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Category: Retro Computers

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Old Hardware Retro Computers

X68030 SCSI Adventure Part 1

I finally got SCSI working on my X68030 CZ-500C, so thought I’d do a writeup on what I learned. It will be in two parts, where the first one covers the default CZ-500C SCSI support, and the second part covers a new adapter I made for using internal SCSI devices.

CZ-500C SCSI Internals

X68030 has proper SCSI support, not just SASI as some of the earlier X68000 models. CZ-500C does however lack cabling for internal SCSI HDD (which CZ-510C has). The internal connector used from the main board to the SCSI IO board is a non-standard 40-pin flat cable. The schematic for CZ-500C including the SCSI board can be found here.

The IO board itself is quite simple. Other than the connectors and ID switch, it just has a terminating 33oΩ/220Ω resistor network, a bunch of capacitors and a 1A fuse for the external power delivery. It is mounted on top of another IO board for the external floppy, and easy to remove with two screws.

If the SCSI board is not connected to the bottom PCB of the X68030, the system will not start.

External connectors

The external SCSI connector is a “Micro Centronics” connector, which is hard to find proper cabling for. It seems like the Japanese term for these are アンフェノールハーフ50 (Amphenol half 50) or アンフェノールハーフピッチ50 (Amphenol half pitch 50).

When looking for adapters to full-size Centronics, you can search for that in combination with アンフェノールフル 50 (Amphenol full 50), and look for a cable with a male Micro connector that goes to a female full size connector. This can then be hooked up to a Centronics Bluescsi device. Example from an Mercari auction:

There is a SCSI ID switch on the back of the unit. This doesn’t seem to be related to the external device, but rather the SCSI ID that the X68030 uses. Weirdly there’s also an option for this in SWITCH.X so I’m not really sure which option has priority. The compact version of X68030 does not have this switch, nor does other X68000 models as far as I can tell.


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Old Hardware Retro Computers

NEC PC-9801-86 Recap notes

Did a quick recap of my new PC-9801-86, and thought I’d add some notes to simplify for other people. There’s an earlier Japanese caplist here that I used as a base, but they used THT caps for the recap which I didn’t want to do.

Note that C33 and C34 are bipolar caps. The mouser links below link to the proper ones, but in my actual recap I just used polarized capacitors which seems to work as well (the Japanese link above did this too). It should be better to use bipolar caps though, so I might swap them later.

Purchase list

MouserAmount
710-8650904430058
710-8650603430033
710-8652306400041
710-8650903430055
710-8652503400032
710-86523044000132
710-8650606400012
647-UWP1C4R7MCL2

Cap list

PositionCapacitanceVoltageDiameterMouserNote
C133μF25V6.3mm710-865090443005
C233μF25V6.3mm710-865090443005
C333μF16V6.3mm710-865060343003
C40.47μF50V4mm710-865230640004
C533μF25V6.3mm710-865090443005
C733μF25V6.3mm710-865090443005
C847μF16V6.3mm710-865090343005
C910μF16V4mm710-865250340003
C104.7μF25V4mm710-865230440001
C114.7μF25V4mm710-865230440001
C124.7μF25V4mm710-865230440001
C1333μF16V6.3mm710-865060343003
C144.7μF25V4mm710-865230440001
C154.7μF25V4mm710-865230440001
C164.7μF25V4mm710-865230440001
C174.7μF25V4mm710-865230440001
C184.7μF25V4mm710-865230440001
C194.7μF25V4mm710-865230440001
C204.7μF25V4mm710-865230440001
C214.7μF25V4mm710-865230440001
C224.7μF25V4mm710-865230440001
C234.7μF25V4mm710-865230440001
C244.7μF25V4mm710-865230440001
C254.7μF25V4mm710-865230440001
C264.7μF25V4mm710-865230440001
C274.7μF25V4mm710-865230440001
C284.7μF25V4mm710-865230440001
C294.7μF25V4mm710-865230440001
C301μF50V4mm710-865060640001
C311μF50V4mm710-865060640001
C324.7μF25V4mm710-865230440001
C334.7μF16V4mm647-UWP1C4R7MCLBipolar cap
C344.7μF16V4mm647-UWP1C4R7MCLBipolar cap
C3533μF25V6.3mm710-865090443005
C3633μF25V6.3mm710-865090443005
C3747μF16V6.3mm710-865090343005
C3847μF16V6.3mm710-865090343005
C394.7μF25V4mm710-865230440001
C404.7μF25V4mm710-865230440001
C424.7μF25V4mm710-865230440001
C434.7μF25V4mm710-865230440001
C444.7μF25V4mm710-865230440001
C4547μF16V6.3mm710-865090343005
C4647μF16V6.3mm710-865090343005
C4810μF16V4mm710-865250340003
C504.7μF25V4mm710-865230440001
C514.7μF25V4mm710-865230440001
C534.7μF25V4mm710-865230440001
C5433μF25V6.3mm710-865090443005
C5533μF25V6.3mm710-865090443005
C564.7μF25V4mm710-865230440001
C574.7μF25V4mm710-865230440001
C584.7μF25V4mm710-865230440001
C594.7μF25V4mm710-865230440001
C6033μF16V6.3mm710-865060343003
Categories
Old Hardware Retro Computers

