Exidy Sorcerer

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jonb
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Exidy Sorcerer

Post by jonb » Wed Oct 11, 2017 11:43 am

Hi friends

With the Superbrains on hold for a while, due to me getting fed up with them (grrr!), it's time for another "save the old computer from the dump" thread.

This time we have an Exidy Sorcerer, which fell into my lap totally unexpectedly from its previous owner who'd had it from new. It's equipped with a Liveport FDM 180 hard sectored disk drive and should boot into CP/M. Also, a BASIC cartridge that plugs into a slot on the right hand side of the machine, which is encased in a modified ("hacked up" would be nearer the mark) 8-track cartridge case. It boots to the monitor, but no further - and on boot the monitor checks the RAM and gives a value for RAMTOP, a system variable that indicates where the user RAM ends. It is affected by the amaount of memory installed and whether or not a ROM pack is plugged in. The memory map has RAM from 0000-RAMTOP, then above that are plug in ROMs, the monitor, video RAM, character set ROM, graphics characters. I think the upper RAM is not DRAM. When there's no DRAM, the monitor uses the screen ram for its stack.

So. This machine was upgraded in a homebrew sense so that it's got a full 64K of memory. The upgrade entailed piggybacking RAM chips and a few logic chips, plus lots and lots of patch wires. I do have the instructions for this mod, though, so I should be able to work out the schematic.

I started discussing it on VCF: http://www.vcfed.org/forum/showthread.p ... y-Sorcerer

Please save me the effort of retyping all that stuff by reviewing the thread. It is mostly about the disk unit, though; but we'll return to it in a moment.

The first thing I found out was that there was no DRAM operable, with RAMTOP reported as FFFF (apparently a dead givaway!), but this turned out to be a shorted tantalum capacitor pulling the 12v line low. Poxy things! I pulled it and the monitor started reporting a proper RAMTOP value (DFFF), but it would not boot, either to BASIC or the floppy drive.

A documented failure of the BASIC cartridge is bit rot in the ROMs, so I put it to one side and started looking at the floppy drive. The Sorcerer has an S-100 bus for its expansion port, so the floppy drive has a combined S100 interface and drive controller onboard, all done in discrete logic. To boot to CP/M you power them up, insert a boot disk and enter GO BC00 at the monitor prompt.

Interesting, it is like the disk unit has built in ROM that is overlaid on the RAM like the BASIC cartridge. I couldn't see any ROMs on the drive's interface, apart from two 16 pin ICs with labels on them: "3E" and "4E". I pulled one of the labels and discovered they are Signetics N82S126N PROMs:

http://pdf1.alldatasheet.com/datasheet- ... S126N.html

These are 256x4 ROMs which give 256 bytes for the Sorcerer's disk boot code.

As mentioned on the VCF thread, I also spotted a DIP switch that appeared to set the location of the ROM in the Sorcerer's address space. This makes sense as you might need to move it around if you had specific amounts of memory available (I mean, non standard amounts).

As supplied, I think the ROM resides at DE00 (the DIP switch spells out the value DE in binary) but when I looked I only saw a partial set of data. I tried to adjust the DIP switch and moved the ROM to a lower address - 5C00 - and looking at that it appeared that the drive's boot ROM is intact. The quick ones amongst you will spot the discrepancy between the start of the boot ROM at DE00 and the monitor's boot vector (BC00). I think this is due to the instructions being written for a 48k Sorcerer.

I have dismantled the cartridge slot and fitted the ICE. It reports a memory map like this:

Code: Select all

OK ===> md

0000000000000000111111111111111122222222222222223333333333333333
0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF
RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWOOOOWWOW
0000000000000000111111111111111122222222222222223333333333333333
0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF
I tested all the RAM (DRAM and screen RAM) and it came back OK. That's a surprise - I was certain there was some memory breakage. After all, we are dealing with 4116 DRAM here, those chips are notorious for failure but seemingly not in this machine. Also a big relief as the RAM chips are sat on top of each other so any repair would be a swine of a job!

With the drive unit installed the map is different, as we might expect:

Code: Select all

OK ===> md

0000000000000000111111111111111122222222222222223333333333333333
0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF
RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWOOOOOWWOW
0000000000000000111111111111111122222222222222223333333333333333
0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF
There is an extra chunk of ROM in there, which is the boot ROM.

