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#1 Marcus M. Jones

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Posted 10 November 2012 - 07:21 PM

a buddy fried one of my rotery tools about a year and half ago. tonight i finally took it apart to see if it could be repaird and this is what i found.
im no electronics expert but i do believe this is a compacitor so any one have a clue on the id of this compacitor?

Posted Image

Thanks in advanced

#2 blunc

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Posted 10 November 2012 - 07:34 PM

Looks more like a wire-wound resistor, most of the time the values are printed on these.

#3 Marcus M. Jones

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Posted 10 November 2012 - 07:48 PM

Looks more like a wire-wound resistor, most of the time the values are printed on these.


nothing is printed on it. if there was it burned off. it does say r3 on the board i don't know if that means anything or not.

#4 Kaleb

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Posted 10 November 2012 - 07:54 PM

It does look like a resistor and your right there is no code. It's usually color coded rings. R3 is the location.

If I'm not mistaken you can ohm a resistor to find its value then replace it with the equivilant. It's been awhile since I have had to manually check one. Most current ones are coded.

Before you determine it's a definite resistor, what is it connected to?

#5 Marcus M. Jones

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Posted 10 November 2012 - 07:59 PM

It does look like a resistor and your right there is no code. It's usually color coded rings. R3 is the location.

If I'm not mistaken you can ohm a resistor to find its value then replace it with the equivilant. It's been awhile since I have had to manually check one. Most current ones are coded.

Before you determine it's a definite resistor, what is it connected to?


its part of the speed control to a benchtop rotery tool.

#6 blunc

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Posted 10 November 2012 - 08:27 PM

The r3 on the circuit board means it is a resistor.
Contrary to common experience, some precision wire-wound resistors do have their value printed on them, I would post an example but I'm typing this on my phone.

Burned resistors rarely give proper value readings so I wouldn't trust it if you do get a reading.

To reduce the risk of failure or fire you need to find an exact replacement resistor, that one looks like it may be a half or one watt rated wire-wound resistor.

Try searching for photos of your speed controller online, you may find one that shows what resistor goes there.

#7 blunc

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Posted 10 November 2012 - 08:30 PM

Since I can't see any code rings on it, I'm thinking the value was printed.

#8 sak

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Posted 10 November 2012 - 09:05 PM

Will it still work if the circuit board beneath it is burnt?

#9 Greg Wann

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Posted 10 November 2012 - 09:12 PM

I built some vacuum tube stereo equipment a few years ago. It was a lot of fun. Is there a schematic in the box lid? You might do a search for your model number and the word schematic. Adding description words of what you have may yield exactly what you need online. I realize what you have is not a vacuum tube amplifier or preamplifier but you still might get lucky

#10 blunc

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Posted 10 November 2012 - 09:39 PM

Will it still work if the circuit board beneath it is burnt?


Depends on how carbonized the board has gotten, I've had some work and some that literally caught fire due to catastrophic failure.

#11 Deathgoblin

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Posted 11 November 2012 - 06:58 AM

Depends on how carbonized the board has gotten, I've had some work and some that literally caught fire due to catastrophic failure.


It also depends on if the pads and pathways are still attached to the board. If it got too hot, they'll pull off as soon as they're unsoldered. It's hard to tell what the value of that resistor is since it's so damaged. Maybe if you know the exact model of the rotary tool, we can find a schematic that will tell us what it is.

#12 Marcus M. Jones

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Posted 11 November 2012 - 07:43 AM

Will it still work if the circuit board beneath it is burnt?


the only 2 things connected to that resistor is the black thing. all i need to do is run a jumper between the two.

#13 Ace-Garageguy

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Posted 11 November 2012 - 09:06 AM

The black thing does appear to be a capacitor, and the resistor appears to have failed due to an internal short, judging from the swelling and cracking of the encapsulation material and the slight bluing of the windings. This could have been brought about by continued running under heavy load on a low speed setting.

If you can't find a schematic online (good luck), contacting the manufacturer the old fashioned way is about your only hope. Most proper schematics of device boards will have a component list to one side of the board layout, and the components will be labeled as they are on the board. Hence R3 is your target, obviously.

It would probably be wise to replace the cap too while you're at it.

It would also be wise to use heat-sinks to protect the components while you solder the new ones back in. Soldering heat can damage things.

"Wirewound Resistors

Wirewound resistors have very accurate values and possess a higher current-handling capability than carbon resistors. Several materials are used to make wirewound resistors. Nickel-chromium is the most common. Copper-nickel, and gold-platinum are also used. They have a resistance range from 0.01 ohm to 178 K ohm. One disadvantage is that it takes a large amount of wire to manufacture a resistor of high ohmic value.

Wirewound resistors do not use a color code. The value is usually stamped on the resistor case.

TROUBLESHOOTING RESISTOR FAULTS

The most common problems to occur with fixed resistors are a change in resistance or a complete failure. A complete failure occurs when the resistor overheats and burns out. When the resistor interior is burned out, it produces an open circuit.

