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Old Today, 05:10 AM   #61
Agent24
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Default 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?
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Old Today, 05:11 AM   #62
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Default Re: Catapillar ECU repair, need N548AB replacement?

CapLeaker

But the question is have we figured out what type of device this is
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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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All of these had CAPs POOF
All of the mosfet that are taken out by bad caps
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Old Today, 06:50 AM   #63
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Default 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!!!
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Old Today, 06:51 AM   #64
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Default Re: Catapillar ECU repair, need N548AB replacement?

Quote:
Originally Posted by Agent24 View Post
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.

Quote:
Originally Posted by sam_sam_sam View Post
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.
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Old Today, 06:58 AM   #65
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Default Re: Catapillar ECU repair, need N548AB replacement?

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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.

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Old Today, 09:08 AM   #66
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Default Re: Catapillar ECU repair, need N548AB replacement?

but you have no silicon wafer - there is no semiconductor on the heatsink - never was!!
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Old Today, 10:15 AM   #67
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Default 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?
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Old Today, 10:37 AM   #68
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Default Re: Catapillar ECU repair, need N548AB replacement?

It would be interesting to find out what is this device because things are not adding up to exactly what this device is
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Old Today, 11:48 AM   #69
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Default Re: Catapillar ECU repair, need N548AB replacement?

oh wait, well at least I'm not the only one who hasn't fully awakened yet... of course it's not going to conduct

The photos are convincing to me now, SHorT.
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Old Today, 02:52 PM   #70
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Default Re: Catapillar ECU repair, need N548AB replacement?

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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?
The heat sink part is thick and really heavy compared to the top part. I am talking 1.6 gram vs 4.0 grams.O.k. put it this way: the short was between the middle pin 2 and the last pin 3. Something definitely went sour inside on pin 3 and blew through that plastic and shorted out to the heat sink part on pin 2.

Quote:
Originally Posted by sam_sam_sam View Post
It would be interesting to find out what is this device because things are not adding up to exactly what this device is
No kidding... that's why I put it here. A mystery device and a weird circuit. Couldn't pass that.

Maybe I'll put that top part on my belt sander and see what that does.
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Old Today, 02:55 PM   #71
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Default Re: Catapillar ECU repair, need N548AB replacement?

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but you have no silicon wafer - there is no semiconductor on the heatsink - never was!!
Sadly I have to agree here.
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Old Today, 03:36 PM   #72
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Default Re: Catapillar ECU repair, need N548AB replacement?

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Originally Posted by CapLeaker View Post
Something definitely went sour inside on pin 3 and blew through that plastic and shorted out to the heat sink part on pin 2.
Or as I postulated early on, it was welded that way to begin with!

If it was a diebond that shorted through a die... it sure would not have separated like that, diebonds are physically weak and the die soldered to the metal would hold on, and you will get the die remnants.

So yes, you got SHorT dummy device here and need to look elsewhere for issues, perhaps that other device that connects to these dummies -- is that shorted?
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Old Today, 05:06 PM   #73
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Default Re: Catapillar ECU repair, need N548AB replacement?

Why make such a device for a dummy short. Much cheaper to put a piece of wire in!
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Old Today, 06:05 PM   #74
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Default Re: Catapillar ECU repair, need N548AB replacement?

usually, mechanical/assembly reasons

You do realize there are 0 ohm resistors out there, full ceramic resistors that have a single black line on it... why use it when a bare wire works...

Just that when they have multiple SKUs using the same PCB it's easier to replace different parts than retooling the pick and place with jumpers.
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Old Today, 06:27 PM   #75
Agent24
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Default Re: Catapillar ECU repair, need N548AB replacement?

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Originally Posted by CapLeaker View Post
Look at my first post. It is clearly a fairchild device. It's heat sinked to the casing, not to the board.
Oh I must have missed that.
It could possibly be designed to draw heat up the pins and dissipate out through the back plate?

I've seen mini heatsinks on a slot A motherboard that were soldered to the board.
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