IRFZ44N Chip Question?

[Itsme]

Hello, I have a SPL CRM1200-2 and at least one of the IRFZ44n's are blown. So I am planning on replacing them all and just wondered if there is maybe a better chip to replace them with to get a few more watts out of this amp and what other modifications I would have to do like matching the outputs? I have heard it is possible to upgrade some amp's but I don't know to much about it. I would apreciate anybodys help with this.
Thanks.

[Itsme]

Here is a pic of the outputs.

[Itsme]

Here is another pic.

[Itsme]

Last pic.

[Perry Babin]

Unless you know an amp well, it's best to get the amp working properly with the original parts. After you 'know' that it's working properly, then you make the substitutions. It may cost a bit more but you don't have to waste time trying to determine if the replacements are the cause of the problem or if there is something else wrong with the amp.

The drive circuit on this amp 'should' be able to drive IRFZ48 FETs. They are rated for more current than the IRFZ44s.

Using a different FET will not cause the amp to make more than a few watts more (nothing audible). If the power supply FETs failed but the outputs didn't, the the Z44s may not be rugged enough. If the power supply died because the outputs failed, there's probably no reason to go to a different FET.

When you power up this amp after replacing the FETs, have them clamped tightly to the sink and have a 10 amp fuse in the B+ line.

If the outputs didn't fail, there may be another reason for the power supply failure. With the amp powered up, twist the transformer. If there are intermittantly shorted windings, the fuse will blow or you'll see sparks between the windings as you twist. You would need to find and insulate any shorted windings.

[Itsme]

The guy I got the amp from said he had put a bigger fuse in after 1 had blown... He thought he had it under a 2 ohm load bridged after hooking the woofers up wrong.

[Itsme]

To explain it more. I think it can only be bridged into a 4 ohm load and thats why he blew the fuse the 1st time. And then not being very smart, he put a bigger fuse in and smoked the IRFZ44N.

So should I order IRFZ48N's or go back with the IRFZ44N's? I agree with you Perry to get it working first, than modify if possible. But if it won't hurt anything to put a little stiffer FETS in then I would like to. What do you think?

[Perry Babin]

It's going to cost an additional $10 to get it working with the Z44s first then change them to Z48s. I think it's well worth the expense. The Z44s will not be damaged and can be used for other repairs if you'd like.

If I'm not mistaken, this amp has a regulated power supply and unless you have a 12v DC power supply with variable voltage and an amp meter, it may be difficult to tell if the drive circuit is able to turn the FETs off quickly enough at the maximum duty cycle. I think it will be OK with Z48s but I've never tried them in one of these.

Check the output transistors before you order parts. If you find any that read anything near 0 ohms between legs 2 and 3, pull them from the board and check them.


Before you replace the transistors, clean all of the black soot from the board. I'd suggest using acetone and a toothbrush. Don't use a transparent toothbrush. Acetone melts them. Do this outdoors. Read the label on the acetone if you've never used it.

[Perry Babin]

Do the power supply FETs have circuit board designations of Q41-Q49 (no Q45)?

[Itsme]

I will get both z44's and z48's. I checked all of the bigger output transistor's but I didn't test the smaller ones in between the z44's and the bigger outputs. Which I think are diodes (FMG222) and (TIP41C),(TIP42C).
All the output trans. were open between leg 2 and 3. Can you explain the maximum duty cycle shutting down the FET's? How can you tell if It has a regulated power supply? Is that the same as a PWM? I did post some pic's above of the multipin controller chips, also there was a white 4 pin chip next to them. Those control the power supply right?
I have a Yellow top Optima battery with inline fuse holder, But no way to make variable voltage. I do have several amp meters and 8 DMM's which 2 are Fluke's. I don't have Osciliscope, but am in the market for one. So do I need to buy a variable power supply? And yes to your question, No Q45. I think they use this same board for their higher wattage amp's, It look's like more Fet's could be added. (Empty slots). Anyway would you suggest I order any other parts to replace? like I see a couple of resistors that look like they have been hot. It's the small resistors in front of the Z44's. And any parts to upgrade after getting amp working? Thanks.