PDP-11/10 repair started

Henk Gooijen henk.gooijen at hotmail.com
Sun Oct 4 13:49:57 CDT 2015

-----Oorspronkelijk bericht----- 
From: tony duell
Sent: Sunday, October 04, 2015 8:16 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: PDP-11/10 repair started

> Some corrections to my post regarding the console LED behavior.
> Voltage levels on the CPU backplane are still good whne the 2 CPU boards
> are installed in the backplane, but the processor is not responsive to
> the switches on the console panel.

It's been a long time since I've been inside an 11/10 (that will change soon 
as I fix
the one damaged  by the idiot removal men,..) but just to eliminate the 
check that ACLO and DCLO are solidly high.

On a system like this I would always start by looking at the microcode 
program counter.
What state(s) is it in? If it is sequencing through states, does the 
sequence make any sense?
Does anything happen when you press LOAD ADDR (say)?

Maybe start from one of the switches like LOAD ADDR and see if it is 
generating the right
signals on the processor board.


Oops, I forgot to mention a few other checks that I did ...
AC LO and DC LO are some 4.6V. Both have a 130 mV ripple, no spikes.
That seems OK to me.

As the console ribbon cable was disconnected, I also checked the toggle
switches (LOAD ADDR, EXAM, START, CONT, DEP) and the switches SW0~SW15
and HALT/EANBLE. In the OFF position the signal is 0.06V and in the ON
position I measured voltages between 4.5 and 4.6V. Toggles and switch
signals seems OK too.
I am fairly confident that the console itself is OK.

Thanks for the tip checking the microcode program counter. I hope to
get to that next weekend. Also, with the correct module on extenders
I will check what toggling LOAD ADDRS does signal-wise. Looking at
the console LEDs it does nothing :-/

- Henk 

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