Caterpillar ECU repair, need N548AB replacement?

[eccerr0r]

Re: Catapillar ECU repair, need N548AB replacement?

How thick is the metal portion in the "heatsink" portion?

Not familiar with TO247AC construction since it was meant to be isolating, but a TO220 and TO3P the die is bonded straight to the heatsink pad which is really thick compared to the pin... so it can conduct heat away from the die.

What I'm seeing is that the heatsink pad is ... really thin? Thin enough so that it can actually be torn?

Die should be soldered to the heatsink pad, decapsulation usually damages die bonds. Also centered to reduce thermal resistance...

As much damage as it's taken now, is D-S still shorted?

[stj]

Re: Catapillar ECU repair, need N548AB replacement?

but you have no silicon wafer - there is no semiconductor on the heatsink - never was!!

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

thats a fucking fake!!

take a blade and scrape the resin away between the outer pins - it's gonna reveal a bus-bar!!!

problem is the short was between the middle pin and one outer pin! Still scraping away... man... this stuff is hard!

edit: I gave up scraping. However I did put the decapped bottom part with the middle pin under a microscope and it does reveal a little solder blob like substance sticking to the metal. I looked on at the other half top part and sure there is a tiny pinhole in the whatever this plastic is made out of. To me, that is blown Drain Source pins.
You look at my post #60, second picture... you can see it.

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

I'm half asleep but that didn't look much like a transistor. It doesn't seem to have a company logo either??

It looks like a hunk of metal.

I wonder if the device is actually a heatsink to help cool the board?

Look at my first post. It is clearly a fairchild device. It's heat sinked to the casing, not to the board.

CapLeaker

But the question is have we figured out what type of device this is

To me a regular PNP / NPN transistor does not make any sense at all. More plausible is either a diode in disguise or a mosfet of some sort.

Haven't tried this yet, but lets say it is a mosfet. What happens if the gate isn't hooked up. There are actually schematics for other things that do show a mosfet with a floating gate. Most sense as of today in my mind in my particular case is a mosfet with a body diode and use it as a reverse fuse. Basically if something happens it will conduct drain and source pins and throw this way an error. Question here is: WHY are there 2 of them in parallel? At least it's not a dummy device with a jumper built in.

If I put my DMM in Ohms, put my negative probe at the source pin and the positive probe to the positive side of cap C2, I get close to 600k resistance.

[stj]

Re: Catapillar ECU repair, need N548AB replacement?

thats a fucking fake!!

take a blade and scrape the resin away between the outer pins - it's gonna reveal a bus-bar!!!

[sam_sam_sam]

Re: Catapillar ECU repair, need N548AB replacement?

CapLeaker

But the question is have we figured out what type of device this is

[Agent24]

Re: Catapillar ECU repair, need N548AB replacement?

I'm half asleep but that didn't look much like a transistor. It doesn't seem to have a company logo either??

It looks like a hunk of metal.

I wonder if the device is actually a heatsink to help cool the board?

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

should be able to also tell from the silicon a diode from a transistor. Photograph of the "decapsulation" would be nice.

Even if there's just a piece of metal that bridges two pins...

Sorry for the late reply, things got a bit too busy at work. So here is what I did: I took the FET off that cement paste and jammed it in the vice side ways. That took the top off very nicely!

[eccerr0r]

Re: Catapillar ECU repair, need N548AB replacement?

should be able to also tell from the silicon a diode from a transistor. Photograph of the "decapsulation" would be nice.

Even if there's just a piece of metal that bridges two pins...

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

put the part in a vise and bend the tab so the resin cracks away from it - see if it actually has a square of silicon in it.

I'll try that tomorrow.

[stj]

Re: Catapillar ECU repair, need N548AB replacement?

put the part in a vise and bend the tab so the resin cracks away from it - see if it actually has a square of silicon in it.

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

Not sure they would frequently both short out at the same time when in parallel either. And surprised there's not a heat stress mark on the PCB.

I still would not discount it's a dummy device. Not enough clues to point to it being a MOSFET in my books at least.

Is this another case of Topcat's No-Nos, "got board to fix, no way to test" (i.e. you don't have access to the rest of the TV/truck?) Or at least a FSM?

Nope, I don't have the truck. I still have to do some more tracing in order to see if I can find something new.

[eccerr0r]

Re: Catapillar ECU repair, need N548AB replacement?

Not sure they would frequently both short out at the same time when in parallel either. And surprised there's not a heat stress mark on the PCB.

I still would not discount it's a dummy device. Not enough clues to point to it being a MOSFET in my books at least.

Is this another case of Topcat's No-Nos, "got board to fix, no way to test" (i.e. you don't have access to the rest of the TV/truck?) Or at least a FSM?

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

The chances of 2 Mosfets in parallel shorting out are pretty good. Actually that is one reason I don't like that method.

The short on the device measures 0.2 Ohm, same as touching the 2 probes together, like a dead short.

Can't see the inner layer of the board. The outer layers are made that way, I cannot shine a 1000 lumens Olight through it in order to see anything of the middle layer.

The cover has maybe an interesting number printed on it: MXS69947
The truck is a 2007 pre emissions. Some other numbers: BB55U and 248-5546.

Working on the rest to figure out later today.

[eccerr0r]

Re: Catapillar ECU repair, need N548AB replacement?

It's very unlikely both the MOSFET gate and driver both fused at the same time, one will give way first. Also there are two MOSFETs in parallel and what's the chances both failed the same way. I still think there are too many depop devices on the board for that to be a real MOSFET there. Plus two shorted diodes in parallel? What's the chances of that?

How many ohms is it from the "apparent" D to S pins? Dead 0 ohm short or have a few tenths of an ohm?

Still think it's a SHORT dummy device and barking up the wrong tree. Anyway curious of what the part number is for the other devices on the board, are they typical or also caterpillar corrupted?

[redwire]

Re: Catapillar ECU repair, need N548AB replacement?

I would think either the parts are Schottky rectifier diodes with oddball pinout, or the gate-drive pcb trace fused somewhere and is open-circuit? I'll see a little black mark on an inner layer if this happened, using a bright light and magnifier to inspect the board.
Or, a gate-drive resistor got hot and fell off the board once the solder melted.
I keep thinking the gate connects somewhere to something and just have to find it.
Does any lead on the mosfets connect to GND? As a low-side switch. I'd also follow the mosfet pins whichever connects to the ECU 70-pin connector, to find out what solenoids etc. the parts are driving and who the fuse is.

The model number of the ECU would help, sometimes there are schematics out there.

edit: usually a shorted mosfet fuses all three pins together as a blob. So the old parts should have continuity to the gate, unless the bonding wires fused open circuit.

[eccerr0r]

Re: Catapillar ECU repair, need N548AB replacement?

If gate is unconnected, it simply cannot be a MOSFET.

[CapLeaker]

Re: Catapillar ECU repair, need N548AB replacement?

I am still intrigued on how this thing is supposed to work. Let’s say it is a MOSFET with the gate left unconnected (floating). Wouldn’t the MOSFET be turned on if the source and drain have power? Basically working or shorted MOSFET wouldn’t make any difference in this case? More sense it makes if the MOSFET has a body diode, it would be a diode in disguise marked as a transistor rather than a diode.

[eccerr0r]

Re: Catapillar ECU repair, need N548AB replacement?

I sure wouldn't use a jumper as a current amplification device.

[stj]

Re: Catapillar ECU repair, need N548AB replacement?

gotta say, if i was designing an injector driver then those would be darlingtons