Author Topic: Pendular saw control board problem  (Read 2698 times)

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Offline carcanhol

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Pendular saw control board problem
« on: November 10, 2015, 12:59:40 am »
Hi, a friend gave me this pendular saw and it has a problem in the control board.
The motor is DC.
I used an hp printer transformer at 32V directly at the motor and it ran fine but slow(need more voltage?)
It was too slow to cut wood so i ordered some replacement parts hoping to make it work.
The problem was when you turn it on it runs a bit slow and 5 sec later it goes full throttle but more than it should by factory(400 to 1600RPM).
Now i swapped the components in the pictures and it doesn't run always when pressing the on button and when it runs it goes full throttle again and stops after 2 sec.
Anyone have an idea of what is happening? a friend told me those large ceramic? capacitors break a lot. or it could be the diodes?
thanks for any help.
 

Offline SeanB

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Re: Pendular saw control board problem
« Reply #1 on: November 10, 2015, 03:24:49 am »
Change C4, as it likely has self healed itself down to a low value.
 

Offline bookaboo

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Re: Pendular saw control board problem
« Reply #2 on: November 10, 2015, 04:22:04 am »
Have you tested the electrolytics for ESR and value? May as well just change them while your at it.
 

Offline carcanhol

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Re: Pendular saw control board problem
« Reply #3 on: November 10, 2015, 05:31:07 am »
Change C4, as it likely has self healed itself down to a low value.

No good, motor still rotates 1 turn or so and stops after several tries on the power switch.
Thx ;)
 

Offline carcanhol

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Re: Pendular saw control board problem
« Reply #4 on: November 10, 2015, 05:32:49 am »
Have you tested the electrolytics for ESR and value? May as well just change them while your at it.

A Fluke 79III could be used to test?
Going  to change for some nipons i have.
Thx ;)
 

Offline carcanhol

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Re: Pendular saw control board problem
« Reply #5 on: November 10, 2015, 05:54:25 am »
Changed the electrolytic caps and is the same symptoms.

 

Offline carcanhol

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Re: Pendular saw control board problem
« Reply #6 on: November 10, 2015, 12:40:57 pm »
i have 0.8v on the opamp power pins does that mean some zener is busted a not giving it the voltage needed?
 

Offline Circlotron

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Re: Pendular saw control board problem
« Reply #7 on: November 10, 2015, 01:05:23 pm »
Single sided board that has no plated through holes is liable to have cracked solder joints. Re-solder everything then see what happens.
 

Offline bookaboo

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Re: Pendular saw control board problem
« Reply #8 on: November 10, 2015, 08:25:05 pm »
i have 0.8v on the opamp power pins does that mean some zener is busted a not giving it the voltage needed?

That or something's pulling the line down, or the zeners not getting a supply to start with.
Sketch a schematic out, that usually makes it easy.
 

Offline carcanhol

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Re: Pendular saw control board problem
« Reply #9 on: November 11, 2015, 05:28:00 am »
Single sided board that has no plated through holes is liable to have cracked solder joints. Re-solder everything then see what happens.

Done, no change, i'm going to make a schematic, strip all components test them all resolder the clean board and if this is not going to work i kill this bitch.  >:D
 

Offline carcanhol

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Re: Pendular saw control board problem
« Reply #10 on: November 11, 2015, 05:29:42 am »
i have 0.8v on the opamp power pins does that mean some zener is busted a not giving it the voltage needed?

That or something's pulling the line down, or the zeners not getting a supply to start with.
Sketch a schematic out, that usually makes it easy.

Using the diode test on the MM is good to test zeners?
 

Online blueskull

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Re: Pendular saw control board problem
« Reply #11 on: November 11, 2015, 06:11:26 am »
i have 0.8v on the opamp power pins does that mean some zener is busted a not giving it the voltage needed?

That or something's pulling the line down, or the zeners not getting a supply to start with.
Sketch a schematic out, that usually makes it easy.

Using the diode test on the MM is good to test zeners?

0.8V seems not like a fried zener. They tend to fail short, dead short.
 

Offline bookaboo

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Re: Pendular saw control board problem
« Reply #12 on: November 11, 2015, 06:13:44 am »
i have 0.8v on the opamp power pins does that mean some zener is busted a not giving it the voltage needed?

That or something's pulling the line down, or the zeners not getting a supply to start with.
Sketch a schematic out, that usually makes it easy.

Using the diode test on the MM is good to test zeners?


Depends how high a forward voltage they can put out, if it's lower than the rated zener voltage you wont get a reading. You could try removing the parts on that supply line then testing the voltages at the resistor and zener that way, or remove the zener and use a suitable resistor and power supply to test.

Removing the components on that line one by one may isolate the problem if you voltage at the zener returns to normal.
« Last Edit: November 11, 2015, 06:17:03 am by bookaboo »
 


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