Looking for info on memory

[Nigel Johnson Ham]

Thank you Josh, my next move will be to get a different memory.

Like you say, Even an MSV11DDD will help sort it out. I only need enough
to get into ODT, and maybe run some XXDP.  I have tried two CPUs and two
J boards, so it is either the memory of backplane!

cheers,

Nigel


On 2021-10-21 4:29 a.m., Joshua Rice via cctech wrote:
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>
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> ------ 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
>