Burned out resistors are often caused by the failure of some other component in a circuit causing an excess of current. A cold solder joint can also cause an open circuit.

The internal composition of resistors make an internal short-circuit nearly impossible. However short circuits can occur on printed circuit boards or at the connections of resistors."


Note the word "nearly" preceeding impossible above. As one respondedt already said, trying to check the resistance with an ohmmeter is pointless if the resistor is burned out, or if it's internally shorted. Once you have a design value for the resistor, it could be instructive to check its resistance AFTER it's removed from the circuit, and compare that reading to the design value. If it's the same, a problem may lie elsewhere in the circuit.

Edited by Ace-Garageguy, 11 November 2012 - 09:17 AM.


#14 blunc

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Posted 11 November 2012 - 02:42 PM

The black thing does appear to be a capacitor, and the resistor appears to have failed due to an internal short, judging from the swelling and cracking of the encapsulation material and the slight bluing of the windings. This could have been brought about by continued running under heavy load on a low speed setting.

If you can't find a schematic online (good luck), contacting the manufacturer the old fashioned way is about your only hope. Most proper schematics of device boards will have a component list to one side of the board layout, and the components will be labeled as they are on the board. Hence R3 is your target, obviously.

It would probably be wise to replace the cap too while you're at it.

It would also be wise to use heat-sinks to protect the components while you solder the new ones back in. Soldering heat can damage things.

"Wirewound Resistors

Wirewound resistors have very accurate values and possess a higher current-handling capability than carbon resistors. Several materials are used to make wirewound resistors. Nickel-chromium is the most common. Copper-nickel, and gold-platinum are also used. They have a resistance range from 0.01 ohm to 178 K ohm. One disadvantage is that it takes a large amount of wire to manufacture a resistor of high ohmic value.

Wirewound resistors do not use a color code. The value is usually stamped on the resistor case.

TROUBLESHOOTING RESISTOR FAULTS

The most common problems to occur with fixed resistors are a change in resistance or a complete failure. A complete failure occurs when the resistor overheats and burns out. When the resistor interior is burned out, it produces an open circuit.

Burned out resistors are often caused by the failure of some other component in a circuit causing an excess of current. A cold solder joint can also cause an open circuit.

The internal composition of resistors make an internal short-circuit nearly impossible. However short circuits can occur on printed circuit boards or at the connections of resistors."


Note the word "nearly" preceeding impossible above. As one respondedt already said, trying to check the resistance with an ohmmeter is pointless if the resistor is burned out, or if it's internally shorted. Once you have a design value for the resistor, it could be instructive to check its resistance AFTER it's removed from the circuit, and compare that reading to the design value. If it's the same, a problem may lie elsewhere in the circuit.


Excellent post!

Marcus> I suggest if you can find a used/replacement speed controller board cheap enough to go that route rather than mess with an unknown quantity of failed parts on the board you have, it may be the difference in resurrecting your tool or finishing it off permanently.

#15 Marcus M. Jones

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Posted 11 November 2012 - 03:08 PM

Excellent post!

Marcus> I suggest if you can find a used/replacement speed controller board cheap enough to go that route rather than mess with an unknown quantity of failed parts on the board you have, it may be the difference in resurrecting your tool or finishing it off permanently.


after all the great help from everyone who replied i have decided it is best just to junk it. i hate to as it is the only tool i have with a flex shaft but finding another board that would work with this would be almost impossible. it also gives me a good excuse to head over to Sears for more cool tools to go along with the flex shaft i will be buying to fit my other one.

Thank You All!

#16 935k3

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Posted 11 November 2012 - 05:03 PM

That board is shot. The black thing is most likely a Varistor for overvoltage protection or thermal protection. They usually short to ground to protect the rest of the circuit. Sometimes an undersized(wattage)resistor is used as a fuse in the circuit which is probably the case here. Regardles repair would not be safe or reliable with the condition of that circuit board.

Edited by 935k3, 11 November 2012 - 05:04 PM.


#17 AzTom

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Posted 13 November 2012 - 02:04 AM

If the board is only for speed control, bypass it and make it a full speed rotary tool. You can buy a plug in type speed control used for routers.

Posted Image

#18 Skydime

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Posted 13 November 2012 - 08:05 PM

Drop by Radio Shack with it. Someone there should be able to help get the part you need if you can't or don't wanna bypass it.

Edited by Skydime, 13 November 2012 - 08:06 PM.


#19 Danno

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Posted 14 November 2012 - 12:04 AM

Safer to junk it. No sense flirting with a bigger failure ... fire.


B)

#20 blunc

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Posted 14 November 2012 - 01:49 AM

Drop by Radio Shack with it. Someone there should be able to help get the part you need if you can't or don't wanna bypass it.


You must have some good Radio Shacks where you live, all the Shacks here are useless for real electronic problems.