Goood day folks, I was wondering if anyone else has seen this? I have an MKS that constantly strip the earth leakage, I removed one of the earthing screws (The one near grid in) and the tripping has stopped but now the unit cuts off when connected to grid and slowly builds up from 9V to 270V on a 230V grid connection. I think I know what's happening here but not very sure and hoping for a little feedback if anyone has dealt with this yet... @Coulomb, you don't by any chance have experience with this yet?

13 hours ago, Psy said:

I have an MKS that constantly strip the earth leakage, I removed one of the earthing screws (The one near grid in) and the tripping has stopped but now the unit cuts off when connected to grid and ...

I'm totally not a fan of removing any of the earth screws. There are important capacitors that use that earth connection, and if you wire things correctly, you need the neutral to earth connection that the relay contact provides.

It may be that the neutral relay is stuck on; that could be awkward to test. I guess you'd have to power the relay, being careful to get the polarity correct so that you don't reverse bias the rest of the +12 V circuit. Then check that AC-out N no longer connects to earth (using earth near the relay, of course).

1 hour ago, Coulomb said:

I'm totally not a fan of removing any of the earth screws. There are important capacitors that use that earth connection, and if you wire things correctly, you need the neutral to earth connection that the relay contact provides.

Oh I totally agree, I have just found that I can use this to try diagnose better. Since the unit causes mains to trip with that in place this way I can get grid going and monitor the behavior for diagnostics. With the screw in it will not remain connected to grid and keeps causing the EL to trip... Because of this I now know the voltage drops to 0V and gradually increases until reaching the 270V mentioned, which is the part that is throwing me.

I know they had issues with the earthing contact a while ago after speaking to some of the folks that dealt with it, so that is possible considering the unit is a couple years old... so hearing it from someone else lets me know I have the right starting point. I'll try testing the relay and let you know how it goes!

9 hours ago, Psy said:

the voltage drops to 0V and gradually increases until reaching the 270V mentioned, which is the part that is throwing me.

is it really 270 VAC? Try measuring it on the DC range of a multimeter; it might be DC. That could be a big clue.

If it's really 270 VAC, then I'd suspect the resistor ladders leading to the voltage sensing op-amp. These are high value resistors (of the order of 600k to 1M), so a little moisture can throw them off wildly.

Ok so when trying to measure in DC the voltage is over 300V, I'll need a scope to confirm but I somehow doubt its putting out DC.I want to check that octo and the resistor ladder but we're closing today so I'll probably pick it up in the new year... I'll prolly return to this thread in Jan, hopefully I'll have the scope back by then. I always appreciate your feedback @Coulomb and hope to have some feedback for you soon 🤙