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Old 24th Jan 2023, 1:42 pm   #1
TonyDuell
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Default Philips P2000C luggable CP/M computer

I was given a Philips P2000C luggable CP/M computer some time back
which had not been well-stored. It took a bit of work to get it going
again.

The basic desgn is a single-board computer with a Z80A, 64K RAM, 4K
ROM (bootstrap and a machine code monitor), floppy disk controller,
SASI interface and 3 serial port. One for an external printer, one for
communications [1] and one to provide a 19200 baud link to the other
main circuit board. This is an intellegent terminal with another Z80A,
32K RAM, video circuitry, keyboard interface and of course a serial
port

[1] Standards are wonderful, everybody should have one of their own...
This serial port is on a DB25 connectorr with the normal RS232 pinout,
but normal RS232 cables probably won't work. The reason is that
Philips decided to support synchronous operation too. So the serial
chp (Z80A-SIO) clocks come from pins 15 and 17 on the connector via
level shifters. The baud rate generator (one channel of a Z80A-CTC) is
level shifted and comes out on pin 24 of the connector. You therefore
need to strap 15-17-24 in the cable plug for normal asynchronous
operation.

Getting back to the machine, as well as the 2 main boards, there's a
switch-mode power supply, a Misubishi 9" green screen CRT monitor (Why
not Philips, they were certainly making such things at the time), a
pair of Teac FD55 floppy drives (of which more later) anf the'power
distribution PCB' to link them all toghether. Oh, and trivial things
like the keyboard cable and mains input wiirng.

I have the Philips service manual which contains schematcs for the 2
main boards but not the rest. I also have the Teac service manual for
the floppy drives.

Obvious faults on first inspection were that the mains on/off switch
didn't latch properly, there was a lot of corrosion, and the carrying
strap was missing. The last is important as to carry the machine you
put the keyboard over the front panel, then slot the strap end
fittings in place which also retain the keyboard.

I took the machine apart and found that the terminal PCB at the back
had suffered badly from poor storage. So had the disk drives, the
spindle bearings felt very rough. The aluminium chassis had surface
corrosion. Screws were very rusty (but standard M3 and M4 parts are
not hard to get). The rest didn't look too bad.

Time to sort some things out. I traced out the schematics for the
power supply, monitor and the power distibution stuff.

There were some RIFA 'smokebomb' capacitors on the PSU board which I
replaced before they did their antisocial act. Since the mains switch
was out of action I coupled a suicide lead to the power supply input
pins with a chocolate block and carefully powered it up with a light
bulb in series. The power supply worked first time.

Tried the monitor board, running it on the bench supply. This powered
up too, the high voltages came up but were low. As I didn'y have the
deflection yoke connected this didn't worry me. So I put the monitor
chassis, PCB and CRT bak togther and connected it and the terminal PCB
to the units power supply.

Powered up, the screen was full of odd characters. It was clear the
terminal processor wasn't doing the right things. Some checks showed
the data lines on the RAMs were not looking right.Well, a couple were,
but not the rest. Cut out the old RAMs, most of the DIL packages fell
apart (!), fitted sockets and new 4116s. Corrected one open-circuit
PCB trace too. Powered up again ,it seemed to work.

Tried connecting the main board. It powered up and even gave the right
startup screen asking for a system disk. Of course no drives or
keyboard at this point, but it was a good sign.

Took the keyboard apart, took off all the keycaps and removed the
dregs of many cups of coffee. Put the keycaps back on.

The keyboard cable, right-angled 6 pin DIN plugs at each end, was a
mess. Insulation crumbling off, green corrosion of the wiring.
Fortunately the plugs are not moulded, so I could open them up, remove
the dead cable and rewire wit ha length of 6 core screened. It's not
coiled stretchy stuff like the original, but it's electrically fine.

Time to sort out the mains switch. I took it apart. An internal, tiny,
spring was so badly corroded that it fell apart when I touched it.
Other bits didn't look great either. My junk box disgorged an
electrically-suitable switch that was actually a spare for a TV set.
Only problems were that the pushrod to fit the button onto was 1/8"
square (the original one for the P2000C was 3mm) and the mounting was
very different. A file cured te first poblem. Fortunately the switch
mouting was a little plate screwed to the PSU mounting, so I removed
that and milled a block of aluminium to mount the replacement switch.
Soldered the mains harness wires to the new swtich.

