Repairing a Milwaukee Sawzall Reciprocating Saw (M18 FSX)

In this video repair a Milwaukee M18 FSX Sawzall Reciprocating Saw. The LED light lights up when the battery is inserted and the trigger is pressed but nothing else happens.

[@SuperMurrayb]

Thanks for posting the interesting and informative videol With the Milwaukee M18 battery the cell pack connects directly to pins 1 and 5 of the connector. The battery pack has no way to prevent discharge so that is left up to the tool. When the battery microcontroller detects that the pack is operating outside of the allowable temperature range or that a cell has fallen below the minimum voltage threshold the battery sends a message to the microcontroller in the tool. The tool then switches off an internal MOSFET to disconnect the battery until the tool receives a power good signal from the battery. That may be why you found a seperate disconnect board inside the tool.

[@BuyitFixit]

Thanks for that. I did work that out in later devices such as the Milwaukee vacuum etc I looked at, but thanks for your comment. I've looked at a lot more Milwaukee devices and even some batteries. The m12 only have a temperature sensor and no protection at all. The m18 batteries only have over voltage protection and as you said the under voltage protection is handled in the tools. I think it was one of the Milwaukee lights I looked at had a fault where the microcontroller was reading the voltage wrongly due to a resistor on the voltage divider being blown.

[@SuperMurrayb]

@@BuyitFixit The m12 tools will stop operating when the pack voltage drops to a certain level but only three pins are used by the tool so it does not appear to have any way to measure individual cell voltages. The M12 charger does use all five pins so I expect it can balance charge each cell in the pack. In the case of the M18 system the "charger" is not a charger. The charge controller is inside the battery and the "charger" provides power to the actual charger inside the battery. It does appear that the M18 charge controller can measure each cell's voltage individually and balance charge each cell in the pack. Having the charge controller inside the battery pack allows them to balance charge five cells using only a five pin connector. Since pins 1 and 5 of an M18 battery connect directly to the pack through a fusable link the battery has no way to directly reduce the output. It can only do it indirectly by communicating with the tool using pins 2 and 4. There does not seem to be any technical details about the protocol they are using except for some marketing nonsense so I can't add any other details.

[@BuyitFixit]

@@SuperMurrayb I did do a bit reverse engineering on the m18 battery pcb. I know there was an i2c fuel gauge type chip on there BQ something or other from memory.. and I'm fairly sure there was a mosfet connected to the output. There were quite a few smaller transistors connected to the individual cells which I guess are for balancing or monitoring. I should perhaps try to reverse engineer the communication protocol as it doesn't appear anyone else has 😂😂

[@SuperMurrayb]

@@BuyitFixit I expect there are many Milwaukee owners that are interested in knowing details about how the tools work. As far as I know there are microcontrollers inside every charger/power supply, every tool, and every M18 battery. It does not look like the M12 battery has any LSI chips in it. Good luck with your research.

[@599miata]

Great job again👍👍

[@BuyitFixit]

Thanks 🙂👍

[@10OZDuster]

so a tiny 5cent resistor failed rendering the whole unit USELESS.....does this meandMILWAUKEES ARE JUNK ???

[@BuyitFixit]

No, it's often one component that renders a whole device useless. That could be anything from a Solid state disk drive (which was one capacitor, on the video I did not too long ago) or something like a PS5 or XBOX, or iPhone.

[@Landesign58]

Great video!!!

[@BuyitFixit]

Thanks 👍

[@brandon7823]

I have the 2722-20 SN# J66A however its not the FSX but same electronics assembly with same issue. Install battery and only light on tell it times out. Then TIME DELAY to get the 20v back at the 20ohm resistor by the power lead in to the PDB. Nothing burnt or chooched that i can find with my AM scope. I tested the 2 resistors in your video both test good. Board chases test good PTP, Trigger tested good along with the potentiometer. I noticed the 12v from the R- as stated in the video drops off on trigger pull then time delay to get the 20v back to the PDB. My 🤔 is the optoic possibly bad or maybe the SE555 timer? I get proper power in threw to all components until (TP) then power drops off to 2v +/- 1v% varying. Tests done with a Fluke 287 DMM. This thing has me stumped🧐. Any help is greatly appreciated. Great video by the way🤓

[@BuyitFixit]

Thanks! It's been a while but the 555 seems to output a square wave when the trigger is pulled it it goes to the top left of the board where there are two small smt transistors. I think it then goes towards the two large mosfets. If you have a scope I'd check that you are getting that.

[@brandon7823]

@@BuyitFixitI forgot to add the mosfets all test out properly.But on a good note called Milwaukee and this PIG is still under warranty so i'm definitely going to try to get a replacement or replaced electronics assembly. Worst they can do is say i tampered with it and its not covered🤷.But again if it didn't fail there would be no reason to be in there to try to fix it so i'm going to go with that. Fingers crossed, I will update ya. Thanks again for the fast response and normally i wouldn't give up because no one learns from it but warranty is free and i can move to the next project. 👌

[@BuyitFixit]

No problem. If you don't get sorted give me a shout and we'll see if we can figure it out!

[@brandon7823]

@@BuyitFixit Absolutely

[@dacar4592]

Hi, is it possible to bypass that board and run the power direct? Will the tool work?

[@BuyitFixit]

I'm not too sure, it's something I've not tried.

[@Carpenterfsweden]

It looks like new and already broken like mine. its a shame for the price

[@BuyitFixit]

Luckily this one didn't cost me full price and was a cheap repair. Hopefully yours is still under warranty.

