VAX 11/750

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VAX 11/750
Gone, but not forgotten
Hardware
Vendor:	Digital Equipment Corporation
Model:	VAX 11/750
CPU:	VAX 11/750 (LSI)@6MHz
RAM:	8MB
Software
OS:	None
Collection Data
Acquired:	2003
From:	Arclight; Albuquerque, NM
Paid:	$0
Relinquished:	2004
Relinquished to:	Rawson Self Storage Auction
Catalog Data
Location:	Location Unknown
Usage Info
Role:	Restoration Attempt

Summary

Found this machine in 2003 while posting for one in the CCTalk mailing list. Arclight, a vintage computer dealer from Albuquerque, NM, offered me this one free of charge. It had been sitting in a barn in Mountainair, NM since approximately 1985.

I picked it up in my mother's 1996 Chrysler Town & Country minivan, and brought it home. Most of the details of the restoration project are below, but missing from it is the part where Jonathan Macmillan got his engineering students to desolder the 1489 RS-232 line driver on it and replace it with a socketed replacement, as the original was blown (a problem common to these computers) and would output, but take no input.

By the time I received the repaired board, the machine was already in the Pecos Self-Storage Unit. Before I could try out the new board, the Storage Unit Tragedy of 2004 occurred, so the machine never got a chance to experience the second chance it really deserved.

I had a pair of RA70 drives (with no housing) ready for this machine, and a chance to pick up a free TU-81+ drive from Austin, TX.

Restoration Project

This section is for an old restoration project for a computer I no longer own, and is presented here for its historical relevance.

Picking up the Goods

27 October 2003

Drove to Albuquerque. This VAX had been sitting in a damp shed in Mountainair, New Mexico for a decade. The fellow I got it from was most accommodating and had lots of extras and info to offer. I'll definitely be going to him for future needs. He hooked me up with a case of TU58 tapes, a DELUA, and was generally great to work with. Anyway, it was on the back of his dually pickup and we hefted it into a borrowed minivan.

Got it home. Talk about dirty! Mice had been using the VAX as a shelter, and they had left copious amounts of evidence. All over the unit. Also, plenty of very sinister looking spiders had taken up residence in the cardcage. Time for a shower and rest!

The box is a fairly basic configuration, with no FPA, 8MB RAM. I'd like to equip it with an L0001 FPA, a UDA50 SDI controller, a TU8x tape drive and controller, some disks (either SDI or Massbus), and a copy of VMS. Once I get it working, anyway...

Card Configuration

Slot	Card	Description
1		OPEN
2	L0002-E	Data Path Module (DPM)
3	L0003-K3	Memory Interconnect (MIC)
4	L0004-N2	Unibus Interconnect (UBI)
5	L0008-YA	Patchable Control Store (PCS)
6		OPEN
7		OPEN
8	L0007-B	Massbus Adapter (MBA)
9		OPEN
10	L0016	Memory Controller
11	M8750-CF	1MB ECC MOS Memory
12	M8750-CP	1MB ECC MOS Memory
13	M8750-CP	1MB ECC MOS Memory
14	M8750-CJ*	1MB ECC MOS Memory
15	M8750-CJ*	1MB ECC MOS Memory
16	M8750-CJ	1MB ECC MOS Memory
17	M8750-CJ*	1MB ECC MOS Memory
18	M8750-CP	1MB ECC MOS Memory
19	M9202	Unibus Connector
20	M9202+FLIP CHIP(2)	Unibus Connector
21	G7273	NPG and Bus Grant/Continuity
22	G7273	NPG and Bus Grant/Continuity
23		OPEN
24	G7273	NPG and Bus Grant/Continuity
25	G7273	NPG and Bus Grant/Continuity
26	G7273	NPG and Bus Grant/Continuity
27	G7273	NPG and Bus Grant/Continuity
28	M9313+FIL CHIP (2)	Unibus Exercisor/Terminator