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jonb
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Re: Exidy Sorcerer

Post by jonb » Wed Oct 11, 2017 11:58 am

When we look at this ROM we get some not particularly sensible assembly.

Code: Select all

OK ===> l dc00
DC00 F2 2F A2       JP P,A22F
DC03 00             NOP
DC04 F9             LD SP,HL
DC05 3F             CCF
DC06 C9             RET
DC07 CD A2 0F       CALL 0FA2
DC0A EB             EX DE,HL
DC0B 2A A0 0F       LD HL,(0FA0)
DC0E 2E 00          LD L,00
DC10 E5             PUSH HL
DC11 0F             RRCA
DC12 1D             DEC E
DC13 00             NOP
DC14 01 EF E1       LD BC,E1EF
DC17 0E 12          LD C,12
DC19 0F             RRCA
DC1A 06 BD          LD B,BD
DC1C EB             EX DE,HL
DC1D 3F             CCF
DC1E 3B             DEC SP
DC1F 1A             LD A,(DE)
DC20 70             LD (HL),B
DC21 BF             CP A
DC22 C0             RET NZ
DC23 23             INC HL
DC24 10 0F          DJNZ DC35
DC26 C0             RET NZ
DC27 E1             POP HL
DC28 20 AF          JR NZ,DBD9
DC2A 00             NOP
DC2B 11 00 0F       LD DE,0F00
DC2E 19             ADD HL,DE
DC2F 22 A2 0F       LD (0FA2),HL
DC32 36 A0          LD (HL),A0
DC34 C0             RET NZ
DC35 DF             RST 18
DC36 00             NOP
DC37 00             NOP
Maybe the ROMs are corrupt... in which case, "game over"!

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Re: Exidy Sorcerer

Post by tricky » Wed Oct 11, 2017 7:34 pm

I had always fancied an Exidy sorcerer, assuming that it was 6502 based like the Exidy arcade games Circus/Acrobat TV and RipCord that I wrote emulators for for the beeb (see my sig). Now I see it is z80 (maybe - I'm 35 years rusty), I'm not interested in owning one, but I would like to see brought back to like.
Good luck.

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Re: Exidy Sorcerer

Post by DutchAcorn » Wed Oct 11, 2017 8:12 pm

Have you tried loading from tape? I have a nice game for download here (Interceptor, 1200 baud wav).
Paul

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Re: Exidy Sorcerer

Post by jonb » Wed Oct 11, 2017 9:53 pm

Good idea! Will try tomorrow.

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Re: Exidy Sorcerer

Post by jonb » Thu Oct 12, 2017 10:55 am

Meanwhile, per http://www.classic-computers.org.nz/blo ... part-1.htm

I had a look at the BASIC ROMs and discovered that ROM#3 has failed. No wonder it won't boot to BASIC.. Now I need to acquire a 2716 EPROM - anyone got a spare?

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Re: Exidy Sorcerer

Post by jonb » Thu Oct 12, 2017 11:20 am

Alright... turned out I have a spare 2816 EEPROM left over from the Superbrain project, which is pin compatible with the 2716 EPROM.

I programmed up the BASIC-3 ROM from a dump I'd got off the Internet and fitted it. Seems to work..
IMG_1006.JPG
Exidy BASIC (C)1978!
...but the screen display gets corrupted after running the program. You can't see it in the picture, but the E of READY (after the program output) is sort of flickering, and "hist" should be "list". Some characters in the listing are flickering too, and the [ prompt is wrong. Interesingly, since taking the picture the listing has cleaned up a bit, so I suspect the shift register, character ROM or screen memory may be at fault. Need to test some more!

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Re: Exidy Sorcerer

Post by jonb » Thu Oct 12, 2017 11:45 am

DutchAcorn wrote:Have you tried loading from tape? I have a nice game for download here (Interceptor, 1200 baud wav).
I'm seeing tape CRC errors. Also tried a MP3 of CHOMP - same problem. Possibly audio volume related but I've turned it up as far as possible. I'm feeding the Sorcerer from the headphone jack on my iMac, might need an amp...