While the chassis was apart I measured up and made some suitable end
fittings for the carrying strap. Oriiginals were plastic, I made
aluminium ones. Not too hard in that the tongue that goes into the
P2000C catch is 30mm wide by 2mm thick and amazingly a local-ish DIY
shed had 1m lengths of 2mm aluminium strip 30mm wide in stock. Cut
lengths of that, drilled and milled the hole to engage with the catch,
fitted a metal block to retain the keyboard and an eyebolt into that
to put the strap on.

Now to reasemble the chassis. Fitted the mains wirng, keyboard
connector, distribution PCB, PSU and monitor. Plugged in the terminal
PCB and connected the keyboard. Powered up then reset while holding
<esc> down. This runs a simple self-test of the terminal board. It
failed with a memory problem. I found another bad conneciton, this
time a through-board VIA. Soldered a bit of wire through that and the
terminal board then passed the self-test. I temporarily fitted it to
the chassis so as not to have too many bits hanging on wires. Put the
main PCB on top of the chassis, connected the power, reset, and serial
connectors. Powered up, got the 'system disk' prompt. Pressed <esc>
then and was in the machine code monitor. I could display/change
memory, etc. It was essentially working.

OK, now for the drives. These are Teac FD55A, single sided 40 cylnder.
I took them apart one at a time. Not just to the units in the service
manuak, I also took the head-load unit apart (tiny torsion springs),
the top front chasss (even smaller E-clips), the stepper motor (the
front bearing could not be removed without possibly damaging thngs,
but the rear came off easily with a puller so I fitted a new ball race
here) and the spindle motor (again, new ball races fitted).

Got the drives back togther. They ran nicely on the exerciser. Much
more smooth than they were when I took them out. Connected them to the
Microtest alignment unit and did the head alignment. One oddity was
that both spindle motors were slightly slow (about 295 rpm, not 300)
but a tweak of the pot on the motor PCB cured that

Also set up the disk read VCO on the mainboard as described in the
service manual. It was a little off, I am sure it would have worked,
but I re-set it anyway.

Cabled up drive 0. Powered up and put a 40 cyclnder boot disk in. It
booted. DIR worked too. As did running a program off the disk.

Unplugged things and removed the terminal PCB. Put the 2 drives in
place, fitted their mountings and the chassis top rail. Fitted the
main PCB and terminal PCB to the rear chassis plate. cabled everything
up.

Tried the machine again. It booted. I could format a blank disk in the
second drive and copy the CP/M master too it. The copy then booted
fine.

All that remained was to fit the rear plastic panel and top cover.

Stored the boot disk copy and the keyboard cable in the cubbyhole on
the front panel and put the keyboard on. Clipped on the carrying
strap.

It's not quite over...

I am pretty sure my strap end fittings are strong enough. Not so sure
about the strap itself which is one that came with a sports bag. I
may try to get something stronger.

I was given a few floppies with the machne. The only one it will read
is the 40 cylinder boot disk. Philips, you see made 3 versions of the
machine. One had a pair of 40 cylinder single-head drives (160K each).
The second had a pair of 80 cylinder double head drivs (640K each).
The last had a single 80 cylinder double head drive and apprently you
could fit a 10MByte wnchester internally. I know nothing about that
really..

Confusingly, the manuals call the 160K drive 'single density' and the
640K one 'double densiry' for all both use MFM encoding. But I
digress.

My guess is that at least some of the unreadable floppies are 80
cylinder. It would be worth linking up an external drive to see. Time
to hunt in the junk box again.

Then there's the SASI port. One manual mentioned a hard disk unit to
connect there, a 'Xebec board and 1 or 2 10M drives'. My guess is that
the former is an S1410, the latter a pair of Shugart ST412s or
similar. But it seems crazy to me to try to track down said parts --
the Xebec board has serveral custom ASICs on it, hard drives can
headcrash. Or even worst to use a Xebec controller with a drive
emulator -- why convert bytes to a curious serial stream on the Xebec
board and then back to bytes to store in flash memory on the drive
emulator, or vice versa. It would seem logical to simply make a thing
that connects to the SASI port, accepts the commands set of said S1410
controller and stores the data in flash memory directly. Any
suggestions as to how to do that?

Finally, the terminal board has an external video output It's a 5 pin
DIN socket, separate syncs and analpgue video (not composite). There
is a mention of a 12" monitor in one manual, of course with no model
number. Odd, I wouldn't have thought 12" was much of an improvement
over the built-in 9" unit. I would have expected something larger to
show a group of people at once. But making something to connect to
that output is another project.

