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Old 08-10-2021, 08:56 AM   #1
braxton
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Default Black and Decker 40V Lithium weed trimmer PCB board damage

I have a Dewalt / Black and Decker 40V trimmer model LST136 Type-1.

It stopped working. Trimmer motor tests fine. I opened it up to find that the controller board had a blown component at position Q5. It also looks like a similar component at D6 has a bulging area. These two mosfets? are attached to a heat sink. The D6 component looks to be a MBR20100CTP rectifier. The Q5 component blew apart, so its difficult to read the label. I am hoping to get help identifying the Q5 component. Pictures are attached.

In the photos, the heatsink and the Q5 component have already been removed from the board. One of the three legs broke off of the Q5 component.
The last 2 pics are of the component I need help identifying.
Attached Images
File Type: jpg IMG_7911.jpg (672.2 KB, 20 views)
File Type: jpg IMG_7910.jpg (515.1 KB, 26 views)
File Type: jpg IMG_7908.jpg (365.4 KB, 22 views)
File Type: jpg IMG_7909.jpg (728.5 KB, 27 views)
File Type: jpg IMG_7913.jpg (472.3 KB, 23 views)

Last edited by braxton; 08-10-2021 at 09:01 AM.. Reason: corrections and additions
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Old 08-10-2021, 09:11 AM   #2
stj
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

100v is too low for a schottky diode - 250v atleast.
ideally 10x the running voltage!
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Old 08-10-2021, 09:17 AM   #3
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by stj View Post
100v is too low for a schottky diode - 250v atleast.
ideally 10x the running voltage!
Thanks. I will keep that in mind when ordering the D6 component.
Any idea what Q5 is?

I am attaching two more photos of the board
Attached Images
File Type: jpg 2480832F-411E-4A38-AA7C-22E08BA39510.jpg (220.2 KB, 25 views)
File Type: jpg E1CDF579-FA6B-4CBF-A07E-5133FB5BDD82.jpg (218.9 KB, 24 views)

Last edited by braxton; 08-10-2021 at 09:21 AM..
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Old 08-10-2021, 05:03 PM   #4
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Be careful with protection boards when repairing them make sure that the battery are not fully charged if necessary run them down to 3.2 volt and be ready to remove it from the tool or the charger if something goes horrible wrong

I have repair Ryobi battery packs sometimes you can repair them sometimes not
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
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Old 08-12-2021, 06:59 AM   #5
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by braxton View Post
Thanks. I will keep that in mind when ordering the D6 component.
Any idea what Q5 is?

I am attaching two more photos of the board

Try and find someone who owns one (or buy a new one), open it up, identify the part, and then return it?
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Old 08-12-2021, 08:13 AM   #6
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

I just noticed that this battery pack is 40 volts which I do not have

Just be aware of this if this is an older battery pack the controller board of a new one might not be the same as one you have

Last edited by sam_sam_sam; 08-12-2021 at 08:24 AM..
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Old 08-12-2021, 08:51 AM   #7
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Here are photos of the trimmer with the model number.
The board is from inside the handle part.

The board is not from the battery itself.
Attached Images
File Type: jpg 9F44E855-E929-4C30-BD2A-341B0B65F779.jpg (913.3 KB, 10 views)
File Type: jpg EBBA2C33-99F5-477A-915C-34DEEC8D9FBC.jpg (255.3 KB, 11 views)

Last edited by braxton; 08-12-2021 at 08:52 AM.. Reason: Addition
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Old 08-12-2021, 09:46 AM   #8
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Based on a closer look at the blown chip, it looks like it is an Infineon IRL3705Z mosfet.
Digikey lists it as obsolete.

Can anyone help out finding this part or an equivalent?
Thanks.
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Old 08-12-2021, 11:12 AM   #9
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by braxton View Post
Based on a closer look at the blown chip, it looks like it is an Infineon IRL3705Z mosfet.
Digikey lists it as obsolete.

