Help - 1943 mg stopped working - rpc buzzing loudly

Hi Everyone!

I am running (or at least was until recently!) a 1943 round dial MG Monarch which I have enjoyed using (although not really pushing it to its limits at all. mainly aluminum and brass)

A few days ago I used the lathe normally and shut it down normally. The next time I went to use it, there is a very loud buzzing noise coming from the RPC I am using to power it (and of course it wont start).

I first thought it may be contactor noise and opened the back contactor cover.. on pressing the lathe start button, the main contactor is closing.

The rotary phase convertor is a WNY RPG07 .. says 7.5Hp on the panel cover.

The volts at the main contactor on the back of the lathe on the 3 inputs are 120, 121 and 253.

In trying to locate the sound, it seems to be coming from the RPC convertor panel.. I located that by using a screwdriver as a stethoscope on the panel cover.

In using this lathe with the RPC on previous occasions, starting it always had a second of this buzzing (almost sounds like chattering-NOT a hum), followed by the lathe starting. Now, I just have the buzzing..

Could someone give me some pointers in how to diagnose and solve this problem please?

Pull the cover on your rpc panel, take some pics so we can see whats going on. Bob

jiminy said:

Hi Everyone!

I am running (or at least was until recently!) a 1943 round dial MG Monarch ...

A few days ago I used the lathe normally and shut it down normally. The next time I went to use it, there is a very loud buzzing noise coming from the RPC I am using to power it (and of course it wont start).

I first thought it may be contactor noise and opened the back contactor cover.. on pressing the lathe start button, the main contactor is closing.

The rotary phase convertor is a WNY RPG07 .. says 7.5Hp on the panel cover.

The volts at the main contactor on the back of the lathe on the 3 inputs are 120, 121 and 253.

In trying to locate the sound, it seems to be coming from the RPC convertor panel.. I located that by using a screwdriver as a stethoscope on the panel cover.

In using this lathe with the RPC on previous occasions, starting it always had a second of this buzzing (almost sounds like chattering-NOT a hum), followed by the lathe starting. Now, I just have the buzzing..

Could someone give me some pointers in how to diagnose and solve this problem please?

Click to expand...

Normally you start the RPC, get the idler motor running, then start the 10EE. It sounds like you have the idler motor starting up simultaneously with the 10EE. There's no reason to do that and it puts extra load on the starting capacitors. You do have an idler motor connected to the RPC, correct?

The buzzing is probably from the relay in the RPC control box (usually a potential relay) which controls the starting capacitors. It's job is to disconnect the starting capacitors from the idler motor as soon as the voltage on the motor comes up. Starting capacitors can't handle continuous operation and may burst if left connected too long.

Cal