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Old 28th January 2012, 09:26 PM   #1
chipper is offline chipper  United States
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Default Rockford punch 500a2

I have a punch 500a 2 coming in on monday it's non working. I want to know if I can use MMBTA06LT1 & MMBTA56LT1 for replacements for the driver transistors? I remember a while back I had a power 551s that I used some of these in it and worked out good.

And for the channels what main components usually fail? Besides the output transistors? So if I drop in new ones I don't want the power supply to fail again. Thanks all
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Old 28th January 2012, 10:53 PM   #2
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Those should work fine. check with Perry to be 100%.

I usually use the MMBT3906 and the MMBT3904.

Besides the output fets, check the gate resistors, the source resistors, and the protection transistor and diodes. Marked 1A, 2A, 5D, A7 sometimes these fail, and sometimes smd resistors fail or go out of tolerance.

You need to get the amp and trouble shoot it to see what the problem is and go from there.
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Old 29th January 2012, 12:32 AM   #3
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Quote:
Originally Posted by chipper View Post
I have a punch 500a 2 coming in on monday it's non working. I want to know if I can use MMBTA06LT1 & MMBTA56LT1 for replacements for the driver transistors? I remember a while back I had a power 551s that I used some of these in it and worked out good.

And for the channels what main components usually fail? Besides the output transistors? So if I drop in new ones I don't want the power supply to fail again. Thanks all
A06/A56 shouldn't be an issue, rated for higher voltage and current.

Easiest solution not to blow out the supply is a current limit in B+. The other option is to check the gate signal before populating the outputs.

If the supply is trashed remove the fets, apply remote power and gnd then check the gate signals on the power supply fets.
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Old 30th January 2012, 12:14 AM   #4
chipper is offline chipper  United States
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Okay gotcha guys when it comes tomorrow morning.

May I ask? Why aren't the original power supply fets available anymore? (MTP75N05HD)?
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Old 30th January 2012, 12:30 AM   #5
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They are still available but hard to find and expensive. They are just obsolete or discontinued.

The IRF3205 is a better substitute anyway, you just have to change the gate resistors to 47 ohm and get your drivers changed and you will be good to go.

I would bet you have some shorted output fets in this amp unless someone just reversed the polarity and popped the power supply section.
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Old 30th January 2012, 12:30 AM   #6
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Probably an old design that was updated. Fairchild semiconductor should have a cross for that part(HUF75344P3).

Last edited by brandes.cm; 30th January 2012 at 12:46 AM.
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Old 30th January 2012, 02:11 AM   #7
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I'll stick with the 3205's plus I have them on hand. Would I have to change the driver transistors even if they aren't shorted? To be suitable for these mosfets.

Also where can I get some IRF9540's? I have 25 IRF540's already.
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Old 30th January 2012, 02:22 AM   #8
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You dont have to change the drivers they will work fine with the IRF3205's but for ultimate reliability since the power supply has failed I would reccommend changing them.

IRF9540's are available almost anywhere. Active parts from ebay or ARROW.COM has them pretty cheap. You can get them from mouser.com and alliedelec.com as well.

The last 300 I bought were from active parts on ebay. I have put them in at least 60 amps with no issues.
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Old 30th January 2012, 05:20 PM   #9
chipper is offline chipper  United States
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Hmm both channels are BLOWN! + a shorted power supply. It also appears this amp may have been worked on by RF? Did they still service the "A" series amps around 2001?
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Old 30th January 2012, 07:55 PM   #10
chipper is offline chipper  United States
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For Q7 & Q11 for the gate voltage I get 8 volts DC and for Q10 & Q9 I get 5.08 volts DC on the gate pads. So I'm better off replacing the drivers also right?
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