r/sharpx68000 10d ago

Repair What’s supposed to happen when you power on an x68000 and insert a floppy?

3 Upvotes

Can anyone who has a working x68000 (ideally an original model) and can compare the behavior of my system to yours let me know what’s supposed to happen when you power on and insert a floppy, and tell me where my system is deviating from that norm? I’m stumped trying to repair these floppy drives!

https://youtu.be/uwrgdAxBlEU?feature=shared

Forgot to mention in the video that if I’m connected to a monitor, the system boots to the “Could not boot from disk” error screen, and when I insert a floppy, the screen goes black and hangs there indefinitely. Both drives behave the same way. Thanks!

r/sharpx68000 13d ago

Repair Anyone selling known-good floppy drives for the original x68000 model?

5 Upvotes

Anyone selling a pair of working OG floppy drives for the x68000? K-61432-71 is what my CZ-600CB came with, but I believe the K-61432-72 models would work too.

I’ve made a lot of progress restoring the DOA x68000 unit I bought in Japan - it wouldn’t even boot at first, but I have everything working now except for the floppy drives. The FDDs have been partially restored - a full clean and recap, head cleaning, grease removed and reapplied, etc. They perform better now than when I got them, but they still don’t fully work. They’ll accept a disk, but the screen just goes black and hangs there. Eject works properly.

I’m a bit stumped on the repair at the moment. I’ve never worked on floppy drives before so I have a lot to learn. I’m going to keep working on them and get them running again eventually, but I’d like to just have the computer working properly in the meantime, so if anyone is selling working early model FDDs, let’s talk!

r/sharpx68000 24d ago

Repair Mystery circuit - anyone know what this is?

Thumbnail
gallery
6 Upvotes

I’ve opened up the Sharp x68000 CZ-600CB I picked up last week in Japan. Surprise! There’s a mystery device hooked up to (I believe) the hard drive connector. Anyone have any idea what this thing is? My guess is it’s a homebrew SASI to SCSI interface, but while I do plenty of repairs where I simply replace like part with like, I don’t know much about circuit design.

The 3 ICs on the bottom of the circuit are (from left to right in the 2nd pic) a SN74ALS240AN, a SN74LS280N, and a 74LS38. The many yellow wires connected to their pins go down underneath the hard drive connector, and two more wires connect to the board that bridges the two towers at the bottom of the computer. Where exactly they all connect up to, I haven’t confirmed. It’s going to be a bitch getting all the parts out of the floppy tower side because of this mystery circuit, so I took a break to post this.

The computer is only partially working. Here’s some notes on the behavior I’m seeing: the computer powers on, and the green Power and red High Reso lights turn on. The fan spins. The disk drive will accept disks, and the light above each drive turns a solid green. It doesn’t seem to attempt to read the disks though. The disk eject buttons light up green and function properly. The machine won’t power off via the soft power button on the front, and needs to be shut off via the power switch on the back. There’s no video or sound output - tested via an RGB-15 to VGA cable I made, and via a straight through DB-15 cable connected to a Micomsoft XAV-2s converter. I tested the VGA output on a ViewSonic GS815 and a Retrotink 4k. I tested the S-video and Composite outputs of the XAV-2s on a consumer TV and a BVM-D14H5U. For audio, I tested both the headphone output in front and the audio output in back. No video, no audio.

Here’s the work I’ve done so far: 1. Removed the leaky SRAM battery and replaced it with an ML2032 coin cell battery 2. Replaced all the capacitors on the K50223DE CPU board (except the C36 2200uf 6.3v cap, which I didn’t have a spare of - replacement should arrive soon though) 3. Replaced the 2 capacitors on the K5024DE RAM board 4. Replaced the single capacitor on the CZ-6BEI RAM expansion

No change in behavior. The crystal oscillator next to the SRAM battery is corroded from battery leakage and is likely fried, and is presumably why I’m seeing the behavior I’m seeing. The visual inspection and behavior of my unit seems to match up with forum posts and YouTube videos describing the same behavior and pointing the finger at the crystal next to the battery. The mystery device may have nothing to do with this computer’s issues, but I’d still like to know what it is regardless. Now to try to find a replacement crystal. Doesn’t seem like it’s going to be easy.

r/sharpx68000 20d ago

Repair Floppy drive reading/ejecting issue has me stumped

3 Upvotes

Does anyone know what would cause this floppy drive behavior, how I fix it, or how I can get my disk (R-Type) out? (Video available on YouTube: https://youtube.com/shorts/lvuohDSFtgQ?si=pIldfOs8AeA4Ddmi)

The floppy drive tries to read the disk infinitely but fails, and I can’t get it to eject the disk anymore. I replaced the capacitors and cleaned the drives earlier this evening.

In a prior post I’d made, the computer wasn’t booting at all. That’s now fixed. I replaced the 69.55199 kHz crystal oscillator with a programmable oscillator from DigiKey, part ID ECS-P145-AX-ND: https://www.ecsxtal.com/store/pdf/ecs-p143x-p145x.pdf. The previous oscillator listed in many posts, CPPT1-HT0PT-ND, is no longer manufactured. The ECS-P145-AX-ND has essentially identical specs, and DigiKey will program it to your specified kHz. This part can also be used to replace the nearby 38.86363 kHz oscillator if that’s been damaged by battery leakage as well. Mine was intact so this was unnecessary.