(2) FLIP CHIP GRANT CONTINUITY CARD INSTALLED 3RD SLOT FROM BOTTOM

Dismantling

28 October 2002

• Noticed that an M9014 Unibus to H854 adapter was sitting at the bottom of the chassis
• Also received a DELUA, 4 extra double grant (G7273) cards and 3 extra flip chip grant continuity cards
• TU58 console tape drive clogged with mouse fur

Cleaning and Reassembly

30 October 2002

• Tested the blower out of chassis on mains power, worked perfectly
• Brought everything indoors
• Reassembled with original configuration, minus the TU58, which awaits cleaning.

Initial Power-Up

1 November 2002

• "Power" light on 854 power controller lights up when plugged in
• No key for the front panel power switch provided
• Power up with 854 power controller set to "Local" turns blower on, but no lights come on.

Received Key for Power Switch

6 November 2002

• Power up with 854 power controller set to "Remote" and key set to anything but "Off" results in blower turning on, but still nothing from the DC side of the power system. Inspection of power supply units reveals that the large cable that connects the 854 controller, the H7104-C 2.5V PSU, and the H7104-D 5V PSU was installed backwards. Corrected. Power on now yields:

( ) = not lit, (0) = lit

( )	POWER OK
(0)	OVER CURRENT
( )	OVER VOLTAGE
(0)	+5V FAIL
(0)	+2.5 FAIL
(0)	REG FAIL
( )	OVER TEMP

Pulling the Cards Again

7 November 2002

Very interesting. Powering up with cards pulled from backplane results in the following lights on the 854 power controller:

( ) = not lit, (0) = lit

( )	POWER OK
( )	OVER CURRENT
( )	OVER VOLTAGE
( )	+5V FAIL
( )	+2.5 FAIL
(0)	REG FAIL
( )	OVER TEMP

So obviously, something is shorting out. It's been suggested that the backplane or its wire harness may be hosed, but will check its wiring against the installation manual before leaping to any hasty conclusions. Might go ahead and clean up the TU58 tonight.

Cleaning the TU58

9 November 2002

Cleaned the TU58. I really doubt if it works, but as long as the PSU is tripping out anyway, I'm stuck, so the tape drive really doesn't matter.

I'm in the process of checking cabinet wiring against the schematic in the VAX 11/750 Installation Manual. Already found a couple discrepancies. This may just be why the PSU is freaking out so much. More to come...

Pulling Apart the 5V PSU

9 November 2002

I pulled apart the H7104-D tonight, and found that the control board has a blown fuse. This could explain the PSU failures. Will try a new fuse tomorrow.

Trying One More Time

11 January 2003

Wow! The PSU has decided to cooperate all of a sudden. The console now gives me:

%%

00000000 16
>>>

This means that the system passed its microverify test. However, it doesn't seem to be listening to the console. According to Lothian's 11/750 FAQ, this is usually due to a failed 1489 RS-232 line receiver on the L0004 UBI. I've ordered a 1489 and a socket, and desoldered the 1489. The fellow I got the machine from is also sending me an L0004, a UDA50 SDI controller, an RL02 disk unit, and an RL11 controller for the RL02. A fellow in Colorado Springs has a pair of RA70 disk drives as well, but no RA7x enclosure. Apparently, these drives only work with a special control panel. If I can get that enclosure, I should be able to get the 750 up and running. Then, my only remaining wishes for the unit will be an L0001 FPA (not a big priority), a 9-track tape unit (TU8x), a BA-11K expansion cab, and the front and back panels. This unit obviously was coupled to a BA-11K, as there was a DEC power bus cord going from the 875 power controller coiled up in the bottom of the chassis, the left side panel was missing, and the knockouts for that side were knocked out. All that equipment will be a tight fit in my computer room, but I think it should work.

Paying for Hard Drives

18 January 2003

Sent a money order off to Colorado for a pair of RA70 drives.