is any hint of green glow from CRT in dark room.
Turn on power, wait a minute, then turn off. Any green light
from CRT?

A common Display failure is the HV transistor Q1 and/or CR1,
see the Service Manual. Also the output transistors in the
Horizontal and Vertical boards. Before removing these two boards,
be sure to disconnect the four leads that go between the boards and
the CRT neck. The leads must be gently pulled off the radial CRT
deflection plate pins.


If the logic circuit is OK, pressing clear, clear, 1, change sign, square root,
should make the error light illuminate. Note however, the error light is
an incandescent bulb, so check that the bulb is OK.



Carefully unplug each of the five circuit boards and clean the gold edge
connector fingers with an Isopropyl Alcohol saturated paper towel.
Do not use abrasives. Carefully reinstall.


Consider removing the Card Reader temporarily....the Calculator will work
without it.

Trevor