My Bosch PSR 14.4V cordless drill doesn't work properly. It always run on full speed, it's not possible to control the speed by adjusting the pressure on the power button. This means it can only be used as drill, not a screw driver. The battery indicator LEDs which normally show the battery level are flashing. It's probably an error code or something.

I have dissambled the drill and found what appears to be a burned MOSFET, see these photos:


The first photo shows the burned component, the other one shows a close up of what appears to be a similar component with the text 95 48 04NG.

My questions:

  1. I believe it is a 04NG MOSFET, but what does the other numbers mean?

  2. Is it likely that the burned component is identical to the one in photo #2?

  3. Should this MOSFET from Ebay be okay?

  4. It it likely that other components are dead too?

  • In many cases the most practical solution with modern methods of electronic construction is "buy a whole new unit" - you might get lucky, and then again you might spend a lot of time and money and not fix it. – Ecnerwal Sep 21 '16 at 16:01
  • I'm voting to close this question as off-topic because it is about identifying an electronic component, speculating whether a manufacturer used it in more than one place on a schematic, and comparing its specifications with another part. – Niall C. Sep 22 '16 at 5:07
  • @NiallC. Then where does it belong? To the electronics site? Hmm, and would about this topic from the help center: "Identifying the source or cause of a problem within your home." ? – marlar Sep 22 '16 at 12:37
  • We asked but they don't want it. – Niall C. Sep 22 '16 at 13:11
  • I am confused about the reply. It says "It has good answers" which I see as a positive thing. Anyway, I got an few answer and accepted one, so that's fine. I just really don't understand this off-topic thing off Stackexchange (but I not alone here). BTW, could it be migrated to electronics? – marlar Sep 22 '16 at 14:38

The good (at least not burned part) MOSFET in your pictures I take it is the 04NG which is an N-channel MOSFET. The added numbers on this parts markings have to do with various information like manufacture, location of manufacture, date or production line numbers.

As far as it being identical, I would suspect that not to be this case. If they both were connected to the same location for the heavy sink buss terminal of that part then more likely they would be, but as seen they are connected to two different locations. If you trace the blue wire and the white wire they likely go to opposite polarities on the battery. This could be one is used forward and one reverse.

The one on EBAY could possibly replace the one that does not look burnt. If the burnt one is the same yes it could work if it is instead the P-Channel version then no it will need the P-Channel version of 04NG. The issue I see is parts sources like Mouser list 04NG as 40V but most are shown as 120amp units. The EBAY unit is listed it as 30amp. I would look for at least a 120A version for replacing.

There is always a chance other parts were damaged, it is a roll of the dice after a tech inspects for obvious parts and replaces those. Before buying and replacing the obvious components check and see if there is a chance to buy the whole board cheaply. If the board is close to the part only price you then can reduce the worry on some of the other parts on the board being bad.

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  • It's not a bad guess that they may be a H-bridge/push pull and so matching p and n channel. – D-on Sep 21 '16 at 15:51
  • It is very hard to tell without a schematic and only can be based on the two heavy primary wires that are running to the board. Also based on the normal value for the part number being 120A, I can not see two being used for current. That and the fact they make a high current version that is near 180 amp of the 04NG. So push pull is a likely conclusion. – spicetraders Sep 21 '16 at 16:31
  • I did not mention but would suggest that the OP unsolder the bad part and test the unit with it out of circuit. If that part is shorted, then once removed will stop the always running. If it is a push pull operation then a chance the unit will run one direction. – spicetraders Sep 21 '16 at 16:35
  • Thanks. Since the burned component probably is different than the good one, I will stop here. Without a schematic, it's too much trial and error. If they were likely to be the same, I would take the chance and order a 04NG. – marlar Sep 22 '16 at 12:39

I believe it is a 04NG MOSFET, but what does the other numbers mean?

4804N - part number for N-channel MOSFET
G - lead (Pb) free

Other markings typically indicate manufacturing location, and year and week of manufacture. E.g. 2009 week 45.

Is it likely that the burned component is identical to the one in photo #2?

There's a chance I guess

Should this MOSFET from Ebay be okay?

Obtain it's datasheet and compare the specs with that for the part made by On Semiconductor

It it likely that other components are dead too?

There's a reasonable chance that whatever killed the MOSFET

  • also killed other stuff
  • will kill the next one

Or you might well get lucky, its a relatively cheap and easy fix to try.

Obviously, you have to solder the underside of the new MOSFET to the large pad on the PCB, this can be tricky. you need to thoroughly clean away the conformal coating, flux residue and excess solder from that area first. You need to apply enough heat to make a good solder connection underneath but not so much heat that you fry the new MOSFET.

Obtaining a new PCB (part 2 609 003 138) may be expensive (~£45)

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