Martin Mac250 fault to earth?

[tonytech]

Good morning.

I'm looking for some wisdom regarding a pair of (old) Mac 250s.

They are on a 30ma RCD which has been reluctant to reset,

Portable appliance testing them shows a low insulation reading (0.1Mohms) and a high current leakage (10ma)

I found a pdf describing replacement of the "Phase compensation capacitor", but I dont think this would cause the fault I'm experiencing.

I've had no luck finding a service manual, so I'm turning to you.

My fault finding has been complicated so fay by discovering that the lighting bar the fixtures are on has a switched neutral rather than switched live. Grrrr.

 

Ta.

Tony

[Brian]

I found a pdf describing replacement of the "Phase compensation capacitor", but I dont think this would cause the fault I'm experiencing.

 

Ditto. It should have no connection to Earth so I'd start by looking elsewhere, specifically the mains input filter block. I can't remember if the output from the filter is on push-on spade terminals or is soldered. Try removing the output from the filter to the rest of the unit. So all you have in circuit is the input socket, the switch and the filter block.

[tonytech]

The power comes in on a euro socket.Line and neutral have short links to a pcb. earth has a slightly longer link to the chasis.

The pcb has a filter circuit, voltage selector, and frequency selector switches.

There are connectors to the transformer, a Relay (in one of the yoke arms) and a connector that I think goes to the lamp circuitry and two leads that go to the "phase compensation capacitor"

With the transformer, relay and lamp disconnected the fault clears.Measuring between earth and live with a ohm meter doesnt reveal anything, so I'm assuming a capacitor fault.

Hopefully I'll get further into it tomorrow.

T

 

 

[tonytech]

Just found the fault. So this is an update for my future self when I cant remember what I did.

On the back of the lamp holder metalwork, secured in such a way to require removal of lots of screws is one of those disc shaped thermal cutouts.

It is connected by two blue wires in a heat resistant sheath, The sheath had either not been installed correctly or had moved, because where the wires passed through one hole in the chassis the wires had chaffed through.

The bare wire was quite corroded, so the resistance didnt show on my multimeter, but did trip the RCD (or whatever we call them now)

 

Much obliged to all who helped, including by PM.

 

T