Pulsar 7500 Initial Power Up and Fault Finding

I connected it up to a serial terminal, but I couldn’t get anything out of any external serial port.  The hard disk did not spin, so it may be a lost cause.

I had no boot disks for the floppy disk, although i thought it may be possible to create some from the 8″ disk collection. Many of the disks were related to Pulsar – both CP/M and TurboDOS.

Working in the case was a little cumbersome, so I pulled the system right down to the boards:

It consists of:

  • 1x Master LBB with STD and Floppy Drive Interfaces
  • 4x Slave LBB (with a variety of options which are probably not used)
  • 2x SASI/Dual Serial Boards
  • 1x Mitsubishi M4854-342 High Density Floppy Disk Drive
  • 1x NEC LR 56913Hard disk drive with Adaptec ACB-4000 SASI adapter
  • 1x Sysquest removable disk drive with Adaptec ACB-4000 SCSI adapter (external to computer and mounted on it’s own baseplate)

There is a lot of variation amongst the slaves. Perhaps from card swaps over the years, or perhaps this machine was put together using whatever was in stock. Serial port connectors can be straight or right-angled, a bare header, or a shrouded header, sometimes with release levers.

Each of the slaves is connected via serial to the SASI/Serial cards. The master owns the bus and therefore the SASI/Serial cards. The slaves must not attempt to use the STD bus, so where the interface is loaded it has to be nobbled with track cuts.

There seems to be no reason why the slaves need to be in the unit – they could just as easily be located elsewhere but there is not a lot to be gained as either way a serial connection is required.

The serial ports on the master were used for printers.

I tested each of the boards with an MP7A Monitor ROM in a different chassis.

The master little big board does come up ok, so probably it was silent at switch on because that’s how the boot ROM rolls.

Two of the slaves were ok, but the other two were not working. One had a bad solder joint and the other had lost 12V connectivity because the track is very close to the board edge was severed.  The damage would have occurred when I levered the board out of the backplane (there was no other way).

I could not get the master to boot from the floppy disk, even after adjusting the phase-locked loop as per Pulsar instructions. I parked that board and used a spare, which did boot.

From there the configuration tool was used to setup the slaves.  There are a lot of questions about each slave.  I took the easy options with automatic login of the privileged user.

Pulsar 7500 Floppy Disk Drive

The 7500 system uses a 5.25” drive rather than an 8″. As it turns out, the floppy disk drive in this unit, Mitsubishi 4854-342, is intended as an 8″ replacement – it even claims to be a 77 track drive although i suspect it’s good for 80. 

https://retrocmp.de/fdd/mitsubi/m4854_i.htm

The 50 pin host interface is connected to the 34 pin drive interface via a simple adapter. All up, this means that the 8” images can be written to HD 5.25” disks.

Looking at the simple 50/34 adapter board, I suspect that the drive has a couple of signals that may not be present on a 5.25” interface – Ready and 2Sides. I imagine that 2Sides is always asserted because there is no way for a 5.25″ drive to know if a disk is single sided. 8″ drives can.

The drive was cleaned and lubricated and tested ok with Imagedisk.

8” Pin8” SIgnal5.25” Pin5.25” AdapterComments for Emulation with Gotek
2TG43_LNot used
4
6
8
102SIDES_L2REDWC_LNot driven by controller or gotek.  Pull down
12
14SIDESEL32SIDESEL
16
18HEADLOAD_L4Not Used
20INDEX_L8INDEX_L
22READY_L34DISKCHG_L
24
26DS010DS0
28DS112DS1
30DS214DS2
32DS36DS3
34DIRC_L18DIRC_L
36STEP_L20STEP_L
38WDATA_L22WDATA_L
40WGATE_L24WGATE_L
42TRACK0_L26TRACK0_L
44WRTPRT_L28WRTPRT_L
46RDATA_L30RDATA_L
48
50
16MOTORON

I wrote an HD floppy disk from 8″ disk image 8_257_02 (Pulsar Turbo V1.3 Master Configuration Sys 14 Config V24 Single User) using greaseweazle.