Problem with Mastercarver Micro-Pro

[Owen Lowe]

My baby-blue Micro-Pro carver no longer has speed adjustment - just full tilt in both forward and reverse… Last weekend I was doing a little detail sanding at about 1/2 speed when suddenly the carver ramped up to full speed. Rotating the speed knob had no affect in either forward or reverse.

1) I emailed the company for technical advice but have gotten no answer in the last week.

2) I tested the speed rheostat as best as my limited electrical knowledge allowed by:

• measuring ohms in various combinations between two of the three rheostat leads;
• the outside leads measure a hair over 10 ohms;
• the left lead to center measure changes depending on the rotation of the knob;
• the right lead to center measure changes in complement to the above measurement.

For example, if the knob is moved to some middle-ish position, the L to center might read 4.5 ohms - the R to center will read 5.5. No matter where on the rotation the L to center and R to center add to 10.

Is this what you would expect to see for a properly functioning rheostat?
Has anyone else here had a similar issue with their Micro-Pro?

Thanks for any help you can offer.

 

[Bill Boehme]

Sounds like an electronic component failure. If you're able to make voltage measurements with the device running, see what you get for the voltage to the motor as your chance the potentiometer setting. I would guess that you will see the full-on voltage all the time. It's probably an SCR that has given up its magic smoke. These days nobody does individual component replacement on printed wiring boards so they will probably just swap boards or depending on cost maybe the whole controller box.

 

[Owen Lowe]

Sounds like an electronic component failure. If you're able to make voltage measurements with the device running, see what you get for the voltage to the motor as your chance the potentiometer setting. I would guess that you will see the full-on voltage all the time. It's probably an SCR that has given up its magic smoke. These days nobody does individual component replacement on printed wiring boards so they will probably just swap boards or depending on cost maybe the whole controller box.

Thanks Bill. I revisited the Mastercarver website and noticed they sell motherboards for this carver. In the description is mentions a motherboard problem is no speed control. Cost is $40, so that doesn’t hurt very much — had to locate the medium wallet-crowbar. One is on order and will update here if this solves it.

 

[Owen Lowe]

Update on the no-speed problem:

I received and installed the replacement motherboard — took all of 5 minutes — and the carver is back to working properly. On the board itself it has a version 3 notation while my old one says version 2. Hopefully version 3 replaces whatever weak component(s) has caused the issues for Mastercarver to sell replacement motherboards.

 

[Barry Crowder]

Nice of you to follow up. I've had bad luck with speed controllers, and the replacements were always much more expensive than this. Good to hear that you got yours working again for US$40.