-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Tuesday, 30 March 1999 6:43
Subject: Re: Decwriter II
The paper out logic is pretty simple. The output of the
switches goes
through a little RC circuit to the input of a 7474 d-type (unfortunately
which chip this is depends on the board version - it's E5b on an M7723
and E34b on an M7728). The output of that ff is the ready line.
marvin was kind enough to post similar data. Looking at that area this
afternoon.
It appears that the switch is closed when the printer
is out of paper. So
my first test would be to find the 100 Ohm resistor between the D-input
of that chip (pin 12) and pin BB on the keyboard connector. Unsolder it.
This disconnects all the switches. Does it work now?
No.
I don't, alas, have the schematic of the chassis.
But it appears from a
general wiring diagram that the paper out switch is in parallel with the
cover interlock switch. Have you checked that one?
Yes. the switches are not implicated. I disconnected the whole switch
assembly, still no go. Stuck output on the chip I'll bet, the fact it was
intermittent for a while makes a logic chip failure even more likely. (I
don't think I mentioned that earlier)
Thanks for your help......
Cheer
Geoff Roberts