Getting intermittent stuck bits with my pdp 11 non parity core stack. Without getting into a lot of detail, I noticed that something is causing the inhibit to fart high every so often, effecting address bits and to a lesser extent data bits. I have been doing a lot of research. My question.. aside from manuals and the tech docs does anyone have any anecdotal info, advice or test procedures related to DEC core RAM and intermittent stuck bits? Shielding tips? Bill Degnan twitter: billdeg vintagecomputer.net
On 11/26/2015 03:27 PM, william degnan via vcf-midatlantic wrote:
Getting intermittent stuck bits with my pdp 11 non parity core stack. Without getting into a lot of detail, I noticed that something is causing the inhibit to fart high every so often, effecting address bits and to a lesser extent data bits.
I have been doing a lot of research.
My question.. aside from manuals and the tech docs does anyone have any anecdotal info, advice or test procedures related to DEC core RAM and intermittent stuck bits? Shielding tips?
I haven't had to do much repair work on PDP-11 core, but on PDP-8 core I've found them to be somewhat sensitive to power supply voltage and cleanliness...Ripple creeping in has caused me the problems you're seeing on that PDP-11 core. The other thing I've had issues with is the temperature compensation circuit; an open thermistor has bitten me more than once. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
My question.. aside from manuals and the tech docs does anyone have any anecdotal info, advice or test procedures related to DEC core RAM and intermittent stuck bits? Shielding tips?
I haven't had to do much repair work on PDP-11 core, but on PDP-8 core I've found them to be somewhat sensitive to power supply voltage and cleanliness...Ripple creeping in has caused me the problems you're seeing on that PDP-11 core. The other thing I've had issues with is the temperature compensation circuit; an open thermistor has bitten me more than once.
-Dave
Thanks Dave. I only have failures of bits flipping on, I have never seen a bit erroneously flip to off. I have traded out all cards, no changes detected surprisingly. .. so your power supply ripple suggestion makes sense. B
Thanks Dave.
I only have failures of bits flipping on, I have never seen a bit erroneously flip to off.
I have traded out all cards, no changes detected surprisingly. .. so your power supply ripple suggestion makes sense.
B
Also see what shielding can do. This morning there were no errors after I turned the system from its side to a position flat on the table. -- Bill
Tell me on the electrical engineering bonehead scale 1-10 what you think of this shielding (w/ makeshift sielded bag): http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag1.jpg http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag2.jpg http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag3.jpg The bag ends folded over as they are shield between the back of the core and the inhibit board AND shielding between the back of the M7261 CPU card and the M930 bus terminator. I could cut the bag into two parts if anyone is concerned with air flow, but I bet it will still flow to the cards. Power on? Bill On Fri, Nov 27, 2015 at 11:12 AM, william degnan <billdegnan@gmail.com> wrote:
Thanks Dave.
I only have failures of bits flipping on, I have never seen a bit erroneously flip to off.
I have traded out all cards, no changes detected surprisingly. .. so your power supply ripple suggestion makes sense.
B
Also see what shielding can do. This morning there were no errors after I turned the system from its side to a position flat on the table.
-- Bill
-- Bill
On Fri, Nov 27, 2015 at 12:10 PM, william degnan <billdegnan@gmail.com> wrote:
Tell me on the electrical engineering bonehead scale 1-10 what you think of this shielding (w/ makeshift sielded bag):
http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag1.jpg http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag2.jpg http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag3.jpg
The bag ends folded over as they are shield between the back of the core and the inhibit board AND shielding between the back of the M7261 CPU card and the M930 bus terminator. I could cut the bag into two parts if anyone is concerned with air flow, but I bet it will still flow to the cards.
Power on?
Sorry, that first one should be http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag.jpg -- Bill
On Nov 27, 2015 12:34 PM, "william degnan" <billdegnan@gmail.com> wrote:
On Fri, Nov 27, 2015 at 12:10 PM, william degnan <billdegnan@gmail.com>
wrote:
Tell me on the electrical engineering bonehead scale 1-10 what you think
of this shielding (w/ makeshift sielded bag):
http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag1.jpg
http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag2.jpg
http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag3.jpg
The bag ends folded over as they are shield between the back of the core
and the inhibit board AND shielding between the back of the M7261 CPU card and the M930 bus terminator. I could cut the bag into two parts if anyone is concerned with air flow, but I bet it will still flow to the cards.
Power on?
Sorry, that first one should be http://vintagecomputer.net/digital/PDP11-05_BA11-K/RAM-CPU_shield-bag.jpg
-- Bill
Long story short, tried and it works. Loading paper tape basic now....
participants (2)
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Dave McGuire -
william degnan