Herb's DEC PDP-11/34

This page Last updated July 20 2017; epilog Aug 31 2024. My other DEC stuff is on this linked Web page. To email me, see see my ordering Web page for my email addresses.

I acquired this PDP 11/34 and two RL01 drives in July 2011. They were in a DEC rack but I did not acquire the rack. The system was powered up but not tested in 2011. I've not had an opportunity to work on the system since pickup. But in early 2017, I loaned the system to Jonathan Chapman for his Unibus testing. He made great progress on powering and testing the 11/34 chassis and board set. With a few more boards from me, it's now working (the RL02's are not tested) as of April 2017. In 2024, I sold the system and the new owner restored the RL02's, and will likely restore the 11/34. - Herb

My PDP-11/34

PDP-11/34 case view from the top. In this top inside view of my PDP 11/34, you can see I have a set of backplanes of over 20 slots. The front panel is to the left.

Cards in my 11/34, front to back (right to left), are

M?? - programmer's console (octal display and switches)
M8266 - KD11-EA PDP11/34A CPU control UNIBUS module
M9312 Bootstrap Terminator Board 
M7859 - PDP11 KY11-LB CONSOLE INTERFACE
M7891 (two) 128K x18 MOS Memory PDP 11 UNIBUS
M9302 PDP11 Unibus Terminator card
plus numerous bus-grant cards.

Cards not in the chassis but acquired in addition are: 
M7856 DL11-W SERIAL LINE UNIT (SLU) and REAL-TIME CLOCK 
G7273 grant continuity card
M9203 DEC UNIBUS BACKPLANE CONNECTOR
M7762 RL11 UNIBUS RL01/RL02 disk controller

There's a now-empty backplane of nine slots. The M9203 bridges the two backplanes. The M7762 RL11 controller for the RL01 has a IDC flatcable connector to the RL01 data/control cable.

A photo of the Unibus card map on the chassis shows this chassis was first configured in May 1986.The serial number nameplate shows this was an 11/34A and a number AG319XX.

RL01 hard drives

I also acquired two RL01 drives. Also, a disk pack. Later in 2013, I picked up three RL01 packs.

Repairs in 2017

The system and drives were acquired in July 2011. They were in a DEC rack but I did not acquire the rack. The system was powered up but not tested prior. I didn't have an opportunity to work on the system since pickup. In late 2016, I made arrangements with Jonathan Chapman to pick up and work on this system. He completed tests and repairs, using additional boards I supplied, and got an 11/34 set of boards running on one of the two backplanes. You can see more of Jonathan's vintage computing work on his Web site. Here's what he did for my system; I'm very greatful. - Herb

In early March 2017, he got the 11/34 chassis on the bench and powered it up - then found a mouse nest in the power supply, and took time to remove it. He reported later: ".. the power supply issue was a dead capacitor in the power control board. It was causing the main cut-in relay to just buzz, which is why not even the fans were coming on. I guess it closed once on the first test and then the capacitor let go.

Since I had it open, I cleaned all of the regulator modules, and replaced two blown incandescent indicators on the secondary +5 supply and the ± 15V supply. I powered them up with a few automotive tail lamps as a dummy load and adjusted the rails.

It sort of powered up with your board set installed. Apparently someone installed the ribbon upside-down on the programmer's console, which fortunately won't hurt anything. Seems that your control board and KY11-LB are not functional. My board set appears to work fine [in your chassis], after re-addressing the RAM. The lower portion of your RAM, up to the boot ROMs at octal 160000, seems to work, but I'll load an XXDP exerciser and find out for sure.- Jonathan

Later: General update on progress: I strapped up a spare DL11 I've got for my PDP-11/10 as SLU 0, which is where a TU58 generally sits. This morning I loaded XXDP tape images via tu58em, a PC-based [serial] TU58 emulator. My CPU boards [in your chassis] passed XXDP 11/34 CPU and memory management diagnostics, your RAM boards pass MS11 tests. ... Your Bootstrap/Terminator works fine, and has a ROM for booting DD devices (like the TU58) so I didn't even have to toggle in a bootstrap loader. I set up the board for no autoboot since I've been using [my card set's] programmer's console extensively. You can of course hit CTRL + BOOT on the console to jump into it.

It appears that there is a problem with the second backplane and/or the Unibus jumper. All of my Unibus jumpers are the old, short 11/05 style that won't work with the 11/34 card guides, or I'd try another. The second backplane was dirty, it got a bath and spent an hour in the hot air drying cabinet. No improvement. When it's connected, it behaves like a NPG jumper is missing (can't halt CPU, hitting CTRL + HLT on the console gives BUS ERR). I checked and all NPG jumpers are installed -- I rewrapped two that looked poorly wrapped, and checked the grant line all the way through and back out with my Simpson 260 meter. Note: Jonathan never got the second backplane to work, despite trying many Unibus jumpers. - Herb

Mar 22nd: I sent an additional set of boards to cover the nonworking ones. - Herb

Problem [with Herb's CPU board] solved, bad 74LS00, physically damaged it looks. Your CPU now passes the XXDP 11/34 tests. I assume [the chip] was in the bus grant circuitry since the programmer's console couldn't halt it.

I tested the rest of the boards you sent today:

KY11-LB - works fine, currently installed [with my programmer's panel]
DL11 - strapped up for RS-232, 9600 baud, SLU0, works fine
RL11 #1 - marked as having come from the 11/34, machine won't halt/boot with it installed
RL11 #2 - question mark on handle, fails controller tests, bad bits in some of the registers
RL11 #3 - works, standard CSR and vector, BR #5, passes VRLBC0
M9312 - works, set for no autoboot, has console emulator and RL boot ROM
Unibus terminator - replaced three badly broken ceramic capacitors, works
MDB DL11-W workalike - can't find documentation, can't test without it

Jonathan also tested and repaired a few bus extender cards I sent him. - Herb

So, we've got you together a working 11/34a board set, complete with console SLU, SLU0 for TU58 booting/emulation, 128 KW RAM, and a RL11. I've got the RL11 out of it at the moment since I have no drives to use it with. You can place the green bus grant + DMA card in the slot and run without it, which is how I currently have it configured. Everything I've tested, aside from the boards currently installed in the chassis, has been labeled with the tags you provided.

Your DL11 required some surgery -- one of the baud select rotary switches was really chewed up and couldn't be turned with a screwdriver. I desoldered it, but I don't have a replacement, so I jumpered the center pins of the two rotary switches together. There's a convenient pair of pads that allow for this. That means that receive baud == transmit baud, and you use the one remaining rotary switch to select it. I figured most people always use the same two baudrates anyhow. - Jonathan Chapman

Q & A

How difficult was it to extract the IC from the CPU board?

Not difficult, I did the usual, "cut the legs off and extract them one at a time, then clear the holes." I've got a Hakko 472D vacuum desoldering station, but DEC uses such small annular rings on their plated through holes that even with the proper tools I almost always end up lifting a pad/trace.

Any clues about the failed [KY11-LB] unit?

I suspect that the problem is in the Unibus control circuitry, since the front panel does display and tries to respond to keypresses. Probably something in how it does NPG.

And the other RL11's?

...Likely just a bad latch or bus tranceiver.

RL01 hard drives restored in 2024

Copyright © 2024 Herb Johnson