Having problems with mini lathe speed control

[chola]

Hi,

Don't know if any one can help (or if I'm in the right forum), but....

My lathe has developed a problem.

Yesterday while turning away happily, the lathe just went to maximum speed with out warning, I turned the speed / power knob off, the lathe kept going. At this point I hit the emergency stop button, when I released this knob the fuse when 'pop' (quite loud - frightened the crap out of my wife!). It just keeps blowing fuses now. I have pulled the electrics out and checked for swarf, not a trace at all, and all the connections are good (screw terminals nice and tight).

The controller is maked with:

SIEG-FC150BJSMD DC Motor Control Board Sieg Famous

The motors still runs fine, just need to get the board working again, any help with this would be much appreaciated.

Thanks.

Colin

[Al_The_Man]

I would assume it is a SCR controlled drive, Probabally an SCR is shorted.
What size motor is it? If you have access to baldor products down under, they sell a range of DC motor controllers that are relatively cheap, if you buy the open chassis style that do not have the enclosure and you can go this route it is much cheaper.
Al.

[chola]

Hi Al The Man,

Thanks for the help.

Excuse my ignorance, what is an SCR controlled drive?

Is is a component that I could remove and take to my local electronics store for a replacement? I know a little about electronics (obviously not SCR's), but am confident ennough to remove and re-fit a part.

Thanks.

Colin

[Al_The_Man]

The controlling devices, wether SCR's or other types, will usually be 3 lead devices, mounted to a heat sink above the main circuit board, the problem is, miniaturization and surface mount technology, has made it harder to service items like this.
If you feel adventurous, you could unsolder the SCR's and check for shorts between the three leads, if the problem is in another area of the board and it is in fact SMT, then it can present a real trouble-shooting problem.
Al.

[chola]

Hi Al,

Thanks for that. I have had a look at the board and can identify most of the components (mostly resistors, doides, capacitors, transistors etc). The only thing I can see mounted to a heat-sink is a large 3 legged transistor.

Is this what I need to check?

Thanks.
Colin

[Al_The_Man]

The main controlling device is going to be mounted to a heat sink, so if that is the only one detectable, then I would test it for short circuit etc, if it has a part number on it you could google it to get the spec's, as long as it is not an inernal 'House' number.
Al.

[phomann]

Hi,

This guy has a repair service if you wantto go that way.

http://www.unclerabid.com/

Cheers,

Peter.

[pastera]

Talk to Jim Rabidwolf (www.unclerabid.com)

He is the expert on these drives and will normally talk you through fixing it yourself. If you send it to him, his rates are very reasonable.

Somewhere to start:
Continuous full speed - shorted MOSFET, both need to be replaced
immediate blown fuse - shorted bridge rectifier


Your issue with a blown fuse is more probably from the shorted MOSFETs - the current surge from turning on at full speed blew the fuse.
If you have some soldering skill the FETs are <$2 each. Don't try to learn soldering on these boards because the delaminate very easily when overheated.
Aaron

[chola]

Hi All,

Thanks for all the help on this...has literally stopped me dead in my tracks - I was halfway through a cut when the thing died!

I've been without my 'toy' now for 2 days and feel like I've lost an arm!

Al The Man - I think I've identified the components you mention as well so will check these out if I get a chance.


Phomann - nice site you have as well - would be nice to connect on e of your controllers up!! - thanks for the link to unclerabid (and from pastera). This guy seems like the go if I have no luck (he is highly recommended on a number of different sites as well).

Pastera -thanks for the quick tips. The way it actually started was half way though a cut, all was progressing nicely then it went to maximum speed and after I shut it off with the emergency stop, then turned back on it blew fuses. This sounds like the problem to your solutions!

I'm not bad with the soldering (and modest too ). Actually it's all in the soldering iron I've found in the past (and a steady hand helps). Luckily I've got a high wattage variable temp unit that gets the heat down fast so no issues there.

Thanks again for all the help.