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Re: Exidy Sorcerer

Post by jonb » Thu Oct 12, 2017 3:33 pm

Regarding the screen corruption. A chap I am corresponding with who used to import Sorcerers says they are susceptible to electrical interference.

There are some big caps on the board, in particular a very large electrolytic - 8000uf @15v - this is the main smoothing cap for the 5v supply. It feeds the 5v voltage regulator. The 'scope traces look OK-ish.. what do you think? I'm never sure what is acceptable noise levels on a microcomputer board.
DS1Z_QuickPrint37.png
Rails: Y=5v, C=19v, M=-12v. C & M are at the caps, before the regulators.
Maybe I should look to replace the caps, especially the smaller two.

Also there is a chunky EMI filter on the mains side of the transformer - isn't this to protect the mains from computer induced interference?

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Re: Exidy Sorcerer

Post by jonb » Thu Oct 12, 2017 3:51 pm

A quick test with some new caps I had lying about gave slightly better results, especially for the 19v line.

BASIC appears to be steadier but there is still some screen corruption (especially in the m/c monitor, after looking at memory contents).

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Re: Exidy Sorcerer

Post by DutchAcorn » Thu Oct 12, 2017 6:04 pm

jonb wrote:
DutchAcorn wrote:Have you tried loading from tape? I have a nice game for download here (Interceptor, 1200 baud wav).
I'm seeing tape CRC errors. Also tried a MP3 of CHOMP - same problem. Possibly audio volume related but I've turned it up as far as possible. I'm feeding the Sorcerer from the headphone jack on my iMac, might need an amp...
Try the 300 baud versions? Interceptor, Chomp (large files). As you probably know you need to set the baud rate to 300 baud in the monitor first with the SE T=1 command.
Paul

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Re: Exidy Sorcerer

Post by jonb » Fri Oct 13, 2017 7:07 am

OK Paul, will give that a try later.

Meanwhile I ordered a bunch of new caps for the poor old thing plus a shift register, because I think that is causing the screen flicker. There's a buffer / line driver IC in the circuit, too, but I think that the shift register is more likely to be at fault.

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Re: Exidy Sorcerer

Post by hoglet » Fri Oct 13, 2017 8:40 am

Jon,

Was the original ROM a 2716 EPROM? Have you tried just erasing it and reprogramming it?

Dave

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Re: Exidy Sorcerer

Post by jonb » Fri Oct 13, 2017 10:09 am

hoglet wrote:Jon,

Was the original ROM a 2716 EPROM? Have you tried just erasing it and reprogramming it?

Dave
Mask ROM by the looks of it - no U/V eraser window, despite being listed in the parts table as 2716 PROM. The monitor ROMs are proper EPROMS, though; really pretty white ceramic ones with gold plated legs. I'm guessing they were added later by the original owner.

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Re: Exidy Sorcerer

Post by crj » Fri Oct 13, 2017 1:01 pm

I assume you've checked the part number and it's not an EEPROM?

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Re: Exidy Sorcerer

Post by jonb » Fri Oct 13, 2017 2:48 pm

crj wrote:I assume you've checked the part number and it's not an EEPROM?
Good point but I can't find a datasheet for it.

7842E C28418M, possibly ST microelectronics. This computer is nearly 40 years old - did they even have EEPROM back then?

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Re: Exidy Sorcerer

Post by jonb » Fri Oct 13, 2017 3:21 pm

Incidentally... the floppy drive has a boot ROM built into it. Signetics N82S126N PROM x 2, which (as I mentioned) appear to be partially corrupted. Does anyone know how I can verify the contents without using the Sorcerer or drive unit?

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Re: Exidy Sorcerer

Post by crj » Fri Oct 13, 2017 3:24 pm

I was thinking that, if you have several ceramic EPROMS and one plastic package, the plastic-packaged memory might not be original. In which case it could rather newer.

I'm not finding that part number either, though. )-8

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Re: Exidy Sorcerer

Post by jonb » Fri Oct 13, 2017 3:28 pm

jonb wrote:
crj wrote:I assume you've checked the part number and it's not an EEPROM?
Good point but I can't find a datasheet for it.

