Help with OG X68000 ATX power supply replacement ( followed the nfg guide )

[zh97]

Hi, I have a Sharp X68000 that needs a power supply replacement.
I've followed the NFG guide on it at https://nfggames.com/nfg/x68repair/ .

A soft power circuit is required to use a modern ATX power supply,
and I've built one on a donut board with a 74LS04 chip and a 4.7k ohm resistor following the guide.
This being the first time in awhile that I've messed with building a circuit.
Am I wiring it up correctly?

The Power LED glows red but the soft power switch does nothing; the LED does not turn green.

Any help would be greatly appreciated!
The X68000 is too much of a beast to just leave as a display piece.
Mods please move this if it's in the wrong section.

https://www.turboimagehost.com/p/93370837/Screenshot_2023-09-09_at_2.03.26_AM.png.html
https://www.turboimagehost.com/album/281683/x68000_power_supply

[HIggy]

Hi.
That Image host is pretty nasty!
Anyway, you sure that the X68000 and ATX STB power are joined? Looks like a bit of a gap in the soldering there.

The other thing is being an OG X68000 you sure the main oscillator crystal is ok? What is battery area like?

Those oscillator crystals can look ok, but the battery acid gets pulled inside. That can give all sorts of weird behaviour. Can you take a photo of that PCB area?

Does the ATX fan come on?
Do you have a multimeter to check voltages?

[zh97]

Hi.
That Image host is pretty nasty!
Anyway, you sure that the X68000 and ATX STB power are joined? Looks like a bit of a gap in the soldering there.

The other thing is being an OG X68000 you sure the main oscillator crystal is ok? What is battery area like?

Those oscillator crystals can look ok, but the battery acid gets pulled inside. That can give all sorts of weird behaviour. Can you take a photo of that PCB area?

Does the ATX fan come on?
Do you have a multimeter to check voltages?

Apologies! It's the only image host I could find that didn't require creating an account to upload photos. Also use uBlock origin so I see zero ads

I did some troubleshooting with some tips from Facebook groups, reddit, this forum and your post;

1. Touching up my solder work on the small 74 circuit I built ( X68000 and ATX STB power )
2. Fully disassembling the machine and trying just the bare motherboard with nothing else connected
3. Removing the (already replaced) 3.6v nicad battery (measured at 1.5v with my multimeter)
4. Trying a different ATX power supply

The X68000 power LED now turns green and the hireso. (lution) red light turns on!

Sadly, pressing the power switch again causes the power LED to turn off but the hireso light remains red.
The main oscillator actually looks like it's been affected battery acid.
Do you know where I can source a reliable one? The old thread's CPPT1-HT0PT-ND has been discontinued.
I ordered one from a japanese website which may or may not work - will update how it goes.

Here are some images of the battery area on the PCB, the 74 circuit, and the machine's LED indicator lights
(unfortunately on the same image host)

https://www.turboimagehost.com/album/282251/x68000_repair_update

Will build a RGB-15 to VGA adapter next and test it to see if there's any video output!
Yes the ATX fan comes on now and I do have a multimeter.

[HIggy]

I think apart from floppy drive capacitors and battery area, OG X68000 are tough. Old style tech.

On your oscillator picture the visible pin looks to have classic acid crust/colour on it.

Regarding a replacement, on eBay there are chinese companies that sell crystals that they will program. Programmable DIP14 5v crystal? Sorry can't remember search term just at the moment

But I have gone down this route:
https://www.consolesunleashed.com/product/sega-master-system-dual-frequency-oscillator-mod-kit/

They do them for various systems, but the Megadrive and Master System ones will work. I think maybe SNES ones is also the same PCB footprint (DIP14).
You can't use PlayStation one as you need a 5v version. Whatever you get make sure it is 5v version larger size.

They are cheaper than eBay Chinese chip and you know what you are getting. The guy from Consolesunleashed can program it for X68000 frequency or you/I can with a Raspberry Pi.

I've fixed 2 OG X68000 using this method. I also replaced a couple of chips nearby, I can't remember which ones at the moment but they are cheap and worthwhile doing if other areas on the PCB are green looking from battery acid.

I think you are getting there and sorting the crystal should get you going