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Is this installed right, a Mosfet? #5276331 11/24/19 02:44 PM
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daves66nova Offline OP
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I don't know about electronics. i had someone install these 2 . Are they backwards, as in the metal part needs to be facing the heat sink? The middle of the heat sink has a threaded hole which, when the casing goes over the circuit board, the screw pulls the heat sink and the 2 pieces towards the aluminum casing. He said that I need to put some of that paper to isolate the metal side from the casing.

mosfet.jpg

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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276361 11/24/19 03:18 PM
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sdowney717 Offline
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Everything about that looks bad. Were the original mosfets facing this direction?

When you replace transistor components, they can only go back in one way, no other way will function.
I have never seen them reversed like your showing, then to be attached to a heat sink bar. And I see the yellow insulating tape to the left, are there more mosfets or diodes over there?

There should be a metal clamp that goes across the mosfets and then they are tightened against the heat sink with a screw into those threaded holes.

The person who did this, do they know about electronics repair?

Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276368 11/24/19 03:24 PM
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Dave9 Offline
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You were right to question it, normally transistors would be put next to a heatsink like that to make use of it by having them rotated 180'.

I assume there is something else heatsunk to the other side or behind that yellow tape?

In this case no, the transistors appear to be soldered in with the correct orientation because of the silkscreen on the PCB. See how it has the double line on one side? That is the side the 'fet heatsink tab goes on.

Why they did it like that? Well something is not designed well or some error was made in best design practices.

If you want to be sure which way they go and rule out design errors, trace the circuit to see where each pin of the transistors goes.

Lastly that soldering job is horrendous. There should be no muck and half wetted/cold solder on top. The top of the PCB should have been cleaned then solder added only to the bottom of the PCB when soldering in the new 'fets.

Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276380 11/24/19 03:32 PM
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Mr Nice Offline
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I agree the guy did a subpar job.

Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276477 11/24/19 05:29 PM
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The thermal tab of a MOSFET in TO220 is often tied to the drain of the device...I would be willing to bet that those two FETs are not intended to be common drain and that connecting them would be disastrous, but I'd have to see a schematic to be sure.
It would have been good to have a pic of the board before the surgery to see what it looked like then!
Looks like a common pinout for FETs in TO220 is G-D-S (gate-drain-source) when the pins are pointing down and the plastic "belly" is facing you...reversing that would certainly not be functional.
Are there screw holes behind the FETs? Can you see what the part numbers are on them?
Has any other surgery already been performed on this board?


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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276517 11/24/19 06:40 PM
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Errtt Offline
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It just doesn't seem to look right, to me. If you could refer to a schematic.
Even if it was right (I still think it isn't), I would pull them, do a bit of cleaning and do a better solder job.

Re: Is this installed right, a Mosfet? [Re: Dave9] #5276659 11/24/19 09:30 PM
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dk1604 Offline
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Agree with Dave9 that based on the silkscreen on the PCB, the transistors appear to be in the correct orientation. With that in mind and from your description it sounds like the case itself is the actual heatsink and metal bar in the photo is primarily to pull the transistors against the case. The "paper" your friend is referring to is a thermally conductive insulator. See the following link for examples:

https://www.mouser.com/Thermal-Mana...1x7n?Keyword=to220+insulator&FS=True

Also agree that the soldering job does not look the best and I would at least verify with a multimeter that there are no solder bridges between the pads. Redo them if you have any soldering experience.

Re: Is this installed right, a Mosfet? [Re: Virtus_Probi] #5276718 11/24/19 11:58 PM
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daves66nova Offline OP
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Originally Posted by Virtus_Probi
The thermal tab of a MOSFET in TO220 is often tied to the drain of the device...I would be willing to bet that those two FETs are not intended to be common drain and that connecting them would be disastrous, but I'd have to see a schematic to be sure.
It would have been good to have a pic of the board before the surgery to see what it looked like then!
Looks like a common pinout for FETs in TO220 is G-D-S (gate-drain-source) when the pins are pointing down and the plastic "belly" is facing you...reversing that would certainly not be functional.
Are there screw holes behind the FETs? Can you see what the part numbers are on them?
Has any other surgery already been performed on this board?
I wish I had a schematic. This is a Crane Cams HI-6 automotive ignition box. This guy said he worked at an electronics repair store before it closed. I don't see any holes on the heat sink for the 'fets. No other work has been done on this. Here's the other side

hi6.jpghi6-2.jpg

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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276763 11/25/19 03:27 AM
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Looks like he gouged the board trying to get through the conformal coating on the left FET! shocked2


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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276774 11/25/19 04:47 AM
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A total mess. The foils need to be checked because they look cut to me and some are missing. . Never seen such a shoddy repair like that, everything's wrong. Looks like there should be some kind of heatsink fastened to those threaded holes to the metal back of those FET'S. They look orientated correctly but I would still verify. Good solder joints should look like small "Hershey's Kisses".

Last edited by Lubener; 11/25/19 04:56 AM.

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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5276858 11/25/19 08:14 AM
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That looks terrible. No way that guy did soldering repair in his past. Unless he was drunk when he did that.


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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5277205 11/25/19 04:44 PM
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daves66nova Offline OP
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Can someone here maybe fix this?


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Re: Is this installed right, a Mosfet? [Re: Skippy722] #5277756 11/26/19 09:06 AM
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Virtus_Probi Offline
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Originally Posted by Skippy722
Looks like he gouged the board trying to get through the conformal coating on the left FET! shocked2

I'd bet the pins on that FET were shorted by excess solder and he used an Xacto knife to isolate them again.
It's hard to tell, but it looks to me like some of the traces on the board are cut or at least damaged (somebody else mentioned the same thing). You can re-establish the connections with some solder or maybe a bit of wire soldered down (I tend to use long wire leads from discrete resistors that I have previously trimmed), but that might not be very reliable in an automotive environment.
Sorry to say it, but it looks like a hack job to me.


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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5278794 11/27/19 11:16 AM
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daves66nova Offline OP
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So can anyone here fix this for me? I'll pay some.


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Re: Is this installed right, a Mosfet? [Re: daves66nova] #5281307 11/30/19 04:23 PM
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dk1604 Offline
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As nobody has responded here yet, you might want to ask your question over on the "Automotive Electrical" forum or even the "Mechanical/Maintenance Forum". Might get more "eyes" on it over there as I kind of view "Consumer Electronics" as discussing televisions and smart phones rather than ignition systems.

Found your original thread discussing replacements for the transistors titled "Looking for a better quality Mosfet". Did you ever find a "New old stock" replacement for the obsolete IGBT?

Do you know for certain that the coil isn't shorted?

Cleaning up the soldering job, and even repairing the traces on the PCB should it be necessary, is pretty straight forward for anyone with reasonable soldering skills. You might be able to find someone to help at one of your local Maker spaces. The real issue is whether or not there is more damage beyond the transistors. The ignition module may still not work after swapping the transistors - especially if one of those transistors is a cross and not the exact same part as original.



Last edited by dk1604; 11/30/19 04:24 PM. Reason: fix typo
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