Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old December 28th 15, 10:17 PM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

I have a Milwaukee 12v cordless jig saw. It was working fine then
stopped, dead. Then started again, with no symptoms. It did this back
& forth a few times, then stayed dead. It never stopped while being
used - it just wouldn't start at all.

I took it apart to diagnose & as soon as I put it on the battery, it was
OK! I reassembled it and periodically tested it over a week. Always
OK. Today I put the base/shoe back on & it was dead!

As I took it apart again, I kept checking it, but it didn't come back.
And then, sitting there, it did come back, spontaneously.

It has a small PCB for speed control. The PCB also controls an LED
"work light", which comes on when the battery is connected. Except when
it's dead - making the LED a good go, no-go indicator. And showing that
the problem is more basic than speed-control circuitry.

The PCB has a number of wires soldered in through holes. I have checked
all of them. I have stressed the board with mild twisting; I've cleaned
it with carbon tet; and have warmed it with a hair dryer. Nothing had
any effect.

The board is SMT (with a 48 pin chip!), except for the wires, 1 cap, and
the output FETs, which are TH.

Is there anything else that I can try?

Thanks,
Bob






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Old December 29th 15, 12:13 AM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

Bob Engelhardt wrote:
I have a Milwaukee 12v cordless jig saw. It was working fine then
stopped, dead. Then started again, with no symptoms. It did this
back & forth a few times, then stayed dead. It never stopped while
being used - it just wouldn't start at all.


One bad winding on the motor, a bad spot on the commutator, really
worn brushes? (Assuming it's not brushless.)

To check: Get it to the dead state again. With your fingers off of
the trigger, use a stick of wood or something that's not your fingers to
turn the blade a few degrees. Then try the trigger again. If you can
reliably make it start that way, look at the brushes and commutator.

Matt Roberds

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Old December 29th 15, 12:30 AM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

On 12/28/2015 7:13 PM, wrote:
One bad winding on the motor, a bad spot on the commutator, really
worn brushes? (Assuming it's not brushless.)
...


When it's dead, even the LED does not come on. Which it normally does
even without the trigger being pulled. So it can't be commutator, etc.

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Old December 29th 15, 01:22 AM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

On 12/28/2015 6:30 PM, Bob Engelhardt wrote:
On 12/28/2015 7:13 PM, wrote:
One bad winding on the motor, a bad spot on the commutator, really
worn brushes? (Assuming it's not brushless.)
...


When it's dead, even the LED does not come on. Which it normally does
even without the trigger being pulled. So it can't be commutator, etc.


Intermittent battery connection.

Mikek
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Old December 29th 15, 12:46 PM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

On Monday, December 28, 2015 at 10:49:03 PM UTC-5, Bob Engelhardt wrote:
On 12/28/2015 10:13 PM, Bob Engelhardt wrote:
On 12/28/2015 8:22 PM, amdx wrote:
On 12/28/2015 6:30 PM, Bob Engelhardt wrote:
On 12/28/2015 7:13 PM, wrote:
One bad winding on the motor, a bad spot on the commutator, really
worn brushes? (Assuming it's not brushless.)
...

When it's dead, even the LED does not come on. Which it normally does
even without the trigger being pulled. So it can't be commutator, etc.


Intermittent battery connection.

Mikek


I want to say that I've checked that - that there is voltage on the
connector terminals when it was dead. But I've gone around in so many
circles that I can't remember if I was even able to do that. I.e., if
it was ever dead after I opened it.

I have wiggled and stressed the battery connector without consequence.

When it dies again, that will the first thing I check.

Thanks,
Bob


Update: I put it together & it died. It took it apart & it stayed dead.
There is voltage on the connector and on the board. No poking,
prodding, twisting brings it back.

That pretty much clinches it for me: the board is bad. It is curious
how intermittent it was without reacting to anything I did.

The saw is under warranty - if I can find the receipt for it (unlikely)!

Bob


If you can't find the receipt, reflow the board (including the chip). I've seen a lot of reflow repairs where flexing or thermal cycling is inconclusive. Make sure you don't miss the crystal/resonator. Thoroughly clean the board afterwards as some unseen residues can wreak havoc with processor ICs..

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Old December 29th 15, 08:16 PM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

On 12/29/2015 2:52 AM, Charlie+ wrote:
On Mon, 28 Dec 2015 22:48:42 -0500, Bob Engelhardt
wrote as underneath :

snip

The saw is under warranty - if I can find the receipt for it (unlikely)!

You might have baught it with a credit card, the account would give you
proof of purchase.. C+


Oh ... good idea! I almost certainly did use a card. Thanks

Bob
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Old December 29th 15, 08:19 PM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

On 12/29/2015 7:46 AM, John-Del wrote:

If you can't find the receipt, reflow the board (including the chip). I've seen a lot of reflow repairs where flexing or thermal cycling is inconclusive. Make sure you don't miss the crystal/resonator. Thoroughly clean the board afterwards as some unseen residues can wreak havoc with processor ICs.


Thanks. I'll definitely try that if I can't get it fixed under warranty.

Bob
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Old January 1st 16, 05:17 PM posted to sci.electronics.repair
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Default Baffled by cordless tool problem

On Monday, December 28, 2015 at 4:17:44 PM UTC-6, Bob Engelhardt wrote:
I have a Milwaukee 12v cordless jig saw. It was working fine then
stopped, dead. Then started again, with no symptoms. It did this back
& forth a few times, then stayed dead. It never stopped while being
used - it just wouldn't start at all.

I took it apart to diagnose & as soon as I put it on the battery, it was
OK! I reassembled it and periodically tested it over a week. Always
OK. Today I put the base/shoe back on & it was dead!

As I took it apart again, I kept checking it, but it didn't come back.
And then, sitting there, it did come back, spontaneously.

It has a small PCB for speed control. The PCB also controls an LED
"work light", which comes on when the battery is connected. Except when
it's dead - making the LED a good go, no-go indicator. And showing that
the problem is more basic than speed-control circuitry.

The PCB has a number of wires soldered in through holes. I have checked
all of them. I have stressed the board with mild twisting; I've cleaned
it with carbon tet; and have warmed it with a hair dryer. Nothing had
any effect.

The board is SMT (with a 48 pin chip!), except for the wires, 1 cap, and
the output FETs, which are TH.

Is there anything else that I can try?

Thanks,
Bob


Might this be a battery issue? You see, a lot of these modern battery packs have a Battery Management System circuit board inside the battery pack, and its job is to properly charge the batteries and shut off the battery when it's drained. If the battery pack and the saw have to communicate with each other, maybe the BMS says it's time to shut off the battery, yet the battery is not yet dead.

You might be able to check by swapping in a different battery pack.

Good luck and Happy New Year.


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