Can anyone help out finding this part or an equivalent?
Thanks.
If that is the correct mosfet...
Digikey IRL3705ZPBF-ND direct replacement, in stock
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Old 08-12-2021, 02:21 PM   #10
braxton
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by R_J View Post
If that is the correct mosfet...
Digikey IRL3705ZPBF-ND direct replacement, in stock
Thanks!
Ordered a few of those and the MBR20200CTP (200V instead of 100V)

Hopefully that will get the trimmer working again...
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Old 08-12-2021, 03:03 PM   #11
R_J
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Check the gate drive circuit resistor (R24) to make sure it is not open, When the mosfet shorted, many times it also takes out the drive ic, that sot23-5, best to get it's number before it is also unreadable.
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Old 08-12-2021, 05:19 PM   #12
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

This means that the charger has the protection board and the battery has no protection board might not even have a protection fuse in it

When you test this board be careful and be ready to disconnect the battery very quickly if something goes horrible wrong
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Old 08-12-2021, 09:35 PM   #13
braxton
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by R_J View Post
Check the gate drive circuit resistor (R24) to make sure it is not open, When the mosfet shorted, many times it also takes out the drive ic, that sot23-5, best to get it's number before it is also unreadable.

R24 resistor has 753 written on it and tests at 75.5 Kohm
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Old 08-12-2021, 09:45 PM   #14
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by R_J View Post
Check the gate drive circuit resistor (R24) to make sure it is not open, When the mosfet shorted, many times it also takes out the drive ic, that sot23-5, best to get it's number before it is also unreadable.
The sot23-5 chip is hard to read but it looks like GX3mD maybe?
Attached Images
File Type: jpg 25A9EA35-CB34-4AFC-A0DB-D559BE8E2257.jpg (247.8 KB, 13 views)
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Old 08-13-2021, 05:32 PM   #15
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Replacing the 2 chips had no effect. Still dead.
What about this component (largest chip in the corner) in the attached photo?
Attached Images
File Type: jpg 51BFC3C0-D819-4A42-A6B2-3BD2323E3856.jpg (366.8 KB, 11 views)

Last edited by braxton; 08-13-2021 at 05:43 PM..
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Old 08-13-2021, 08:15 PM   #16
stj
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

the "dale" part is a resistor - it should look like a short circuit.
clean the board with alcahol - it's hard to see the parts clearly.
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Old 08-13-2021, 09:49 PM   #17
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

After a closer look R24 is likely the resistor between the mosfet source pin (Dale resistor) and the CS pin of the ic, and not the gate drive resistor. Check that the resistors between the gate and the ic are ok.

Last edited by R_J; 08-13-2021 at 10:21 PM..
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Old 08-14-2021, 09:06 AM   #18
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by R_J View Post
After a closer look R24 is likely the resistor between the mosfet source pin (Dale resistor) and the CS pin of the ic, and not the gate drive resistor. Check that the resistors between the gate and the ic are ok.
I tried to take better photos of the board.
I also measured all of the resistors on the board and all seem to give an ohms reading (Highest was 100K and none seem to be open as far as I can tell).
Attached Images
File Type: jpg 5CE430EC-0FE2-474B-BCFC-76DCBAE3EB42.jpg (290.7 KB, 9 views)
File Type: jpg FA05D39C-D4D1-4D22-B334-188826AE59E6.jpg (325.0 KB, 9 views)
File Type: jpg 20271F4D-A091-4551-AD3B-75BA54B090D8.jpg (420.2 KB, 10 views)
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Old 08-14-2021, 10:27 AM   #19
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

what about these solder joints ?
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File Type: png Screenshot from 2021-08-14 17-26-41.png (167.7 KB, 14 views)
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Old 08-14-2021, 02:58 PM   #20
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Default Re: Black and Decker 40V Lithium weed trimmer PCB board damage

Quote:
Originally Posted by petehall347 View Post
what about these solder joints ?
I agree with you that these connections do not look very good
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