Trouble getting ][FX to start

[papa_november]

I recently found a Mac ][FX. It looks like it's been upgraded from a Mac ][, as it has a Mac ][ case badge but a ][FX motherboard inside. The machine has 8MB RAM and a 500MB hard drive with MacOS 7.6 installed.

Anyway, it works fine but it's really hard to turn it on. More often than not, pressing the power button on the keyboard (or the power button on the back) won't turn it on. I have to leave it unplugged for roughly 10 seconds and then plug it back in again before it'll turn on. Any idea what's going on here? I've checked the PRAM batteries with a multimeter and they seem to still be OK. I've also swapped in a couple of different batteries.

Another problem is that it won't turn off properly. When I choose "shut down" from the Special menu I get the "you may now switch off your macintosh safely" screen when it's supposed to just switch itself off. How do I make it turn off properly?

 

[Big Bird]

This is a fairly common problem we've seen with the power supplies in Mac II-series machines. See my recent discussion in this thread. In my personal testing, I've isolated to problem to not include capacitors, fuses, batteries, motherboard problems, etc. Rather, the relay units on the power supplies themselves often fail to function properly with age, becoming either sticky or refusing to make contact altogether. In your case, that's very likely what's causing the machine not to shut itself down automatically: the relay fails to disconnect even after the power off instruction is issued.

I have found, in my extensive work on some IIsis, that often the connector from the PSU to the logic board gets corroded and prevents the power supply from making proper contact. Plugging and unplugging it REPEATEDLY will often solve the problem, but in particularly tricky cases, a straightened paper clip and perhaps some rubbing alcohol is useful to scrape out the inside of the connector holes. This solved an issue with a couple of power supplies that appeared completely "dead" and/or refused to soft power off.

However, your startup issue sounds more like the issues commonly noted with the IIcx/IIci/Q700 series PSUs, as described here. There have been mixed reports of fixes, but I am unfamiliar with the II, IIx, IIfx power supply personally. Perhaps someone else here has more direct, hands-on experience?

Also, equill points us to this very helpful page on which you can find schematics of some of the II-series.

 

[equill]

... it works fine but it's really hard to turn it on ...

Although the Mac II uses a 661-0375 PSU and the IIfx a 661-0542, it's possible that this is more relevant to the shapes of the cases than the electrical design. The difficulty probably lies in the 5V TRKL supply from the PSU, which is present while ever the Mac is attached to the mains supply, and which is necessary for startup.

... I've checked the PRAM batteries with a multimeter and they seem to still be OK. I've also swapped in a couple of different batteries ...

Only one of the batteries is concerned with PRAM settings, but both should be 3.3V or more in circuit, and certainly replaced before they reach 2.8V. Shutdown depends on the same TRKL supply's having already fallen to less than 1V when the command is given. You don't usually see the message 'You may now ...' because it is either circumvented or too fleeting when correct shutdown occurs.

... Another problem is that it won't turn off properly. When I choose "shut down" from the Special menu I get the "you may now switch off your macintosh safely" screen when it's supposed to just switch itself off. How do I make it turn off properly?

One of my IIci Macs starts correctly with soft power, but declines to shut down in the same manner as your Mac does. Apple's Service Source says to change the power supply. 15-odd years later you live with the fact, or adapt, or try the PSU repair here.

The PSUs of the IIcx, IIci and Q700 are identical (661-0467), although the Astec units fail in the TRKL circuit more often than the Delta PSUs. Failed units can be started as you have done, or by 'bumping' (a quick off and on again with the mains supply switch), or perhaps (if you can verify that the same sawtooth oscillator circuit as in the IIcx &c. PSUs is the cause) by the repair cited.

de

 

[papa_november]

Thanks for the tips! I can't seem to find a replacement power supply around here, and I don't have time to trace out the soft power circuit. I was thinking it might be possible to just stick an ATX power supply with a similar wattage in there, but unfortunately I can't find enough time for that either.

 

[pee-air]

Thanks for the tips! I can't seem to find a replacement power supply around here, and I don't have time to trace out the soft power circuit. I was thinking it might be possible to just stick an ATX power supply with a similar wattage in there, but unfortunately I can't find enough time for that either.

It would be a lot easier to use an AT power supply. An ATX power supply would require shorting two pins on the connectors in order to power on your IIfx.

 

[Unknown_K]

An AT/ATX PS wont fit in a IIfx, a Mac II/IIx/IIfx supply is not that hard to find and get shipped (try LEMSwap).

 

[pee-air]

An AT/ATX PS wont fit in a IIfx, a Mac II/IIx/IIfx supply is not that hard to find and get shipped (try LEMSwap).

That is correct. However, looking at the book "Build Your Own Macintosh & Save a Bundle" you could use an AT power supply in a PC case with very little dickering. An ATX power supply would require shorting two pins on the ATX power supply, and everything I've read advises against that.

If you want to keep your IIfx in the Apple case, you will have to do as Unknown K suggests.

 

[papa_november]

I managed to find another power supply. It doesn't work right either, but it does work a lot better. It's much easier to get it to turn on (just leave it for a minute after plugging it in and it works every time), but it rarely turns off properly. The old PSU is a Sony, and the new one is an Astec.

For the record, an ATX PSU can be made to fit, but it would have to be a mini-ATX PSU. It also would have to be stripped from it's housing and jammed into the old PSU's housing. The only real problem with getting it to work would be the soft-power circuit, which is probably very different from what the Mac uses.