[@noahlong2158]

Maybe the led is swap able

[@nasdsrekk3503]

Did you find a schematic somewhere for this? As far as what powers what in what order?

[@BuyitFixit]

No I just worked it out at the time. I cant remember the order but the microcontroller needs power before the saw will do anything at all.

[@LilasTools]

👍👍

[@BuyitFixit]

Thanks 👍🙂

[@L_klop]

Hi there, whats the part number for the Foot assemly? I lost mine and not sure is the "Super Sawzal" and the normal "Sawzal" has the same foot. From a quick google it looks like it might be [ 45-16-0030 ] ? Thanks in advance!

[@L_klop]

or Milwaukee 45-16-0135 Shoe Assembly...🤔🥴

[@BuyitFixit]

Really sorry, I'm not too sure on that one.

[@jeremiefaucher-goulet3365]

There's only sound on the left channel. And sadly my right speaker is the only one that works. It was complete silence to me.

[@BuyitFixit]

Sorry about that. I've just tried it on my PC and tried adjusting the balance, and it plays out of both speakers, however I just tried it on my TV with the built in speakers and you are correct. I guess I must have uploaded it as a stereo audio track instead of mono. Thank you for bringing it to my attention.

[@jeremiefaucher-goulet3365]

@@BuyitFixit After writing that comment and a quick Google search, I was able to figure out how to configure Windows in "Mono audio" which combines both channels, so I could watch it properly. So all is good. If all you can produce is Mono, then sure it would be nice to always duplicate on both channels. But otherwise stereo is nice and I encourage you to keep doing stereo.

[@BuyitFixit]

It was about 6 months ago and I was just new to video editing. I now have a template I use and checked my latest videos which all seem to play on both channels. I think I must have had a setting wrong when I did that one. I hope you found the video useful.

[@peanutbutterisfu]

Just fixed mine! The front led was blinking in intervals of 3’s when pulling the trigger. When I took it apart there was a very small black ground wire that was broken, fixed that and good as new.

[@BuyitFixit]

Brilliant! Well done 👍

[@raymihurtadostuart7052]

What’s yours a M18 CSX? Mine has just started with the 3 blinks on the LED. Purchased in 2018. Based in NZ The main frustration is that there’s no info from Milwaukee on these malfunction codes (3 Blinks equals ?)

[@MCH4RSK1HCPAALLIKKO]

@@raymihurtadostuart7052 3 Blinks should be the heatsensor, which is kind of common issue with these.

[@thetraindriver01]

Great fix, a sneaky little resistor hanging around the wires was the culprit 😊

[@BuyitFixit]

Yes, bloody sneaky little things 😂😂😂

[@MrTorch8]

I had some success. 20ohm resistor under the mosfet. Thanks again for your video.

[@BuyitFixit]

Glad it helped!

[@DonaldDavidson-i1b]

Id blades broke . And bent blade in it that wont come out .how u take that shaft apart

[@BuyitFixit]

I'm not 100% I think there was a pin or circlip possibly.

[@HowlingOwls]

Have a milwaukee m18 sawzall that i bought broken. The sawblade clamp was stuck but some oil got i t loose, easy peasy 😁. The other problem is when i put on the battery the saw works good but leting it sit for a few min it wont run. Any idea on where to start looking? Nice channel 😉

[@BuyitFixit]

Thanks. Is it brushed or brushless?

[@HowlingOwls]

@@BuyitFixit Brushless

[@BuyitFixit]

Does the light illuminate when you press the switch when this happens? Or if you move the motor manually by pressing the saw blade part in then trying again does it fire up? It could be anything really..

[@HowlingOwls]

@@BuyitFixit Yes, it does. No pulling or pushing will start it but removing/insert battery makes it run again. I was wondering if there are som timing stuff going on and it freazes then to be reseted by removing/iserting battery. The batteryholder is wobbly but i tried shiming the contacts and strapping the battery to no avail...😑 Guess I have to by a electronics kit for it. Its at least haf the price of a new one here in sweden.

[@BuyitFixit]

Really hard to diagnose without seeing it. Wondering if it could be something with the brake circuit like the one I looked if it fires up after removing and reinstalling the battery. Sounds like the microcontroller is running as the light is controlled by it and it must have power also.

[@swp466]

Great find on the blown resistor! I love finding bargains like these. Did you ever notice that you reinstalled the side hook backwards?

[@BuyitFixit]

Thanks 👍no? I'm not sure it can be put in backwards?

[@swp466]

@@BuyitFixit Yep -- go back and watch the start of the video before the teardown. The hook folds down the side, not over the top.

[@BuyitFixit]

@swp466 oh yes, you're right! I never noticed. I think I've only used it a couple of times since I repaired it so I'll have to swap it over. You're very observant 👍and thanks again for letting me know 🙂👍

[@swp466]

@@BuyitFixit No worries. I just found the easiest M18 Sawzall fix of them all. Brand new one (probably had less than 15 minutes use on it), bought for about 35% of new cost - mechanism seized. When I pulled off the rubber boot, found the factory didn't use Loctite on the crankshaft bolt, or torque it down and it backed out, forcing itself against the crankshaft bearing retainer/cover. Put a dab of Loctite and torqued it in, and it's (literally) good as new.

[@BuyitFixit]

@swp466 Nice one 👍

[@MrTorch8]

I've been doing similar repairs to a number of milwaukee tools. Funnily enough I have an fsx sawzall with what appears to be the same fault. Hopefully it's the same thing.

[@BuyitFixit]

If you get stuck, give me a shout.