Last edited by TonyDuell; 24th Jan 2023 at 1:47 pm.
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Old 24th Jan 2023, 1:54 pm   #2
cmjones01
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Default Re: Philips P2000C luggable CP/M computer

Congratulations on getting it going. Perhaps SASI is close enough to SCSI to allow one of the SCSI-to-SD adapters to work? I have a "SCSI2SD" in my Agilent 16702B logic analyzer to replace the (missing) hard drive and it works well. My Mac SE/30 has a SCSI to PCMCIA adapter (of a type and brand I can't remember, but it came from someone on this forum) with a PCMCIA to CF adapter in it, and that works well too.

At least some of the modern SCSI to Flash adapters are open source, so there may well already be someone who's got them working with SASI. I think the original BBC Micro Winchester disk used SASI, too, and there has definitely been some interest in them in the 'retro' community.

Chris
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Old 24th Jan 2023, 2:07 pm   #3
ParcGwyn
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Default Re: Philips P2000C luggable CP/M computer

This brings back memories, my first 'proper' computer around 1987. I think I paid around £200 for it had been upgraded to dual 720k (may have been 640k) 5 1/4" floppies I also think mine had an amber screen, but could be wrong. I seem to remember that a company was offering an upgrade for these with an 8086 processor but may have mis-remembered.

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Old 24th Jan 2023, 4:03 pm   #4
TonyDuell
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Default Re: Philips P2000C luggable CP/M computer

Philips sold an 8088 coprocessor board for the machine. It's described, with circuit diagrams, in the service manual. I think it was only supported on machines with double-sided 80 cylinder drives. And I don't have it.

Mine is certainly a green screen, the CRT has 'P31' as part of the type number too. Of course a different colour screen is just a CRT swap, and amber screen modifications were not uncommon. I csn't find any mention of other colours in the Philips documentation I have, but that doesn't mean much.

I'll look into the possibilty of modifying a SCSI disk emulator. I do have the user manual for what I think is the correct Xebec bridge board and that gives the command set. So getting something to work is probaably not too hard. Of course I have to decide whether to buy a ready-made thing (which might use custom/programmed ICs and not be fully documented) or whether to re-invent the wheel and make something I fully understand.
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Old 25th Jan 2023, 10:29 am   #5
TonyDuell
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Default Re: Philips P2000C luggable CP/M computer

If anyone is interested I've put some pictures of the machine, its PCBs, etc in my flickr account here :

https://www.flickr.com/photos/tony_d...77720304931970
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Old 25th Jan 2023, 11:09 am   #6
Dave Moll
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Default Re: Philips P2000C luggable CP/M computer

Incidentally, Is the line on the screen saying "Beter een drive heel dan twee kapot" the Dutch for "Better one healthy drive than two dead ones" by any chance? I can't seem to get an online translator working anymore.
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Old 25th Jan 2023, 11:34 am   #7
TonyDuell
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Default Re: Philips P2000C luggable CP/M computer

It's something close to that. I did get Google Translate to have a go at it, the result wasn't perfect but it gave the sense.
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Old 25th Jan 2023, 2:48 pm   #8
Dave Moll
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Default Re: Philips P2000C luggable CP/M computer

I tried again on a different computer, resulting in "Better one drive whole than two broken", so pretty much the same except "whole" rather than "healthy". Anyway, apologies for the digression.
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Old 25th Jan 2023, 5:31 pm   #9
TonyDuell
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Default Re: Philips P2000C luggable CP/M computer

A Dutch friend of mine said he'd translate it as : 'better one working drive then two broken ones' which would seem to make sense here.
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Old 26th Jan 2023, 12:57 pm   #10
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Default Re: Philips P2000C luggable CP/M computer

What an excellent restoration, well written up. Iím sure it took an age to do, as I know you are meticulous in your work. Nice machine. My first disk drives for my BBC B were surplus FD55As. Bought from a company in Covent Garden who had been told by a client to upgrade the drives in new machines before delivery. So a lot of low density drives became surplus. I bought lots, which I then passed on to the BT Microcomputer Club members. Long gone now, sadly.
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Old 26th Jan 2023, 4:11 pm   #11
TonyDuell
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Default Re: Philips P2000C luggable CP/M computer

Regarding the disk drives, the machine either came with 2 FD55A's (40 cylinder single head) or 2 FD55F's (80 cylinder double head). AFAIK nothing else was supported, you couldn't use 40 cylinder double head drives (as in PC 360K drives)

A lot of the disks I have for the machine and the disk images on the web are for the latter type of drive. I've found an ex-BBC-micro 80 cylinder double head Mitsubishi drive in the spares pile which I will try connected up as an external drive to the P2000C assuming I can get said drive to work (I can't get the spindle motor to run, at the moment the drive is in lots of bits while I figure it out)
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