need PDP-11 restoration assistance

[MattCarp]

I'm looking for some help getting my PDP-11 to boot. I've tried usenet a couple times a while ago, but no luck. My replies were like "it should just work".

I have a MicroPDP-11/73. When attempting to boot an XXDP floppy, I get an "Error 20, Controller Error".

I've taken all of the boards out of my PDP except for the processor, memory, and disk controller (RQDX3). I've removed the hard disk from my machine and have only an RX50-AA plugged in.

When I do a "BOOT DU0" from the monitor, the RX50 doesn't even spin. However, I believe the drive works, because I was able to plug it into an old PC and it appeared to operate just like any other disk drive.

I've confirmed the RQDX3 jumpers are set to factory defaults.

I've received the same behavior from two different RQDX3's. Two controllers couldn't possibly be bad?

Does anyone have experience with this type of error? Alternately, if you have a PDP-11/73 up and running, I'd be willing to send components to you for verification. Heck, there's only 8 parts - power supply, system backplane, disk distribution panel, CPU, memory, controller, drive, front control panel. If I could isolate the problem, I could fix it!

[dr.emiel]

Contact the guys from www.classiccmp.org.
Or http://www.pdp-11.nl/ this persoon.

Dr.E

[tradde]

I'm looking for some help getting my PDP-11 to boot. I've tried usenet a couple times a while ago, but no luck. My replies were like "it should just work".

I have a MicroPDP-11/73. When attempting to boot an XXDP floppy, I get an "Error 20, Controller Error".

I've taken all of the boards out of my PDP except for the processor, memory, and disk controller (RQDX3). I've removed the hard disk from my machine and have only an RX50-AA plugged in.

When I do a "BOOT DU0" from the monitor, the RX50 doesn't even spin. However, I believe the drive works, because I was able to plug it into an old PC and it appeared to operate just like any other disk drive.

I've confirmed the RQDX3 jumpers are set to factory defaults.

I've received the same behavior from two different RQDX3's. Two controllers couldn't possibly be bad?

Does anyone have experience with this type of error? Alternately, if you have a PDP-11/73 up and running, I'd be willing to send components to you for verification. Heck, there's only 8 parts - power supply, system backplane, disk distribution panel, CPU, memory, controller, drive, front control panel. If I could isolate the problem, I could fix it!


I have no 11/73 nor have I worked with one. I do have other 11s. It does
seem odd that both controllers don't work. I am pretty sure error 20 means
the system is not seeing the controller. At least on my 11/84 it means
that. Is the 73 Q-bus or Unibus based? Do you have those little NPG
cards in all unused slots? I am guessing they are still needed here.
Maybe clean the contacts on the board?

[ericj]

Have you tried "boot du1"? I don't know if the controller remaps the floppy to du0 when there's no hard drive.

[ericj]

Also, which slot is the RQDX3 installed in and what backplane/chassis to you have? If all you have in the chassis are the cpu and memory card(s), the RQDX3 will need to be in the next slot following the last memory card.

[tradde]

Did you ever fix this problem, or make any progress on it?

[MattCarp]

Ok - this only took a little over two years, but I did fix my PDP-11/73.

It turns out the problem was an INCORRECT 50-pin cable from the controller to the signal distribution board.

I pieced the system together and the 50-pin cable had both of the connectors (ribbon cable IDC connectors) on the same side of the cable. This had the effect of swapping the signals from the top row and putting them on the bottom & vice versa. I didn't catch it the first time because the cable tested ok - no shorts or breaks.

Anyway, now I'm able to spin the RX50. I made an XXDP boot disk with PUTR & the simh PDP-11 emulator. Unfortunately, I get an "Error 21, Drive Error".

I believe this is due to a bad RX50, so I bought a replacement drive. It should be here in about a week.

stay tuned!