Dead HP-97 calculator

From: Frank McConnell <fmc_at_reanimators.org>
Date: Wed Oct 1 10:04:26 1997

[Note: I saw Hans' message on comp.sys.hp.misc and replied
privately, but figure there might be some other folks here
who want to know this stuff.]

Hans Pufal <hans1_at_filan00.grenoble.hp.com> wrote:
> When I got it home I found that it rattled, so I dismantled it and found
> two large burnt out resistors on the keyboard PCB. The rattle was caused
> by pieces of these resistors in the case.
>
> Does anyone have docs sufficient to determine the replacement parts for
> these resistors?

Time for some copying from the service manual. Useful information below
is from the HP-97 Programmable Printing Calculator Service Manual,
HP part number 00097-90130, dated August 1976.

Table 4-9. Keyboard Printed-Circuit Assembly A2A1 (00097-60002)
            Replaceable Parts

Ref HP p/n Description

R1 0683-4715 RESISTOR, fxd, 470 ohm
R2* 0683-2045 RESISTOR, fxd, 200K
R2* 0684-3341 RESISTOR, fxd, 330K
R3 0812-0058 RESISTOR, fxd, 8.2 ohm, 2W
R4 0811-1674 RESISTOR, fxd, 4.7 ohm, 2W
R5 0698-8691 RESISTOR, fxd, 4.0 ohm, 1%
R6 0683-1835 RESISTOR, fxd, 18K, 5%, 1/4W
R7 0683-3915 RESISTOR, fxd, 390 ohm

CR1 1990-0450 LED, low battery indicator

Q1 1853-0393 TRANSISTOR, PNP
Q2 1853-0401 TRANSISTOR, PNP
Q3 1853-0374 TRANSISTOR, PNP
Q4 1854-0071 TRANSISTOR, NPN

U1 1820-1629 INTEGRATED CIRCUIT, cathode driver
U2 1990-0595 DISPLAY, numeric
U3, 4 1858-0044 INTEGRATED CIRCUIT, quad transistors

U5 1810-0252 INTEGRATED CIRCUIT, resistor network

P1, 2 1251-3955 CONNECTOR, 9-pin

W1 8120-2206 CABLE, 24-conductor

        00097-80002 BOARD, etched

R2 is marked with a * because it is selected based on the cathode
driver IC U1. I don't completely get this, but there is a chart
(Table 4-8, Cathode Driver Resistor Selection Chart):

        U1 Category: I J
        R2: 200K 330K

Given that you say the burned out resistors are "large" I am going to
guess that you are looking for R3 and R4.

Here's the layout toward the rear of the board if that helps.

            Q4 R7 R5
                Q2 R6
            Q3 R2
                 ---U5--- R1


             ---U4--- ---U3---
             -------- --------


                 ---U1---
                 --------


             -----------J1----------- Q1

                   R3 R4
                 
> What is the power input requirements for the HP-97?

12.8VAC (from paragraph 2-42).

Actually there is a flowchart that includes a test for the AC adapter.
For approximately 115VAC input, the output should be between
V(in)/10.55 and V(in)/7.82; for 230VAC input, the output should be
between V(in)/21.1 and V(in)/15.65. The next part of the test is
to connect a 10 Ohm +/- 5% 5W load across the output of the AC adapter
and measure the voltage across the load; it should be between 6.2 and
7.4VAC.

Hope this helps!

NB- I read your message in comp.sys.hp.misc. It looks like you might
have posted it to classiccmp too. I am a bit behind reading that. Feel
free to repost this there.

-Frank McConnell
Received on Wed Oct 01 1997 - 10:04:26 BST