Hi all

I have a small portable power drill that I dipped in the water today briefly and it stopped working as the pcb got wet. Looks like it's destroyed a power transistor of some sort and I will just attempt to repair it.

Could anyone help me identify this component in the picture attached?

Thanks
Donie

 

Could anyone help me identify this component in the picture attached?

Not likely. That package isn't unique to any particular transistor.

You can try searching for the package markings, but with that much damage, it's unlikely that you'll get the complete designator.

You could try creating a schematic from the board and we could make some educated guesses.

 

Thanks dl324. I'm guessing its the same as the identical looking component to it's right but is the designation on the bottom of the component? I wonder is it worth just replacing this component or is it likely that more damage has been done? I'll remove it and see if I can see anything on the other side.

 

I'm guessing its the same as the identical looking component to it's right but is the designation on the bottom of the component?

To avoid guessing, you can trace enough of the circuitry to include the connections to those two transistors.

I wonder is it worth just replacing this component or is it likely that more damage has been done?

How can you replace it if you don't know what it is?

I'll remove it and see if I can see anything on the other side.

Markings for most devices will be on the top of the package.

 

Can you remove whatever the glob of goop on the top of the body is? Such components are usually marked.

It is fairly unlikely that part would be damaged by water. Clean fresh water isn't a big killer of electronics. Are you sure the board is completely dry? If you have clean dry oil-free compressed air available, give it a gentle blast. Water easily gets pulled under surface mount components by surface tension and then stays there the same way. It can take a very long time to evaporate naturally and can cause misoperation without actual permanent damage.

I can't see the whole board, so it may be inadvisable, but if it had been exposed to anything but clean water I would probably blow it off with compressed air, rinse it with distilled water (de-ionized or reverse-osmosis processed OK), blow it off again then have at it with a hair dryer for several minutes.

 

Here is the good and bad component. I think they are identical but haven't found anything yet with F4758.

 

It is made by ON Semiconductor and almost certainly a power MOSFET, but I can't see the markings in the photos. It may be "house numbered" with the board or drill manufacturer's own part number.

It there actually a chunk of the black epoxy missing? There is definitely a solder ball that shouldn't be there in the lower right. They are sometimes left by the assembly process, but I doubt it that is the source here.

 

I can see F 47 58 (20NG)?

 

Got a response from ON semi but it wasn’t helpful. I’d appreciate if anyone has any ideas.

Thank you for contacting ON Semiconductor.

I am sorry but I was not able to identify the device in the attachment. It is possible that it was discontinued a long time ago or that it was a customized device for Bosch.

If you have any further questions, please do not hesitate to contact us back.

 

There is a reasonable chance that any of a fairly large number of N-channel power MOSFETs would make suitable replacements.
My inclination would be to select one that is rated for voltage about 50% or more higher than the battery voltage, "logic level" gate voltage and some very low ON resistance. The FDD6688 from ON might be suitable, but there is considerable guesswork here. There are other similar and possibly better parts from other manufacturers.

One question is what the other FET is for. If the drill has fast braking, that is one possibility, but it might be doing something else. There is an awful lot of circuitry on that board.

 

Thanks ebp, yes, the amount of circuitry surprises me too. It did appear to have instant braking but I’m not sure how that worked. I might do as you say and put in a midget that should work.

I just wanted to look at specs for original part of possible in case there is something special.

I’ll let you know how i get on but if anyone has any experience of this type of drill I’d like to hear what you think.

D

 

Electronic braking is accomplished by creating a negative resistance circuit. To brake a motor, you reverse the direction of the current through the motor. The negative current is made proportional to the back emf of the motor.