nfg.forums

Hey guys,

I have an X68000 Ace that stopped working.
Once I turn on the PSU the power LED turns red for half a second and then starts blinking green.

The original PSU was replaced with an ATX PSU using an adapter similar to this one:

https://github.com/mattsoft/X68K_EZ_Pico_PSU

The CMOS battery was replaced with a C2032.

I already read some articles here in the forum like

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

but couldn't figure out what's wrong yet.

The fan of the PSU starts turning once I turn on the PSU. So it seems it's getting started although the soft power switch is still turned of.

When I turn on the power switch the green light stops blinking and turns to static green.
But the computer won't boot.

I've  checked:

- 74LS08 - the IC is ok
- Q9 transistor - was ok, but I replaced it anyway
- C64 capacitor - was ok, but I replaced it
- 74LS244 - the IC is ok

I've also checked the low / high changes of the soft power switch at the 74LS08.

Then I checked the signals at the RP5C15. I measure the 32Mhz at pins 16 and 17.
The CLKOUT is at 1khz. Vcc is at about 5V.
The ALARM pin shows me a non static signal. I can't remember exactly, but I think it was a rectangle signal and it was at a static frequency (at least not a static low or high signal).

From what I've read all 4 signals at the 74LS08 have to get high for a system shutdown.

But what do I have to expect them to be when I

1) turn on the PSU?
2) then turn on the soft power switch?

Is it correct that the alarm signal is not a static high or low? I know that this pin can be used as timer or with a 1hz or 16hz pulse. But I don't know how it's configured in the X68000.

Any help is appreciated.

Best regards
Sascha

Hi Sascha, replace the variable capacitor next to the RTC chip, it goes bad over time. I had an Ace that it was a nightmare to get it going, but I noticed that it wouldn't "blink" the power when shutting down. It was the variable capacitor next to the RTC.

Hey amazin,

thanks, I'll check that capacitor.

Yesterday we interrupted the connection from the RTC Alarm to the 74LS08.
Since then the power on behaviour is as expected. Once the PSU is powered the power led turns red.
If the soft power switch is pushed it turns green as the PSU gets started.
The shutdown seems not to work yet. If we turn off the power switch the power led goes out instead of blinking green.

And we have another problem. The X68000 doesn't boot and we have a black screen.
The problem is that we get no proper VSYNC signal. The HSYNC seems to be ok, but the VSYNC is just strange. There is a signal, but the frequency jumps around.
As far as we could follow and measure the traces it looked like the Cynthia IC sends this strange VSYNC out.

Quote from: amazin on December 19, 2024, 04:52:05 AMHi Sascha, replace the variable capacitor next to the RTC chip, it goes bad over time. I had an Ace that it was a nightmare to get it going, but I noticed that it wouldn't "blink" the power when shutting down. It was the variable capacitor next to the RTC.

Do you have info on what's a good replacement value for it? Digikey or mouser component you used?

I read somewhere (Twitter) that a quick replacement is a 33pF ceramic capacitor, so I bought some, and it works. Also read that by doing that, the clock might run too fast or too slow, but like a second or so a day. I don't think it makes any difference in real life :-D