Looking for info on memory

[Joshua Rice]

------ Original Message ------
From: "Nigel Johnson Ham via cctech" <cctech at classiccmp.org>
To: "Jerry Weiss via cctech" <cctech at classiccmp.org>
Sent: Thursday, 21 Oct, 2021 At 01:10
Subject: Re: Looking for info on memory
Thanks for that, but unfortunately it is crashing into ODT and not
accepting input from the console, which I remember was a symptom of no
bank 0 memory.
Now,of course, it could be the receiver chip in the J board (I used to
make a lot of money changing them ) but I have tried two separate J 
boards.
Of course if it is 4 MB, it must be in bank zero.
cheers,
Nigel



I've not had any experience with third-party Q-BUS modules, with nearly 
all my PDP-11's being built out of DEC cards, purely for the reason that 
documentation is easy to find. However, one thing i do remember reading 
up on is this: "NOTE WELL: For reasons which seem utterly 
incomprehensible, many boards designed for Q/CD slots (such as PMI 
<https://gunkies.org/wiki/Private_Memory_Interconnect>  cards) do not 
avoid the QBUS pins on the CD connectors which contain 'hazardous' (to 
TTL circuitry) voltages. Plugging such a card into a Q/Q backplane will 
generally destroy the card." https://gunkies.org/wiki/QBUS#Backplanes 
<https://gunkies.org/wiki/QBUS#Backplanes> .


Some of the later quad-height DEC memory modules had either jumpers or 
resistors/fuses/not-sure-what-they-are that could be snipped out to 
convert between Q/Q and Q/CD slots. I've seen this on MSV11-P cards. 
It's entirely possible that the card wasn't configured correctly, and at 
some point got fried by the mismatch between Q/CD and Q/Q.

I would definitely recommend obtaining another memory board and swap it 
in. Smaller capacity QBUS memory boards are usually quite cheap and 
plentiful, so getting a 64K/128k card isn't impossible and won't break 
the bank. It would at least help diagnose if it's the memory board, or 
if the issues are deeper seated in your backplane or CPU module.

I would also add, make sure your backplane is clean and not damaged. 
It's an easy thing to overlook, but corrosion, damaged traces, damaged 
pins, and general detritus can lead to all sorts of funky malfunctions.

Cheers

Josh Rice