Nova Mercury Mother Board Problems

[JOHN KARTCHNER]

I have a Nova Mercury Minilathe with the 1/2hp 380 WATT DC permanent magnet variable speed motor. The mother board has gone out, but from all indications the motor is still good (new brushes installed). Teknatool is no longer supporting this lathe and has no suggestions for a replacement control box. I'm unhappy with them because I am fond of this lathe. Do any of you electronically endowed geniuses have an inexpensive solution for an electronically challenged Spanish Literature professor? (Friendly comments require an embarrassing confession: the motor was running erratically and Tim Gist suggested a threaded button on the motherboard with which I could fuss. The fussing was successful except the my digital enthusiasm exceeded the strength of the thread. The new tech in Florida says I need a new motherboard, which, as I originally stated, is no longer available.)
John Kartchner

 

[Gynia]

The controllers for these small DC motors tend to fail by a component over heating. If you look at the controlled board you will likely see a burned part or parts. If you replace the burned part you could be back in business. You could replace the controller with another controlled. But the controllers are usually setup for a particular motor and a particular application. Adjustments can be made and components can be changed to make a controller more suitable for the woodturning task. That would be beyond the comfort level of a Spanish teacher.

Your best bet is to get a replacement motor and controller which is made as an upgrade for the more popular mini lathes and rig it to work with your Nova.

John Lucas has a mercury which he is fond of and he will likely be able to provide better advise. You might want to e-mail him directly on the matter.

 

[Bill Boehme]

While it is possible to have a failed part look burned, it is highly unlikely if the bad part is a solid state device. They typically go too fast to leave any telltale signs of overheating.

Perhaps you can describe any symptoms prior to its failing that might possibly point to a culprit. Very likely parts to fail include fuses (since their only purpose in life is to fail), switches, connectors (circuit card connector or any other connectors), loose wires, bad power plug, and potentiometers (that is the device on the other end of the speed control knob).

Was there any erratic or sluggish behavior or anything else out of the ordinary before the lathe quit running? If it failed suddenly, did that happen immediately after something was done to the lathe (new brushes installed, motor stalled when turning caught on toolrest, major catch, spindle lock engaged, etc)?

When you turn the power on now, does anything happen such as lights coming on, something humming, smoke curling up from something, sparks flying or whatever?

Since the motor is a DC type, it probably has vents and an internal cooling fan which means that it can get clogged with dust and shavings -- leading to overheating and possibly burning out. Could this be a possible scenario?

Generally, a failed component on a PWB (printed wiring board) is the last thing that I would suspect. If a component on the board fails, it is almost always because something else that isn't working right caused it to fail.

 

[Alan Trout]

John,

I met this guy one time. They are in Austin and say they can fix just about any board. It might be worth contacting them. http://www.fixyourboard.com/index.html I ask him if they would fix other types of boards and he said yes. That was a year or so ago so I don't know if it is still that way but worth a shot.

Good Luck

Alan

 

[Bill Boehme]

... (Friendly comments require an embarrassing confession: the motor was running erratically and Tim Gist suggested a threaded button on the motherboard with which I could fuss. The fussing was successful except the my digital enthusiasm exceeded the strength of the thread. The new tech in Florida says I need a new motherboard, which, as I originally stated, is no longer available.)
John Kartchner

John, it is best if you add additional information at the end of the thread because revising your original post is very likely to be overlooked as well as confusing to those reading it for the first time.

I almost missed your additional information because I was looking to see you had a follow up to any of the responses. Can you explain what you mean by "threaded button"? I am an electrical engineer, but the only thing that term conjures up in my mind is something like a button on clothing. Are you saying that you unplugged or broke something off the circuit board? Can you describe the erratic behavior of the motor?

 

[ray hampton]

Bill, how hard is it to buy new components for each PCB and replace every parts on the board ?
when a company stop producing a certain tool, what will happen to the excess service parts ?

 

[john lucas]

john I have a used powersupply from a Jet mini variable speed lathe. It reads from 90 to 160volts and used on a 1/2hp motor. You are welcome to it if the electronics guys here think it will work on your lathe.

 

[JOHN KARTCHNER]

John, it is best if you add additional information at the end of the thread because revising your original post is very likely to be overlooked as well as confusing to those reading it for the first time.

I almost missed your additional information because I was looking to see you had a follow up to any of the responses. Can you explain what you mean by "threaded button"? I am an electrical engineer, but the only thing that term conjures up in my mind is something like a button on clothing. Are you saying that you unplugged or broke something off the circuit board? Can you describe the erratic behavior of the motor?

The motor would spit and sputter then roar. The little button or post had a phillips head so that it could be twisted one way or the other. Fussing with it had a positive effect on the motor, but unfortunately I broke it off and no amount of my "fixing" would return it to functionality. With the circuit evidently broken, the motor will not respond to the on/off switch.

 

[Bill Boehme]

The motor would spit and sputter then roar. The little button or post had a phillips head so that it could be twisted one way or the other. Fussing with it had a positive effect on the motor, but unfortunately I broke it off and no amount of my "fixing" would return it to functionality. With the circuit evidently broken, the motor will not respond to the on/off switch.

OK, the part that broke appears to be a "trim pot" (short for "trimmer potentiometer" -- a small board mounted device for fine tuning a voltage in a circuit). Trim pots typically have a total adjustment range of about 3/4 turn or less. The usual procedure for adjusting a trim pot is to make very small adjustments of just a few degrees at a time while some other parameter is being observed for a particular response, such as the voltage at a particular test point on the board or an output response. Also, the proper tool for tweaking a trim pot is a very small all-plastic screwdriver and not a regular metal one. Trim pots are delicate and if treated as if they are a screw will not survive when turned beyond their range of adjustment. From your description, it appears that the trim pot may have been tweaked with a bit too much exuberance. Trim pots are low cost parts and the only things that you would need to know are its form factor and resistance value which would be marked somewhere on the part and possibly on the PWB as well. Typical values would be 5K and 10K. Get somebody else to replace the part as this is not a DIY job -- it is too easy to ruin a PWB.

It is at least a good sign that the motor was working before the trim pot was trashed. That implies that things may still be repairable. I'll take a guess at what "spit and sputter then roar" means. Would it be something like initial sluggish response and perhaps hesitating before starting to respond, but once the motor accelerated up to speed it became very noisy (roaring sound)? That could be caused by worn out bearings in the motor. How long has the motor been exhibiting that sort of behavior?

It appears that motor and drive units are repairable for a price. Since you will need to pay to have things repaired, it is up to you to decide how much you are willing to spend.

 

[JOHN KARTCHNER]

Thanks, Bill. In my feline metaphor roar means to run very fast. No bad bearings. Your expertise is much appreciated. I accept your wisdom and guidance. Since the geeks aren't laboring on Labor Day, I'll start the search tomorrow.
John

 

[Steve Harder]

I'd guess a dirty potentiometer - motor speed jumping around is kind of like the static that you'd hear on an AM radio with a dirty pot (assuming you are of an age to have listened to rock/roll on AM in your youth).

And the pot should be a component that can be replaced relatively easily by any electronics shop that works on circuit boards.