7842E C28418M, possibly ST microelectronics. This computer is nearly 40 years old - did they even have EEPROM back then?
Picccie time!
IMG_1008.JPG

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Re: Exidy Sorcerer

Post by jonb » Fri Oct 13, 2017 3:35 pm

crj wrote:I was thinking that, if you have several ceramic EPROMS and one plastic package, the plastic-packaged memory might not be original. In which case it could rather newer.

I'm not finding that part number either, though. )-8
Look at the picture I posted - I am not sure who the maker is. Regarding the layout, the ceramic ROMs are on the motherboard, but the BASIC ROMS are in a slot-in cartridge made from a hacked up 8-track case. Not homebrew either, that is how it came from the factory! There's a slot in the right hand side of the computer angled at ~30 degrees from horizontal into which you shove the cartridge if you fancy a nice bit o' 1978 vintage BASIC. Looks odd, because the end of the cartridge likewise sticks up at 30 degrees. See :

http://jscustom.theoldcomputer.com/imag ... system.jpg

Anyway... it's a proper weirdo machine, that's for sure..

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Re: Exidy Sorcerer

Post by crj » Fri Oct 13, 2017 5:41 pm

My Google-fu seems to be strong: the manufacturer is Synertek (1973-1985).

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Re: Exidy Sorcerer

Post by DutchAcorn » Fri Oct 13, 2017 7:40 pm

jonb wrote:
hoglet wrote:Jon,

Was the original ROM a 2716 EPROM? Have you tried just erasing it and reprogramming it?

Dave
Mask ROM by the looks of it - no U/V eraser window, despite being listed in the parts table as 2716 PROM. The monitor ROMs are proper EPROMS, though; really pretty white ceramic ones with gold plated legs. I'm guessing they were added later by the original owner.
There were different versions of the Monitor, possibly 1.1 was installed?
Paul

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Re: Exidy Sorcerer

Post by jonb » Sat Oct 14, 2017 7:05 am

True, and I do have 1.1 according to the labels on the ICs.

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Re: Exidy Sorcerer

Post by jonb » Sun Oct 15, 2017 9:04 pm

Ok, I think I've tracked the video noise down to the 2114 video RAM. The flickering vanishes when you heat the chips up with a hairdryer! And stays gone. Applying freeze spray doesn't make it return, which is odd. Might try some nearby chips too, just to be sure.

Meanwhile, I made progress with the S-100 drive. Looks like the ROMs might be OK, but there's something bad going on with the interface logic. I need to reverse engineer the board.. oh happy day..

The drive motor keeps coming on briefly. Like a loose connection, its twitchy. Could be noise in the PSU, it's another one of those old linear jobs. Scope out...

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Re: Exidy Sorcerer

Post by jonb » Wed Oct 18, 2017 10:51 am

Whilst waiting for some 18 pin DIL sockets to arrive, I thought I'd renew some of the tantalum capacitors; in particular the two that had gone closed circuit. Previous tests, obviously, were carried out without these in place. I also replaced the tants around the DRAM chips (these are not used for screen memory). Anyway, on restart it seems all the video artefacts are gone and I'm at a bit of a loss to explain why. There was a small amount of noise on the 5v rail but not enough to affect TTL levels. Maybe there is a dry joint, but I already reflowed all the video RAM, which didn't help. Oh, well...
IMG_1011.JPG
Sorcerer rides again!
So, what has been done so far?
  • Replace two large smoothing caps in the linear PSU
  • Replace all .33uf 25v tatalum caps (two of which were short circuited)
  • Replace ROM 3 in the BASIC cartridge
  • Straighten and refit the 12v voltage regulator's heatsink
  • Clean the 50 way expansion port edge connector

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Re: Exidy Sorcerer

Post by jonb » Wed Oct 18, 2017 11:05 am

To make further progress with this machine we must start to look at the disk drive. It's a British designed and made unit, featuring a custom interface to connect to the Sorcerer's expansion port via a 50 way edge connector and uses hard sectored 5 1/4 floppies (AKA rocking horse poo). I have 10 disks, two of which purport to have CP/M on them; and all suffer from fungus / mould attack. It's not too mad on the magnetic surface of the disks, but the linings on the inside of the disk envelopes are pretty brown.
IMG_1012.JPG
Yuk!
Nasty - but not the end of the world. It's possible to take the disk itself out, wash in soap and water and fit into a clean sleeve from another disk, as Tezza explains here http://www.classic-computers.org.nz/blo ... -water.htm

I may or may not be able to pull data from the precious CP/M disks...

