MOSFET Transistor replacement....

[AznGothic]

I have a car audio amplifier that would go straight to protect when powered up. I have gone through all the different components that would cause this and found two MOSFET's shorted. Seeing how these are ran in parallel I actually needed to replace 6 of them. I replaced three that were on the power side and left the three on the audio output side off the amp just to test it. No more protection light. So now I just need to replace the three on the audio output side and I should be golden. The MOSFET's are IRF640N. My question is, can these be replaced with a different MOSFET? I'm having trouble finding these for a cheap price and quick delivery.

 

[(*steve*)]

Are you sure you need to replace all of them?

Not that it's a bad idea, mind you.

But with just the 2 shorted ones replaced you have clearly powered it up to see if the protection light comes on. Have you tried seeing if the amplifier works? (preferably at low volume first)

 

[AznGothic]

Sorry, its a bit late and I didn't explain thoroughly. I replaced the one on the power side with one from the audio side and left the three audio ones out of the amplifier to see if it would turn on. So out of the six I desoldered, two were bad and I put three back in. From my understanding it doesn't matter if the MOSFET's match unless they are ran in parallel. So I tested the four good ones and picked three that were the closest matched. I'm not sure if I matched the correct attribute but I basically tested them with a multi meter set to diode and picked the three that had the closest forward voltage.

I have not tested the amplifier for audio output yet because of the three MOSFETs that are missing on the audio output side. Technically I only need to replace two of them but would rather replace all three since they have to match. My problem is I'm having a hard time finding them for a reasonable price/shipping time. Either they have a reasonable price but would take weeks to receive or they are way overly priced but I would get them in a few days. So I'm wondering if there is an equivalent MOSFET I can use to replace the three IRF640N's.

 

[(*steve*)]

It would help telling us where you are.

In the US, the first place I looked had them at between $1 and $3 (depending on package) plus freight.

http://www.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=IRF640N

 

[AznGothic]

I'm in the USA. Texas to be more specific. I clicked the link you posted. What is the difference between the IRF640NPBF-ND, IRF640NLPBF-ND, IRF640N-ND and the IRF640NL-ND? From the looks of it all the specs are the same but the packaging is different? The only numbers I see on the ones I pulled out are IRF640N, 813P, EG and 9M.

 

[AznGothic]

Ok I did some digging and from what I'm understanding the L in the model number just stands for low profile. Still not sure what the difference is between the IRF640NPBF-ND and the IRF640N-ND.

 

[MrEE]

PBF stands for lead free (or Pb-free), otherwise the same component

 

[(*steve*)]

Well, we need to know what package the original devices are.

Can you post a picture of one of them?

Some of that alphabet soup refers to them being for lead free boards (PBF)

There's 2 main types of packaging, TO-220 and D2PAK. Since you were able to remove yours, I imagine they are TO-220. They have 3 leads coming out of one end of a black epoxy rectangular prism with a metal tab on the back of it which extends beyond the epoxy in the direction opposite the leads. Most importantly, there is a hole in the metal tab where it is attached to a heatsink.

 

[AznGothic]

Thank you MrEE. That clarifies what the different extra numbers are.

Steve, I can take a picture of it but I left it at work. It is exactly how you described it though. The three leads (G, D, S) out the bottom of a black epoxy square with a metal tab on the back that extends upwards with a hole in it. In this application the hole isn't being used though. But yes it is exactly how you described it. What does the D2PAK look like?

 

[(*steve*)]

What does the D2PAK look like?

Similar, but different.

3 leads, but the centre one is cut off, the other two are bent down to the level of the tab at the rear. The tab is similar but far shorter (extending only a few mm beyond the case) and it has no hole in it. The device is soldered flat to the board (yes, the tab is soldered to the board)

Google will show you

 

[AznGothic]

Ya, I'm not one of those that are lazy and don't make use of Google I looked it up but they all a looked the same lol. Thank you for the info. So I definitely have the TO-220 since the center lead isn't cut and there's a hole in the tab. Does it matter if I get the PBF or not?

 

[(*steve*)]

I looked it up but they all a looked the same lol.

black thing with legs

Does it matter if I get the PBF or not?

Not unless you know you have lead free solder and that the board was lead free, and you want to keep it that way.

 

[AznGothic]

Ah, so being lead free doesn't really affect it at all except being lead free. Well my solder isn't lead free and I doubt this amplifier is either. I'm using silver bearing solder.

And no, I'm not like my gf where every car that is blue looks the same lol. I think all the images I was seeing were just stock photos of a typical TO-220 . Either way I learned a lot from you guys and I thank you for that And the site linked also has the high temp high voltage capacitors I need to fix a TV so that's a bonus! You guys have been a great help!