• Please review our updated Terms and Rules here

Digital PDP 11/05 in BK11-K mounting box

I was not planning to fix the G114 right yet, but I can compare and contrast with the working card, makes it a lot easier to pinpoint the failure (with or without a schematic).
 
Follow up...There was actually nothing wrong with the core RAM modules, G114 in particular, but I was getting a lot of weird address inhibit errors (lines staying on). Something did not seem right as I was getting identical failures with different cards, a statistical impossibility unless....

I figured out that if I put a piece of shielding behind the core memory H217D card that would solve all of my weird RAM inhibit problems. I have since been able to load BASIC via papertape and it now runs flawlessly. I am using only the first 8K of RAM so I can put something else in the remaining 8K available (H217D is non-parity 16K RAM).

I can fire it up, turn on the teletype boot DEC BASIC from 000 000 and get the READY prompt from a cold start. I made a nice video, but I had the sound off so I need to re-take it when I have the patience to sit through a half hour papertape load again. The benefit of the initial load is that you get to see the initialization questions the system asks when you first load BASIC into core
 
Last edited:
billdeg said:
I figured out that if I put a piece of shielding behind the core memory H217D card that would solve all of my weird RAM inhibit problems. I have since been able to load BASIC via papertape and it now runs flawlessly. I am using only the first 8K of RAM so I can put something else in the remaining 8K available (H217D is non-parity 16K RAM).
Click to expand...

Great news :->. While we're waiting for the telz-all video, could you be specific regarding:

1. "piece of shielding"
2. "behind"

Originally it seemed that you were trying to use an electrostatic shield wrapped 'round "everything", rather than a magnetic shield?

THX.
 
Yes "the bag" experiment. Not really wrapped around everything, but the way things are laid out on the backplane one could speculate to shield both the H217D from the G114, as well as the M7261. So, I just folded the bag over and between the two target areas. I probably don't need the shielding between the back of the M7261 and the front of the M930.

Here is a photo of the shielded computer component bag as described:
http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag2.jpg

It worked perfectly so I snipped the bag down to be the same height as the cards so it would look better and air would flow until I can get something better to use long-term.

Bill
 
billdeg said:
Yes "the bag" experiment. Not really wrapped around everything, but the way things are laid out on the backplane one could speculate to shield both the H217D from the G114, as well as the M7261. So, I just folded the bag over and between the two target areas. I probably don't need the shielding between the back of the M7261 and the front of the M930.l
Click to expand...

Thanks for the update. I don't understand why what is intended as electrostatic shielding would work in a situation where magnetic coupling would presumably be the problem. I wouldn't think that there would be enough effect compared to a good plane-conductor. Can't argue with success, 'tho. It looks like your bags are the metallized type? Ref: http://www.esdjournal.com/techpapr/ryne/esdbags.htm

Note that, aside from the magnetic shields used in the 8/e-f-m, DEC also included shields in the MF11 (and variants; up to 3x 8K stacks). They were placed between the stack module-sets, and not between specific module-pairs. The ED references "electromagnetic shield (1700021-02) required between slots 03 and 04, and slots 06 and 07 when optional memory segments are added. Shields are positioned in module sections C, D, E, and F and held in with module holders (1209856-0-021)".
 
https://www.youtube.com/embed/uepU_gTkMFY

This clip is for Mike W. who wanted to be able to isolate the sounds of a person typing at the ASR 33 Teletype. This video demonstrates the PDP 11/05 discussed in this thread and covers how to start BASIC already in core memory from a cold start, enter a BASIC program, edit it, and run it with output going to the Teletype printer.
 
pbirkel@gmail.com said:
Thanks for the update. I don't understand why what is intended as electrostatic shielding would work in a situation where magnetic coupling would presumably be the problem. I wouldn't think that there would be enough effect compared to a good plane-conductor. Can't argue with success, 'tho. It looks like your bags are the metallized type? Ref: http://www.esdjournal.com/techpapr/ryne/esdbags.htm

Note that, aside from the magnetic shields used in the 8/e-f-m, DEC also included shields in the MF11 (and variants; up to 3x 8K stacks). They were placed between the stack module-sets, and not between specific module-pairs. The ED references "electromagnetic shield (1700021-02) required between slots 03 and 04, and slots 06 and 07 when optional memory segments are added. Shields are positioned in module sections C, D, E, and F and held in with module holders (1209856-0-021)".
Click to expand...

Their is a single shield board used in the PDP-8efm (basically just a board with a full ground plane) that goes between the first core stack controller and the last of the digital boards. Note that this is an electrical/grounded shield plane, not any fancy magnetic shield. The board is just a copper plane which is a non-ferrous metal. The shielding goes both ways; The intent in the PDP-8efm is to shield the first board in the core array stack (the analog core drivers) from the 'noisy' digital boards (which in the PDP-8efm omnibus have no ground plane, just ground traces). So the shield is not so much to keep the core arrays from affecting other logic, but to keep all the noisy digital logic out of the sensitive analog core array circuits.

Don
 
AK6DN said:
So the shield is not so much to keep the core arrays from affecting other logic, but to keep all the noisy digital logic out of the sensitive analog core array circuits.
Click to expand...

Thanks Don. The case of the MF11 still seems baffling since it doesn't appear from the documentation that the shields were grounded, and we're talking about shielding between memory-units and not WRT digital-logic modules. The phrasing "electromagnetic shield (1700021-02)" is rather ambiguous. I wonder what (sorts of) good a big _ungrounded_ plane does? Particularly one that seems likely to have been copper.

(And logically extending, the current situation of an ungroundede metallized plastic sheet.)

Didn't the 8/a also do similar inserts to the MF11?
 
I have a Canon XF300 with light boxes, etc. I upload to youtube at HD 1900 w, which is the highest res youtube allows. I use Adobe Premier Elements 13 but otherwise this was a quick video that took maybe an hour and a half total.
b
 
You must log in or register to reply here.
Back
Top