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PDP-11/23 plus Bus Grant Jumpers

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Hjalmar

Experienced Member
Joined
Apr 28, 2022
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On a PDP-11/23 plus why would one cut the bus grant jumpers W1 and W2 on the CPU card?
Trying to bring one up with just the CPU and Memory card installed. After replacing the 26.66 MHz oscillator I now have activity on the chips on the CPU board. The Run light will come on momentarily when I cycle the restart switch. All of the red trouble LEDS stay on at the back of the board.
Jumper J10 was jumped to J11 and J15. J18 and 19 were jumped as well.

I'll have an USB to Serial adapter tomorrow so I can see the Console port.

Finally making a little progress.

Thanks for any insights or suggestions.

Todd
 
Last edited:
Hjalmar said:
On a PDP-11/23 plus why would one cut the bus grant jumpers W1 and W2 on the CPU card?
Click to expand...
The manual is likely on Bitsavers, but my guess is for Q/CD backplanes like the BA23 and BA123. PMI isn't the only thing that uses the CD pins - IIRC, the RLV21 uses it to send signals between its two boards.
 
I'm seeing some activity on the console port so hopefully after I get a USB adapter I'll know where I stand a bit better.

Thanks
 
Sounds like you have the KDF11-B with onboard SLUs, ROMs, etc. Be aware that if you have the serial port set up for halt on break, and you have the cable unplugged, it will just halt.

Terri Kennedy said:
The manual is likely on Bitsavers, but my guess is for Q/CD backplanes like the BA23 and BA123. PMI isn't the only thing that uses the CD pins - IIRC, the RLV21 uses it to send signals between its two boards.
Click to expand...

RLV11 does, yeah (RLV12 is single-board), and will be destroyed in a Q/Q backplane. I can't think of other non-PMI things offhand that use CD interconnect.
 
Got the serial adapter a few minutes ago and the machine seems to be alive. 128K and the commercial Instruction set. Next, I'll have to put power to the CDC hard drive and see if there is any hope of it still working. I'm not very hopeful after talking to the scrapper who took it out of the building. He let the whole computer drop down each step as it was coming out of the building. I do have a Q-bone if it doesn't work. will have to read up on how to install and use it.
 
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