Name of soic component?

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billmiller

Joined Sep 13, 2013
1
This board is from a harbor freight rechargeable oscillating tool. Advertised oscillating is from 10,000 to 20,000 cycles per second. I need oscillations around 8,000 so I removed the 273( pure experimental here ) resistor and replaced it with a 1k(1/4 watt ) resistor. Oscillations are now adjustable from around 7200 and up. This satisfied my need. I have about two dozen of these I use but one gets hot in hand, quite warm to the touch, and eventually goes to high oscillation. I removed the board and checked resistor(de-soldered) and it was open circuit. I checked diode(1N4007 )(also de-soldered) and it was open circuit. I soldered in new components and results were high oscillation, no adjustment downward. I found data sheet for the mosfet but not the 8 pin IC. I thought maybe some form of 555 timer or op-amp but only guessing. Does anyone know what that chip is? (see picture board3.jpg)
I came up with an idea last night to measure resistance through some of the motors for comparison.
It's always possible I slowed the oscillations below their design criteria!
Oscilloscope shows a nice square wave until motor is soldered in and the wave is very spiky and irregular but still adjustable on all other units.
Bill
 

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Gibson486

Joined Jul 20, 2012
317
Could be anything. Fet driver, a 555 as you mentioned, even a motor IC. I can see why you are thinking 555, but I think it is missing a capacitor to be so. The bad thing is that it is from Harbor freight, so the design is probably cheap. I used to debug designs for mass produced small appliances. Some of the designs were pretty clever for cost savings, but not really ideal when things go wrong. It was kind of horrifying to, but I guess that since it passed all the conformed lab testing, it had to be safe, right?
 
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