Sharp x68000 Repair

[Arcade King]

I'll be working on this thread over the next several days so it will stay closed until completed.

As a Retro Arcade, Computer and Console enthusiast I think it's all our dreams to own somthing special like the Sharp x68000 which was the pinacle of 16 bit computers of the day even stomping on greats like the Amiga.

I recently purchased 2 orignal model (OG) Sharp x68000's (CZ-600CE) , one from Ebay the other from a Japanese Proxy site. The one from Ebay I found out was some guy pre listing the computer on Ebay. This is why you some times see the same item from Japan listed from multiple sellers on Ebay. You buy it from them, they then buy it from what ever Japanese site it was listed on, have it sent to them, then they send it to you.

As I found out with the second computer it's far cheaper to use a Japanese Proxy site and buy it directly from the seller.

A Run down on both machines.

Both machines came without keyboard and mouse which is pretty common and both listed as Junk.

Ebay machine.

This machine had obviously been worked on before. I'd say it's a very early model, there are a lot of jumpers and external parts added to all of the PCB's. The case has been damaged with tabs that clip the case together broken off , many screws missing, RF shielding missing, internal speaker was missing and lastly the floppy status indicator LED board missing 😕 other than that all boards and floppy drives present.

Proxy site machine.

Later revision, all boards very clean without the hacks found on the earlier revision, Everything present in this machine including screws, RF shielding, Floppy drives, Speaker etc.

Both machines didn't have the 1mb upgrade. 😞 I havent seen any come up for sale as of yet and you need at least 2mb to run most games.

From here on I'll just call them x68k 1 (Ebay) and X68k 2 (Proxy)

Before even attempting to power on the machines it's important to either rebuild the original PSU and run off a 100vac step down or in my case I used a more modern solution called X68k Pico PSU v2 created by mattsoft and is open source on github. https://github.com/mattsoft/X68K_Pico_PSU_v2

Its essentially a board that replaces the guts of an original x68000 psu with a ATX PicoPSU https://mini-box.com.au/product/picopsu-120-120w/

Original PSU

X68k PicoPSU

I would have prefered somthing that fit direcly into the existing case however I adapted it for now and works fine.

This board was designed for later model machines like the ACE, Expert, PRO etc with the "Tetris" style PSU. The PSU was changed from the OG rectangular style to the Tetris style to make room for a SCSI hard drive.

Because I need a second PSU for my other machine I decided to redesign the board using KiCad to better suit OG models.

Firstly I measured the original PSU case which has spacers already installed to screw down the PSU's internal so I've made the board larger to suit. Secondly I've done away with the screw terminals in favour of 3.96mm Molex headers and plugs which I use all the time in my Pinball repairs. I've moved the headers closer to the top right to get everything closer to the hole for the wires. The last change was adding extra terminals for the +5VSB which is Standby power which like on modern PC's is used to soft start the computer with the button on the front, it's also used for ejecting disks when the machine is in standby mode with a button on the back on the X68k.

There are 3 white wires on the OG x68k for +5vSB with only 1 terminal on the Tetris PicoPSU board which makes it hard. On mine I've made sure there is enough room for all wires.

Crossing my fingers when my boards come back they will fit in.

UPDATE.

I wasn't happy with my v1 board so I had it remade doubling the track size from 1.5 to 3.0mm and added a Molex header in for the 12v fan, something I should have done in the first place.

V1 vs V2

Everything neatly installed.

and back in the machine. You wouldnt even know it wasnt the original psu.

I can confirm everything is powering up and working beautifully 🙂

[Arcade King]

Now We have the PSU sorted its time to look at the boards.

x68000 boards are split into 3.

Info can be found of the Wiki https://en.wikipedia.org/wiki/X68000

The main CPU or "Core" board which as the main 68000 CPU clocked at 10mhz, 1mb of roms , 16k of Battery backed up SRAM (bottom right) and the CYNTHIA sprite controller chip at the top left.

Video Board which has the VSPO video processor and VRAM

and lastly Peripheral board which sits at the bottom and tends to get very dirty with dust and crap. This board has the sound, floppy and SASI controller hardware.

x68k 1 Repair.

First off was to give the dirty Peripheral board a clean and deal with the battery on the main CPU (Core) board.

It's well documented that the biggest killers of the OG x68000's is battery leakage from the old 3.6v Ni-CD battery which sits right next to the main 69mhz crystal and reset chip.

As you can see somebody had already clipped out the battery and luckily minimum damage done. This early CE has the crystal on a some standoff which is super lucky, most have them flat on the board.

I decided to use a 3.6 volt lithium battery with axial leads. Looking at the schematics it's just a matter of cutting off the charge resistor R88 and install the battery.

Eventually I'll replace it with a coin battery but this will do for now.

At this point I reassembled the machine and powered it on. and from what I could tell it was booting. The Power led turns from red to green and Hi RESQ led comes on. Turning the machine off with the soft on/off buttom the green led flashes several times them goes red. A VERY good sign! unfortunately my SCART cable hadn't arrived so I couldnt verify if anything was on the screen.

Cable finally arrived. I'm running the Scart cable though my OSSC scan converter to a DELL 2007FPB

and she is in fact alive! Message reads "Unable to book from disk. Set the correct Disk"

This is as far as I got with this machine. Inserting a disk it would spin for a bit then eject it back out on both drives, I tried cleaning the heads, recapped both drives etc with no luck. The heads would just sit there and didnt look like it was even trying to seek. Without a working drive I was reluctant to take it any further. 

Thinking what are the chances both drives could be bad I thought the fault may be on the Peripheral board however no luck there even after changing the NEC flopper controller chip and SED9420AC CMOS data separator IC still nothing. At this point I made the decision to buy another junk machine for parts.

Writing Floppys.

I used 2 different Retro PC in m y collection, a 1500mhz P3 and a 386 DX40 with 5 1/4" disk drives to write x68000 disks using Omniflop on Win XP and Xfloppy on Win 98 and 95. I had doubts because I didnt have any original disks to verify if it was the issue the drive wasnt reading however I can confirm both programs work fine.

No point going over this as it's already well documented.

https://gamesx.com/wiki/doku.php?id=x68000:writing_floppies

 

A lot of images are in the DIM format and will need to be converted to a raw format XDF. I recommend vf011010

https://nfggames.com/X68000/index.php/PC_Tools/Disk/?upload=1

Disk Drive Status LED board

For what ever reason the LED indicator board was removed form this machine. 0 drive is supposed to flash green when no disk inserted then solid green when inserted and changed red when read/writing.

I basically just made my own from some veroboard, 2 x 3 pin Red/Green LED's (3 colour) and Micro JST 2.0mm 3 pin connectors.

I'll leave it here for now 🙂

[Arcade King]

Updated first post 30/05/2023

Added pics of Pico PSU board v2.0 fitted and up and running at the end of the first post 🙂