Weird iMac/RCD problem - any ideas?

[Dick Smith]

I have a weird problem with an iMac (G4).

The machine is 'pre-owned' by my son in the USA and he sent it over to the UK for me to take to France.

When I plugged it in (in England to try it out) it tripped the RCD on the consumer unit, but not the MCB.

I have taken it for a diagnostic at an Apple service workshop, and they found it OK, it didn't blow their circuits and it passed the diagnostic perfectly.

I tried a new power cable, same result, also trying different power sockets (including the dedicated microwave socket).

I have seen on a sparkies' forum that damp in a socket may lead to an earth leakage which might cause this to happen, but if that is the case, why should it only be this appliance that causes it. Microwaves, dishwashers etc must draw much more power.

Could it be that as the computer is dual voltage there is a sudden spike in the split second during which it decides which voltage it is receiving and it is that transient spike which causes the trip?

Any sensible ideas very gratefully received.

[Anton Redman]

Possibly a cheap UPS might provide enough of a buffer to get the machine running steadily. Maplin now have then at £30  so not a vast spend if the computer is a door stop without it.

Might be work taking the back off and checking for chaffing of the wires and dust. I have not taken an Apple to bits since an Apple III. Last article I read on the subject made DIY Treplainning sound easier.  

[Dick Smith]

Thanks, Anton - but what is a UPS (apart from them that delivered the thing!) - is that a smoothed power supply? I'm getting one today to see if it will work.

Unfortunately it's the lampstand type,

[IMG]http://i50.photobucket.com/albums/f338/dick_at_aulton/150px-IMac.jpg[/IMG]

and you need a specialised toolkit to work on it - but No2 son reckons it was fine when he checked it out, so it is looking as though it is something in the house. We also blow the RCD when a lightbulb goes...

[Dick Smith]

Have now found out what a UPS is. Might well be the answer if I'm right about the transient resistance. My only concern is that it blows the RCD before I switch it on.

[Nick Trollope]

It is bound to be the switch-mode power supply in the machine - more likely as, as you you have surmised, because it is an auto-voltage-switch type. The power switch doesn't actually switch the mains, it just causes the power supply to "start".

Switch-modes are very "capacitative" and will cause huge (short) current draws. Your modern RCD is sensitive & quick & will trip. An ONLINE UPS (must be online, as an offline UPS is only connected when the mains fails - you won't get one for 30 squid, I'm afraid) will fix your problem (well, computer one at least). Other possible solutions a) A surge-protect plugtop or extension lead (which should work backwards, they just have inductors in series, which effectively work the other way around to a capacitor) b) never accept gifts from your children - there are usually conditions attached c) get a PC d) hold the RCD up whilst you switch on e) etc e) etc etc.

 

[Dick Smith]

Thanks, Nick, I'll take notice of everything except c).

What concerns me is that I have now used about 15 Macs on this circuit (plus a couple of PCs) and never had this problem. I have a surge protected power cable here, but I think I'll hold off and get a proper one, as you advise.

Actually, there were no conditions to this at all. He had bought the latest one (he gets a VERY good staff discount) and his wife wanted the old one out of the house!

We are also getting the house wiring checked!

[Anton Redman]

Two comments

The world of solid state electronics continues to move on. I cannot believe how little heat solid state inverters produce / how little energy they waste I would still have a look at a cheap UPS.

If I had space in the Tableu d  Electricite in my French House for a bi pole fuse holder I might run a fused cable to one socket for exclusive use of the Mac assuming I did not have to wreck any decoration in the process.