Summary
- My X68000 ACE HD’s power supply was not working.
- Recapping was not enough to fix it.
- Repalced a Zener diode, a transistor, and a voltage regulator to fix.
My friend gave me an X68000 ACE HD and mentioned that it doesn’t power on. X68000 is a 30 year old computer and the capacitor leakage is a very common problem.
In fact, the X68000 ACE HD seems to have severe capacitor leakage in its power supply.
I’ve replaced all the capacitors of the power supply with the brand-new Nichicon caps. However, the PSU didn’t work.
Sharp made the service manual of X68000 freely available (though you need to purchase it at 0 yen on their Japanese e-book site - you can also find it on Archive.org), and the schematic of the power supply is in it. I’ve also learned that a zener diode (ZD31) is often broken. I’ve ordered two Zener diodes from Mouser.
- Zener Diodes 6.8V 0.5W for ZD31 (BZX79C6V8)
- ZD51 zener diodes.
Some days later, I’ve received them and replaced them. However, it still didn’t work. I’ve checked other components around and I’ve found 2SC1815 (Q32) might be faulty as well. I’ve ordered it too. (2SC1815-GR PBFREE)
By replacing the Q32, I got +5V output now. I’ve also got -12V, but it seems like +12V is not coming out and got 0V reading.
I’ve measured IC22(S13122V) and the Vin was +14V. However, the output was only 0.3V or so. It should be around 12V. So, I’ve ordered a S13122V from ebay. It costed $10.65 (including shipping).
I’ve removed the old 3122V and tested with my multi-function tester. I’ve confirmed that the voltage regulator is broken.
I’ve soldered the new 3122V.
Then, I’ve tested the PSU and I’ve got 12VDC successfully.
Now, the X68000’s power supply is fixed!