MG 10EE troubles

Greetings,

I have a 1943, serial number 24727 10EE.

Ran fine for years but it just started giving me trouble.


The attached contact is normally closed, but its jumped. It has continuity on both sides open or closed.

I can start the machine dialed down to it's slowest speed but if I increase the speed the mag coil cycles and breaks/starts the control circuit. (see youtube video)

video 151276469 - YouTube

If I disconnect the coil I can run the machine to full speed. Manually opening the contact breaks the control circuit without that cycling.

Thanks for any help.

Ray

DDYTDY said:

Greetings,

I have a 1943, serial number 24727 10EE.

Ran fine for years but it just started giving me trouble.


The attached contact is normally closed, but its jumped. It has continuity on both sides open or closed.

I can start the machine dialed down to it's slowest speed but if I increase the speed the mag coil cycles and breaks/starts the control circuit. (see youtube video)

video 151276469 - YouTube

If I disconnect the coil I can run the machine to full speed. Manually opening the contact breaks the control circuit without that cycling.

Thanks for any help.

Ray

Click to expand...

The relay that you’re having trouble with is the anti-plugging relay (AP), in the middle of the panel at the top. If it is tripping before the forward/reverse contactor opens, your problem is most likely the E-B resistor at the top, right of the panel. The three resistors are a common failure point (actually the only real problem that I'm aware of) for the square-dial DC control panel.



The AP relay is supposed to release at about 300 RPM. Its function is to keep you from "plug reversing" the machine at high speeds; that means to reverse the current to the armature in order to rapidly change spindle direction. When it's closed it provides the current to allow the forward (F) or reverse (R) contactor to close. Once it opens, the coil on the F or R contactor is kept energized by the E-B resistor. If the resistor is open the machine will do exactly what you describe.

It’s a good idea to replace all three resistors. Here’s what I normally recommend:

• Ohmite L50J2K0E (2000 Ohm, 50W, 5%) Newark #64K5003
• Ohmite L50J3K0E (3000 Ohm, 50W, 5%) Newark #64K5013
• Ohmite L50J200E (200 Ohm, 50W, 5%) Newark #64K5007

1600 Ohms isn’t a standard size; the series combination of the 3000 and 200 Ohm resistors take the place of the two 1600s. The resistors are overrated by a factor of about 10, so you shouldn't have any problem with them again. (The wattage was chosen based on the physical size; the overrating is a bonus.) Newark usually has them in stock for about $10 each. The 2000 Ohm resistor is currently out of stock, but Digikey has it (link). Digikey and Mouser, are also options for the resistors.

Cal

Thank you very much!

It all makes sense now. (or it least more of it)

I love this old machine.

Regards,
Ray