.:[Sun 3/50 System with Upgrades]:.

Topic: The worst Sun3 system, improved somewhat
Date:  2022 SEP 19

In spring 2019, Guy Fedorkow was looking to find a new home for a Sun 3/50 he had. He’d mentioned it on the ClassicCmp mailing list, and I responded. We were able to meet up at the MIT Flea, avoiding the hassle and expense of shipping.

The Sun 3/50 was Sun’s lowest-end Sun-3 offering: it had the slowest clocked processor, the FPU was optional, and RAM was hardware limited to 4 MB. Many revisions of the boot ROM and monitor could boot only from a limited set of devices, often restricted to specific models of tape drives and/or specific SCSI IDs. This low-end system was intended to be a (relatively) cheap diskless workstation, for environments like computer labs. Apparently, some were also used as netbooted X terminals. Specs as follows:

  • Motorola 68020 processor at 15 MHz
  • Optional Motorola 68881 FPU (present in mine)
  • Sun-3 MMU with 8 hardware contexts
  • 4 MB physical memory (hardware limited to 4 MB)/256 MB virtual memory
  • Cycle-stealing ECL monochrome framebuffer
  • Onboard SCSI
  • Onboard Ethernet, AUI/BNC switchable

The Sun 3/50 is packaged in a pizzabox form factor. The chassis is a single 9U Sun VME “sleeve,” essentially, providing only power. Some of the Sun 3/50 enclosures have a dimple in the top, intended to directly mount an ECL monitor. Mine does not, but it does have the “shadow” of a large monitor that must’ve set on top of it.

Guy had the Sun 3/50, a Sun type 3 keyboard and mouse, and an Ethernet transceiver, but no display. He’d put me in contact with a friend with a possible Sun ECL monitor. We met up at VCF Midwest and I picked up the display, but it turned out to be the Sun non-ECL monochrome display. While that wouldn’t work with the Sun 3/50, it does work with my Sun SPARCstation 2. Without a display, the Sun 3/50 would be running with a serial terminal console:

Sun 3/50 booting

Above is the Sun 3/50 on the workbench, with a DEC VT320 as the console terminal, and a heap of external SCSI mess next to it. There’s a big mess because I didn’t fully understand the limitations of the installed boot ROM when I started bringing this system up!

Before powering the system up, I disassembled and cleaned it. I was very surprised when I pulled the system board and found this:

Sun 3/50 system board with Parity Systems upgrade Parity Systems upgrade board installed

It’s an upgrade board! There are several third-party upgrade options for the Sun 3/50, including boards from Clearpoint, Solflower, and Helios. My upgrade is made by Parity Systems, and I have been unable to find any information on it. It’s actually two boards:

Parity Systems Sun 3/50 upgrade main board Parity Systems Sun 3/50 upgrade MMU board

The big board in the picture to the left is the main portion of the upgrade. It connects to the board in the picture on the right via a small ribbon cable, seen in the left picture. The board on the right is a MMU upgrade. Having these two boards separate probably made fitting them to the Sun 3/50 system board easier. They attach with a number of DIP feedthroughs to PAL/GAL sockets, and these two PLCC adapters:

PLCC adapters on Sun 3/50 upgrade

Aside from the dead clock/NVRAM battery, this Sun 3/50 did require one other repair:

Corroded tantalum capacitor New tantalum capacitor

An axial tantalum capacitor near the DC-DC converter block in the Ethernet section had released its electrolyte and corroded one lead completely open. It was replaced with a NOS 220 uF 10V hermetically sealed axial tantalum capacitor.

The Sun 3/50 system board was given a thorough cleaning, the Parity Systems upgrade was reinstalled, and the board was ready to go:

Parity Systems upgrade reinstalled

The system came up with no problems, other than a corrupted NVRAM. Setting the diag-switch and re-configuring the NVRAM resolved this. The console was set to serial port A, at 9600 BPS. A netboot was attempted, to ensure that Ethernet was working properly.

I’d purchased a Sun external drive box to go with the Sun 3/50, I believe it’s a Sun EXT-1. It includes space for a full height 5.25” hard disk and tape drive. It came with both installed, but the hard drive was completely dead. The QIC tape drive installed in the box required cleaning, as it was packed full of filth:

Dirty QIC tape drive Tape drive fluff

After cleaning and lubrication, the QIC drive worked fine. A 2.1 GB SCA drive was installed in place of the original 5.25” full height drive, with an adapter. The box was cabled to the Sun 3/50 using a DD50 cable, which until very recently were available brand-new from Monoprice (since discontinued). Install tapes for SunOS 4.1.1 were made with another Sun system. The tape cartridges required new belts, of course. The Sun 3/50 booted the new tapes just fine, albeit very slowly. Installation proceeded normally until the reboot into the miniroot install environment.

After installing the miniroot, the Sun 3/50 refused to boot it! I’d get cryptic error messages that I hadn’t encountered before. It didn’t help that this was the first Sun-3 machine I’d started from scratch with. After trying other SCSI drives, including a SCSI2SD with 2 GB industrial SD card, I decided I must be doing something wrong and started digging. The answer was found in the SunOS Install Media page on the Sun3 Archive. With older PROM versions, the Sun 3/50 can only boot from sd0! I’d been using the “standard” first drive ID from Sun-4 land, SCSI ID 3, which is sd6 in Sun-3 land.

A re-addressing of the SCSI drive and reinstall of the miniroot to sd0 got the Sun 3/50 install going. Installing from QIC tape is…not fast. It did eventually complete without error, though:

SunOS 4.1.1 booting on Sun 3/50 SunOS 4.1.1 boot message closeup

Note that the kernel shows 8 MB RAM installed! The Parity Systems upgrade does have empty RAM SIMM sockets, but populating them did not increase available memory. I’m not sure if this is some jumper change I was missing, or if a PAL/GAL upgrade is also required. If anyone has information on the Parity Systems upgrade board, please contact us!

third party upgrades installed

Copyright (c) 2023 Jonathan Chapman