FM Towns SCSI boot guide

Had some issues getting SCSI CD-ROM booting working on my FM Towns tower, so thought I’d just do a quick step-by-step writeup on what I did.

The source of this is https://nfggames.com/forum2/index.php?topic=6821.0 but it’s very light on info, and took me a while to figure out how to get this on a floppy from a modern computer.

Hardware needed:

  • 3.5″ floppy drive + floppy
  • Greaseweazle setup
  • SCSI CD-ROM + cable for connecting it to back of FM Towns

Software needed:

Making the floppy

This is honestly the only tricky part, and the main thing is that the disk images are incompatible with greaseweazle as far as I can tell, so first you need to open Virtual Floppy Image Converter and convert it to a FM Towns compatible format.

  • Select “D88 format” as format and click the open icon to the left
  • Select FDMINI.BIN
  • This will then spit out a D88 image.

Connect your Greaseweazle over USB. Hook up the 3.5″ floppy drive to it. Use a twisted floppy cable. Run:

gw write fdimage.d88 --drive=A

This will produce the floppy you need

Booting

Connect the SCSI CD-ROM drive to the SCSI port at the back of the FM Towns and put a CD in it. Use the boot floppy and it will automatically boot from the external CD-ROM.

Works great!

Look at this chunky CD-ROM. So big and cool.

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Retro Computers

PC-9821 V13 modded to use ATX PSU

Just writing down some quick notes for converting a PC98 V13 to run on a ATX PSU. This is especially useful if you are in a 230V country.

These use essentially a AT power supply, with an additional 3.3V connector. This is apparently also used on some standard PC’s, see this page which describes it towards the bottom.

The PSU is the same size as standard “small” ATX power supplies, which is 150mm (W) x 86mm (H) x 140mm(D). For the replacement PSU, make sure to find something with suitable power placement to fit the holes in the case. Modern PSU’s will usually have different fan placement, so you might have to track down some older ones.

The V13 uses standard AT for the main two connectors except:

  • -5V is not populated
  • PG (power god) is not populated

This means that the cabling is as follows:

  • Black = GND
  • Green = 3.3V
  • Red = 5V
  • Yellow = 12V
  • Blue = -12V

I simply grabbed two AT->ATX power adapters and moved one of the AT cablings to free slots for 3.3V and GND in the ATX adapter. One GND pin is unpopulated, but that should be fine (and does seem to work well).

The (probably nicer) alternative is to simply remove the cabling from the original AT power supply and crimp ATX pins on those, to get the colors completely right too.

For power, rip out the original AT powr wiring and hook up the blue and white wires to PS_ON and GND on ATX. This will make the PSU work similar to the original one.

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Retro Computers

PC-9821 V13 Capacitor List for Recap

Did a full recap on my V13 PC-9821. Here is the cap list.
I did double check the values, but there’s still a possibility for errors, so I recommend checking them yourself too.