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Re: Exidy Sorcerer

Post by jonb » Wed Oct 18, 2017 11:17 am

Looks like I spoke too soon!

Screen corruption occurred again in the m/c monitor when dumping out memory.
image.jpg
Sigh..
Those dollar signs weren't there before, and it is happening in BASIC too. Not to worry though, I have the sockets on order and I found some spare 2114s from the Atom (after upgrading it to use Prime's RAM/ROM solution).

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Re: Exidy Sorcerer

Post by jonb » Mon Oct 23, 2017 8:10 am

Time on my hands... so I swapped out three of the six 2114 DRAMs and I think it is OK, fingers crossed.

Now loading Chomp at 300 baud. No errors so far and I'm about half way through it. The WAV file is 7 minutes long! I'm thinking I can use this as a sort of soak test to see if all's well .

[edit: Loaded and run, but seems to have crashed right after the opening animation. Darn it. Maybe I should swap out the other three 2114s.]

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Re: Exidy Sorcerer

Post by jonb » Mon Oct 23, 2017 9:11 am

Interesting.. I stumbled upon an online emulation of the Sorcerer here: http://www.liaquay.co.uk/

It wouldn't run in my browser but it will work standalone. There's a ZIP file download. Anyway, it contains disk images for CP/M 1.4 and ROM images (z80 dev pack, word processor, various BASICs) plus games. Handy - and the CP/M disk appears to have a full listing of the Exidy CBIOS! 8)

This will be very handy indeed, should I succeed in getting the floppy drive to work. And it has the disk boot ROM too!

Code: Select all

00000000  f3 21 a2 00 f9 36 c9 cd  a2 00 eb 2a a0 00 2e 00  |.!...6.....*....|
00000010  e5 01 1d 00 09 e5 e1 0e  1a 09 06 bd eb 3b 3b 1a  |.............;;.|
00000020  77 be c0 23 13 05 c0 e1  2a a0 00 11 00 02 19 22  |w..#....*......"|
00000030  a2 00 36 a0 c3 d4 00 00  00 00 00 2a a2 00 7e e6  |..6........*..~.|
00000040  80 ca a9 00 7e e6 0f a8  c2 a9 00 23 b6 f2 b7 00  |....~......#....|
00000050  23 7e af eb 06 00 00 00  1a 77 23 88 47 1a 77 23  |#~.......w#.G.w#|
00000060  88 47 0d c2 c3 00 1a b8  c9 2a a2 00 36 20 23 7e  |.G.......*..6 #~|
00000070  2b e6 24 ee 20 c2 d4 00  0e 5e cd 49 01 23 7e 2b  |+.$. ....^.I.#~+|
00000080  e6 24 ee 20 c2 d4 00 23  7e e6 08 2b ca 07 01 06  |.$. ...#~..+....|
00000090  08 36 61 0e 0f cd 49 01  05 c2 fc 00 23 7e e6 08  |.6a...I.....#~..|
000000a0  2b c2 19 01 36 60 0e 0f  cd 49 01 c3 07 01 21 5f  |+...6`...I....!_|
000000b0  01 cd 37 01 c2 d4 00 2a  69 02 22 a4 00 cd 37 01  |..7....*i."...7.|
000000c0  c2 d4 00 2a a4 00 11 0c  00 19 d1 e9 e5 eb 01 86  |...*............|
000000d0  00 cd a6 00 e1 c2 37 01  e5 7e 23 b6 e1 c9 7e e6  |......7..~#...~.|
000000e0  20 79 c2 51 01 07 4f 3e  ff d6 01 b7 c2 54 01 0d  | y.Q..O>.....T..|
000000f0  c2 52 01 c9 00 00 00 00  00 00 00 00 00 c3 a6 00  |.R..............|

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Re: Exidy Sorcerer

Post by jonb » Mon Oct 23, 2017 9:57 am

Running a simple BASIC program for an hour shows no unwanted screen artefacts so I think we're good.

Code: Select all

10 PRINT A
20 A+A=.0001
30 GOTO 10

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