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Macintosh Plus 1MB trips RCD Fuse

DrAlis

Experienced Member
Joined
Nov 11, 2021
Messages
134
Dear Expert, as per title my Mac Plus works fine in principle but even when off: After a while my house's RCD fuse blows. I think in Germany they fire at 30mA. I have no idea where to look. So how the hell is there a leak to shield pre power switch? Puzzling because it does this while off also. Any ideas?
 
Thanks, these RIFAs are a weak point. But would them failing not cause a short? Are they connected to neutral not negative? I feel this is a dumb question... I think this is a great place to check. But I also feel this is dumb design that a faulty component can cause harm while the device is off.
 
Capacitors have numerous failure modes that can cause all sorts of different problems.

They can fail open, short, lose capacitance, become electrically leaky and turn into a variable resistor.

The reason a bad RIFA would trip an RCD/GFCI is because it's connected from mains to ground. If it goes bad, it's effectively shorting the mains to ground, which results in spiciness.
 
Thanks, I will hunt for the RIFAs and caps. I will recognize the RIFAs, not sure how to see which caps are the filter ones. For science: I am still a little curious why it takes between 1min and 2h for the RCD to fire... I guess the cap is warming up and then at some point leaking in excess of 30mA. The irregularity is strange though. I will report after I do the fix. This might be a while since getting spare electronics (Germany) I am not familiar. Running without the Rifas and Caps is not advised, right? I got around 10+ vintage machines on that power socket branch and afraid I will deteriorate my own power quality... Thanks!
 
You can generally run a power supply without the RIFAs, just with reduced safety and increased transient noise from the supply. You cannot run a power supply without any of the normal capacitors. If you power on a supply without the capacitors, at best nothing will happen, at worst the power supply will blow up/die from the mosfets being spiked.

The RIFA capacitors should be substituted with modern X2 or Y capacitors, depending on where they are in the circuit.

As for places to buy components: Mouser or Digikey, last resort Ebay or Ali Express.
 
I like Mouser, I order enough to get free shipping, My last order from Mouser UK was shipped from Germany and my previous order was shipped from the USA and received in 3 days, Never used Digikey though i do buy the odd bits and bobs from ebah.
 
You can generally run a power supply without the RIFAs, just with reduced safety and increased transient noise from the supply.

Safety ?, Not sure about that.

They are very low farad value caps to short high frequencies to earth. Reduces the transmission of the switching frequencies out of the device to your RF devices, but as most are digital these days, they are generally not needed any more.

What would be their safety duty ?
 
They are also there to make sure no noise it send back to the power grid. In Germany (where he's apparently from), it's in fact forbidden to run a device with those caps removed. Not that anyone will knock on your door and check, well - unless the device causes interference not limited to the direct place of usage.

They are *not* for safety! Their usage actually introduces additional danger for people of getting shocked, which is why they have very high standards to fulfil.
 
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You will probably have class X and class Y RIFA "safety" [sic] capacitors in your power supply.

Class X are wired from Live to Neutral whereas Class Y are wired from Live to Earth and Neutral to Earth.

You may also not be able to detect the RIFA capacitors themselves if you have an IEC connector on the machine. Sometimes they are built into the IEC chassis mount connector.

Your mains protection device may not only be looking for earth fault currents - but also an imbalance in the currents flowing in the live and neutral conductors. If there is an imbalance, the current is flowing somewhere it shouldn't...

Dave
 
Your mains protection device may not only be looking for earth fault currents - but also an imbalance in the currents flowing in the live and neutral conductors. If there is an imbalance, the current is flowing somewhere it shouldn't...
This is exactly how US GFI breakers operate. Not sure about EU.
 
We have two different types. It depends what is fitted. However, the UK is not part of the EU anymore, but let's park that discussion shall we!

Dave
 
If you plan on replacing the RIFA caps or recapping the board, I had good luck with console5.com. They sell recap kits (for axial, radial, and tantalum caps), and replacements for RIFA caps.
 
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