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Old 09-17-2021, 12:07 PM   #21
eccerr0r
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Default Re: Catapillar ECU repair, need N548AB replacement?

are source or drain grounded? Drain or source connected out to the pins?
Found which pin is ground? battery 24V? 12V?
Those three pin axial devices are capacitors? What voltage/capacitance?
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Old 09-17-2021, 06:44 PM   #22
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Default Re: Catapillar ECU repair, need N548AB replacement?

The 3 pin caps measure about 1400uF on my tester. There are no ratings printed on these caps. It also seems these 3 legged caps aren’t connected to these TO247 devices. 2 of the pins of the TO247 go to the connector while the 3rd pin is just floating. Which doesn’t make any sense. It looks like it goes to a pad and a through hole that doesn’t come out on the other side. I’ve actually made a copper brush to my DMM to find a pad where it comes out but can’t find anything on either side of the board. While pin 2 and 3 of the two TO247 devices are in parallel, pin 1 is separate which I believe is the gate pin. Sine it isn’t connected anywhere it must be floating. Even my dog thinks I ate her kibbles. I’ve made a pic from the other side of the board. That’s where I left for tonight. Maybe I’ll have another go at it tomorrow…
I know the ECU is from a Catapillar MXS maybe a C15
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Old 09-17-2021, 07:27 PM   #23
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Default Re: Catapillar ECU repair, need N548AB replacement?

%#*[email protected] those multilayer boards...
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Old 09-17-2021, 07:51 PM   #24
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Default Re: Catapillar ECU repair, need N548AB replacement?

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Nope. No fuel, as there isnít any HV produced. There is no short to the gate on both, so the gate driving circuit is fine.
Hopefully not the case here if both are measuring the same, but I've seen MOSFETs that blew hard enough that they went open circuit after the event, while acting as a fuse for the now dead-shorted gate drive.
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Old 09-17-2021, 08:54 PM   #25
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Default Re: Catapillar ECU repair, need N548AB replacement?

Other end of the wire should still be continuous with some pad somewhere...at least one would hope they would design the tracks to not fuse before silicon or die bond...
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Old 09-18-2021, 06:29 AM   #26
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Default Re: Catapillar ECU repair, need N548AB replacement?

My question is how would it work if the gate was left floating on the fets I do quite understand how this would work

This is why I do not like devices that have stacked multiple trace boards on each other because it very difficult to trace out not completely impossible but almost impossible to do

Is ECU that expensive that you have to repair it or is for a learning experience which in both cases I completely understand because I have done both
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These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

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Old 09-18-2021, 07:08 AM   #27
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Default Re: Catapillar ECU repair, need N548AB replacement?

would be evil if caterpillar OEMed dummy parts that just short S-D and just used those as jumpers...
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Old 09-18-2021, 07:51 AM   #28
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Default Re: Catapillar ECU repair, need N548AB replacement?

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would be evil if caterpillar OEMed dummy parts that just short S-D and just used those as jumpers...
I would have to totally agree with you on this point
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Old 09-18-2021, 08:46 AM   #29
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Default Re: Catapillar ECU repair, need N548AB replacement?

easy to find out - decap one using nitromores paint stripper or some other resin desolving substance.
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Old 09-18-2021, 08:59 AM   #30
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Default Re: Catapillar ECU repair, need N548AB replacement?

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So this is BS, catapillar trucks have a lifetime of 10 or years max because the battery is not a FRU - and one must get a new ECU every 10 years?
actually some of us have experience with those specific batteries.
they will last about 20years.
then all fucking hell with break loose - literally!
https://www.youtube.com/watch?v=OT9CWbK-2HU
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Old 09-18-2021, 10:12 AM   #31
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Default Re: Catapillar ECU repair, need N548AB replacement?

Depends on how much the battery is used... and how much it's not connected to external power. Those Tadiran batteries have been around for a while and probably has really low self discharge but I've come across many expended Tadiran cells in old computers...
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Old 09-18-2021, 12:30 PM   #32
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Default Re: Catapillar ECU repair, need N548AB replacement?

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actually some of us have experience with those specific batteries.
they will last about 20years.
then all fucking hell with break loose - literally!
https://www.youtube.com/watch?v=OT9CWbK-2HU
This was a mess that he had on his hands he is good at repairing this device
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Old 09-18-2021, 02:03 PM   #33
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Default Re: Catapillar ECU repair, need N548AB replacement?

Well, I don't think I am going to decap that. Why I am doing this? Because no one else can do that around here, money is always an issue, but for me it's just because it's interesting on how this is supposed to work. I've been very busy fixing a lot of stuff, but because of time constraints for the last little while I just post now the harder, interesting stuff. Brain stimulation can't hurt.

So far I haven't found what is driving the gate of the Mosfet. I can follow it to a through hole and then it disappears in the middle layer of the board. I made a makeshift copper brush and went a few times over both sides and got diddly squat. Matter effect unpopulated pads of Q16 and Q26 behave the exact same way then Q2 and Q19. The drain and source are all paralleled (and are connected to Q2 and Q19 as well). The gate pins do the same trick, go to a through hole and disappear in the middle layer of the board. I tried this morning to see what happens if I go hook up a cable tracer to these gate pads and sniff around with a inductive probe. Played around for 5 mins and my 9V battery died. Pfft... Now I need some batteries.
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Old 09-18-2021, 02:24 PM   #34
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Default Re: Catapillar ECU repair, need N548AB replacement?

Well I gave you one possible explanation which is not completely far fetched albeit evil explanation of what's going on. Yes I hate buried vias/buried pads and I think they're also frowned upon for best practices, but can't discount this possibility when you don't know where the s/d pins go?
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Old 09-18-2021, 04:50 PM   #35
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Default Re: Catapillar ECU repair, need N548AB replacement?

I know that what I am going to say sounds nuts, but is it possible to use a MOSFET as a reverse fuse? Good = open circuit, Bad = short? Maybe a over voltage condition occurred due to jumping the truck for example? But why use 2 Mosfets? Baah… this doesn’t make sense in my head! The drain and source pins do go to the main board.
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Old 09-18-2021, 05:09 PM   #36
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Default Re: Catapillar ECU repair, need N548AB replacement?

One possibly is that it goes to the micro controller board instead where you think it should go this is just an idea or somewhere else who knows where that could be another idea as well
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Old 09-18-2021, 06:46 PM   #37
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Default Re: Catapillar ECU repair, need N548AB replacement?

Here is the latest tracing of the board. Sure thing the gates of the TO247ís are floating. It looks like if these conducting between drain and source, the drain pin (red) will send a voltage to the main board, goes through a little 130k resistor, a couple small SMD caps to gnd and goes to the back side of the board. Kinda like a sensing circuit.
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Old 09-18-2021, 06:51 PM   #38
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Default Re: Catapillar ECU repair, need N548AB replacement?

i might get in touch with these people . https://fairchildproducts.com/contact-us-information/
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Old 09-18-2021, 07:21 PM   #39
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Default Re: Catapillar ECU repair, need N548AB replacement?

The way the circuit is hooked up, a fake transistor is not unreasonable... A diode is also possible. A mosfet being used for its body diode only is possible too but a floating gate is bad.

It's also quite possible Fairchild is under NDA to not need to disclose the contents of those chips, worth a shot but don't be surprised if you get shot down...
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Old 09-19-2021, 04:27 AM   #40
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Default Re: Catapillar ECU repair, need N548AB replacement?

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i might get in touch with these people . https://fairchildproducts.com/contact-us-information/
Already did and got nothing back.

Added latest drawings
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