Motherboard

  • 1A2: 100u, 16v (6.5mm)
  • 1A9: 100u, 16v (6.5mm)
  • 1A10: 47u, 16v (5mm)
  • 1B13: 10u, 16v (5mm)
  • 1H1: 10u, 16v (5mm)
  • 1H2: 10u, 16v (5mm)
  • 1H3: 47u, 16v (5mm)
  • 1H4: 10u, 16v (5mm)
  • 1H5: 10u, 16v (5mm)
  • 1J3: 47u, 16v (5mm)
  • 1J5: 47u, 16v (5mm)
  • 1J6: 10u, 16v (5mm)
  • 2B5: 47u, 16v (5mm)
  • 2E1: 47u, 16v (5mm)
  • 2H7: 47u, 16v (5mm)
  • 2K3: 47u, 16v (5mm)
  • 3C5: 47u, 16v (5mm)
  • 3D1: 47u, 16v (5mm)
  • 3E11: 10u, 16v (5mm)
  • 3E12: 10u, 16v (5mm)
  • 5B1: 3300u, 10v (12.5mm)
  • 5B2: 47u, 16v (5mm)
  • 5C2: 47u, 16v (5mm)
  • 5M6: 47u, 16v (5mm)
  • 6F3: 10u, 16v (5mm)
  • 6N7: 10u, 16v (5mm)
  • 7F8: 10u, 16v (5mm)
  • 7J7: 10u, 16v (5mm)
  • 7K6: 10u, 16v (5mm)
  • 8G1: 47u, 16v (5mm)
  • 8J1: 10u, 16v (5mm)
  • 9D2: 47u, 16v (5mm)
  • 9D3: 10u, 16v (5mm)
  • 9E3: 10u, 16v (5mm)
  • 9F9: 10u, 16v (5mm)
  • 9G1: 10u, 16v (5mm)
  • 10B2: 47u, 16v (5mm)
  • 10D2: 47u, 16v (5mm)
  • 10F1: 47u, 16v (5mm)
  • 10G1: 10u, 16v (5mm)
  • 10K1: 10u, 16v (5mm)

Front IO Board

  • 1A1: 100U, 16V (6.5mm)
  • 1B1: 100U, 16V (6.5mm)
  • 1B2: 10u, 16V (5mm)
  • 1D1: 10u, 16V (5mm)

CBUS Riser

  • C1: 10u, 16V (5mm)
  • C2, C3: Unpopulated
  • C4: 47u, 16V (5mm)
  • C5: 10u, 16V (5mm)
  • C6: 10u, 16V (5mm)
  • C7: 10u, 16V (5mm)
  • C8: 47u, 16V (5mm)

The slots are 100 Pin 2×50 Edge connectors. 5mm between pin rows. Pin rows have 2.54mm spacing

Sound board

Component markings are super confusing here, but it has

  • 1x (near 1C14): 47u, 16V (5mm)
  • 5x (all the other ones) 10u, 16V (5mm)
Categories
Retro Computers

Sharp X68000 VRAM Repair

My X68000 (CZ-600C) was failing VRAM checks for Text RAM, and there wasn’t much info available about that online, so I’m writing some up here.

TL;DR information that is good to know:

  • On CZ-600C, IC1-IC16 is Text VRAM. IC17-IC32 is Graphics VRAM. All 32 of these RAM chips are on the Graphics sub-board.
  • The RAM IC’s used are MB81461-12 (32 of them).
  • Addressing for these can be found on the X68000 schematic. This will help narrow down which one is faulty, if you know the bad adresses.
  • Donor RAM IC’s can be found in Mega Drive units (two per unit).

Debugging the issue

Running MEMTEST (philly 1993) showed this error for TEXT MEMORY.

For more indepth understanding of the errors I ran Memtest68k which showed the range 00e725c – 00e725fc being bad, with Bits in Error Mask: 0000f000.

Looking at the technical guide for X68000 available here , this means that the error is in the last page of Text RAM, and the problematic bits are the highest 4 adresses. Looking at the schematic available on that page, this looked to be either IC16 or IC32 (turns out later it was IC16).

Addressing for Text and Graphics VRAM is slightly different, but the lower numbered IC’s map to the lower address ranges (as expected), and the data bus numbers for the pins in the schematic can help narrow down where the issues is.

To verify if it was IC16, I desoldered pin1 and pin2 on it, and wiggled them a bit while running memory checking. This produced more errors in the page of the already faulty range, which verified that it was indeed this IC that had issues. The main reason for doing this verification was that I was not sure if the first or last 16 RAM chips were for the Text part of VRAM.

After this, I was sure which part was bad.

Fixing the issue

Fixing the issue at this point was pretty straight forward, since it just meant swapping the bad part. Sourcing these are a bit awkward, but there are some available at aliexpress. I didn’t feel like waiting though, so I opened up my Mega Drive and grabbed the video RAM from that, since it uses the same IC’s. I’ll replace that later with the aliexpress ones, whenever they show up.

For desoldering these, you NEED a proper desoldering station/gun. I use a HAKKO FR301-22, but you can use cheaper ones as well. Overall, extracting this type of package is more annoying that DIP packages, but it worked out fine, with not messed up pads.

Removing RAM from Mega Drive

Next step is removing graphics sub-board and RAM chip from the X68000. Then just solder the Mega Drive RAM in the place of the bad RAM.

And there we go, memory test works now! All is good.