Help me troubleshoot my stir plate

[CastleHollow]

I've had this

for a couple years, this weekend it quit spinning. Power light comes on, nobody's home. I am not that electronically inclined, so I'm not sure where to start diagnosing a fix: motor, fuses, circuitry, etc.

Here are some pix of the guts:




Is it worth fixing? Can it be cannibalized as a DIY replacememt project? (I hate throwing anything away.) Should I bite the bullet on a new one? About $65 at LHBS, currently on sale at various sites for under $50.

Thanks for any advice!

 

[day_trippr]

It would take about a minute with a multi-meter to figure out what part isn't working. With no electrical skills you're probably best served giving that plate to someone who can diagnose and repair it. Maybe trade that person a sixer for the effort...

Cheers!

 

[FuzzeWuzze]

It would take about a minute with a multi-meter to figure out what part isn't working. With no electrical skills you're probably best served giving that plate to someone who can diagnose and repair it. Maybe trade that person a sixer for the effort...

Cheers!

This, pretty much the only thing we can say from pictures is..yup the Capacitor isnt popped so its not that.

 

[raouliii]

The transformer, board and potentiometer create a simple voltage rectifier/regulator. If you had a multimeter, a check of the voltage output to the motor would shed some light on whether it's the motor or the voltage regulator. Each component on that board can't cost more than a buck to replace. The motor might take a little more searching, even with a part number.

 

[CastleHollow]

The transformer, board and potentiometer create a simple voltage rectifier/regulator. If you had a multimeter, a check of the voltage output to the motor would shed some light on whether it's the motor or the voltage regulator. Each component on that board can't cost more than a buck to replace. The motor might take a little more searching, even with a part number.

Very helpful, thank you. I have 110v going into the transformer, and 5V coming out. There's no juice at the motor or potentiometer, so it seems like a board issue. All of the resistors show current, except for the striped beige one and the one perpendicular to it. Are those replaceable individual parts, or do I need a new board? I have not been able to find schematics for this.

 

[podz]

Take your board out and turn it over to see if any of the circuit paths are burned.

If not, then just desolder those two parts, take them to radio shack and ask for new ones.

Not very difficult at all since that board was hand-made to begin with.

It's always nice to learn some electronic skills and you get a good feeling if you fix it yourself!

 

[day_trippr]

5 volts AC output from the transformer seems low for this application, which you'd think would be providing something like 0-11 VDC to the fan. Unless, of course, the fan is a 5V device, but even then, you'd want to see something like 10VAC on the transformer output.

Anyway, I suspect that active component standing up near the big cap is a 7812 3-pin linear regulator - or possibly a 7805 if the fan is actually rated for 5VDC.

Either way, the four black-with-silver-stripe axial leaded components across the top of the third image are diodes, forming a full-wave bridge rectifier. The output of that bridge is fed to that big capacitor. Measure across the two pins on that cap and tell us what DC reading you get.

Given there's no voltage on the potentiometer that sets the output of the regulator, the odds are the regulator croaked. Not surprising, as there's no provision for thermal dissipation extant, and those 78XX regulators are friggin' toasters if you put more than a volt or so differential on them with a decent current draw.

Finally, fwiw, unless you have one of the few remaining main-line RatShacks near you, good luck even finding a components section...

Cheers!

 

[CastleHollow]

The capacitor is also reading ~5V (analog multimeter.) The regulator is an LM317T. Fortunately, I do have a few Radio Shacks in my area, so I think what I will do is replace both the regulator and that 510 ohm resistor. I might even take the entire device up to the store to see if they have any recommendations on just replacing the whole board with something that might be more efficient or less prone to failure. If it's under $50, I'm ahead of the game.

If neither of those work, I'll spring for a new stir plate and will probably continue to tinker with this. I appreciate the help, thanks all

 

[raouliii]

Don't assume you'll find anyone at radio shack that knows what they are looking at. Does the motor have a label with specs? Have you checked the DC voltage being provided to the motor at full speed (full rotation of potentiometer)?

5v at the input of a LM317 will be lucky to produce 4v at the output.

BTW, the beige, striped component is a resistor. The black, silver striped components are diodes. Minus the diodes, it's probably this circuit.

I'm with daytrippr on this. That transformer output seems awfully low, but without knowing the voltage spec for the motor there's no way to tell.

 

[day_trippr]

I shudder to think what a RadioShack sales drone might recommend.
For anything...other than some batteries.

Anyway...if you could, flip the board over, set your meter for AC, and measure across the two leads from the output side of the transformer. They should each be connected to a different pair of those four diodes in the row.

The ~5V thing is totally suspicious...

Cheers!