Levin Lathe DC Motor Controller Diagnostic Help Needed

Good Day All.

I am working on a vintage Levin Lathe, the literature suggests 60's era, though these are still produced. The machine is a "precision instrument lathe" The machine has a DC motor underdrive headstock, with its own variable speed controller, reversing switch, and foot pedal control.

The machine has as an accessory, a table mounted DC motor with its own variable speed controller,reversing switch, and the same foot pedal control (wired to both controllers)

ISSUES:
1) The foot pedal switch does not operate the accessory drill motor, controller and motor works when jumpered. The foot pedal does work the underdrive, and appears connected (did not test yet)
2)PRIMARY ISSUE, the drill accessory motor will only run in reverse (when the foot switch is jumpered as above).

Thankfully, I have schematics for the machine, I will attach pics, but I'm still having trouble with diagnostics. I am trying to use a multimeter to learn how the controller works, to track the forward run problem. However, I am unable to get continuity from power in, to any wires going to the motor when it is in a condition that I know it runs, aka reverse, with foot switch jumpered. In my mind, if I can't do this, then I can't work backwards. Oh, the Fw/ rev switch tests out OK with continuity test.I haven't tried to test anything under power.

Is this due to the mechanical electro switches in the controller? I can hear and see them operate when I'm working the power and/ or reversing switch.

Any advice?

Additionally, I have schematics for the other controller if you own a vintage Levin yourself, just hit me up for a copy.

Can't help with your problem, but want to say "Hi." At least I do know something about your lathe and the drilling tailstock. The Levin I run is a 1950's open headstock D model with a replacement series-wound motor and an SCR foot speed control. I have some of the round head and flat top lathes and Levin OEM motors and controls, but none are set up to run yet. I have a lot of Levin and Derbyshire and similar lathes and accessories.

I do have a Minarik controller and a shunt-wound motor I adapted to run a Derbyshire Magnus lathe many years ago, so I once knew a little bit about the Minarik drives.

Larry

The relay marked "RL2" on the schematic is the reversing relay. If it is operating OK, then either a contact is not good, or else maybe a wire is broken. The relay in the control schematic you show is just reversing the voltage to the armature. If the motor runs reverse, it should run as well forward, and it seems that you have confirmed that.

So check for loose wires or bad contacts in the relay.

The speed control per the schematic is just a variac type device changing the armature voltage.

JST said:

The relay marked "RL2" on the schematic is the reversing relay. If it is operating OK, then either a contact is not good, or else maybe a wire is broken. The relay in the control schematic you show is just reversing the voltage to the armature. If the motor runs reverse, it should run as well forward, and it seems that you have confirmed that.

So check for loose wires or bad contacts in the relay.

The speed control per the schematic is just a variac type device changing the armature voltage.

Click to expand...

Wow, thank you for the advice.
I've not had the chance to look, but I will.

What I did notice was the relay that you speak of (I think) is mechanical, and made of clear plastic. I can both see and hear this contact switching on and off with BOTH the on/off switch (when in rev), and the fw/rev switch. I will use your info to investigate further

QUESTION. Why can I not get continuity between power and anything that feeds the motor, I would assume power to the field when operational, so continuity should be there in a running state, but without power??

Love the forums, thanks everyone. Again, happy to share better copies of these schematics if you need them.

QUESTION. Why can I not get continuity between power and anything that feeds the motor, I would assume power to the field when operational, so continuity should be there in a running state, but without power??

Click to expand...

Is S02 the connector to the pedal? It looks to me like when in forward mode both relays should on at the same time. When in reverse only Relay one should be active.

Do you have a schematic for the pedal? It looks to me like they're feeding 110v AC through the pedal when in forward or reverse. I wonder if there's another rectifier in the pedal assembly? Because relays need DC, feeding 110 AC to S02 implies that DC has to be coming back to activate the relay. Relay 2 looks like it has its own diode + RC to make DC.

scooternut said:

....

QUESTION. Why can I not get continuity between power and anything that feeds the motor, I would assume power to the field when operational, so continuity should be there in a running state, but without power??

.....

Click to expand...

Many meters will not read resistance through diodes, because the meter uses a very low voltage to read resistance, and it is less than the voltage drop through a silicon diode (rectifier). With a Fluke meter, switch it to the setting marked with a diode symbol, and it should read through OK. In that mode, the reading is the voltage between the probes, so it will likely show a diode drop of around 0.65V or so from the line to a motor wire. With high current diodes, the drop may show less. For a selenium rectifier, the reading will be much less than for a silicon rectifier.

A funny thing happened on my way to being frustrated with this.

I finally get some time to get back in and stare at this controller for awhile, following wires and trying to make sense of it. AT one point, I'm just staring at it, then suddenly, out of nowhere, the other relay clicks and the motor starts spinning! Maybe something just needed to warm up a bit.

The foot switch is working as well after some quick attention to the contacts. I believe that all functions of the lathe controllers are working properly now. Very neat old piece of machinery.