help with 551s

fosgatefan · 4th March 2009, 03:40 AM

Hello everyone and anyone that can help me

I have a rockford 551s amp that wouldnt turn on. I checked the power supply fets and found that all four of the 3205s were shorted. I took off the old ones and in the mean time i pealed back the copper on 2 that holds these to the heat sink and I chipped transister d2 trying to get a fet off. does anybody know how I can fix the copper I am assuming glue? also I am looking for a part number for d2 any help would be appreciated.

Thanks

Perry Babin · 4th March 2009, 10:45 AM

There's no way to repair the insulator. You'll have to cut the end of the strip off, make a clamp for the new transistors and clamp them down. You'll have to insert an insulator under the new transistors so they don't short to the heatsink.

In the future, desolder them by heating the insulator from the bottom with a small butane torch (like the one from Radio Shack).

MMBZ5257B
http://sigma.octopart.com/4958/datas...-MMBZ5257B.pdf

fosgatefan · 4th March 2009, 11:17 PM

I will defiantly do that in the future. I found this heat pad on digi key BER110-ND or BER174-ND do you think that it will work? and what would you recommend using for a clamp.

Thank you for your help.

Perry Babin · 5th March 2009, 12:32 AM

I'd recommend 3/8" x 3/4" aluminum bar stock. It should look something like the attached photo.

The screws are screwed down to the bottom of the screw hole and the nuts are used to tighten the clamps.

I'd also recommend using a double-sided foam or silicone tape between the clamp and the transistors.

For an insulator, I'd recommend mica and heatsink compound. You can get a small tube of heatsink compound from Radio Shack.
http://search.digikey.com/scripts/Dk...&name=4671K-ND

fosgatefan · 5th March 2009, 10:13 AM

That sounds good, what about the center of the fet hole would it short out the fet if the screw touched the side of it being as how the screw is connected directly to the heat sink

fosgatefan · 5th March 2009, 10:13 AM

Ok disregard the last post I misunderstood that you said screw holes

Ill let you know how it turns out and if it works........ fingers crossed

fosgatefan · 8th March 2009, 08:04 AM

Perry,

I replaced the four 3205s and now the amp draws excessive current about a half amp at 7.7v I'm not sure where or what to check next. I removed and checked the NL251 and U1620R and it still draws .5 amp. I cant find these part numbers anywhere as I want to replace them.

Thanks, Lance

Perry Babin · 8th March 2009, 03:34 PM

What sort of power supply are you using?

What's the current rating of the supply?

Does it draw current if you don't apply remote voltage?

fosgatefan · 8th March 2009, 04:11 PM

The power supply is a TENMA 72-2080 and the current is 3.2A on the meter. I removed the remote voltage and It still draws too much current. I was thinking about removing the 3205s one by one but they all tested good when putting them in.

Perry Babin · 8th March 2009, 04:14 PM

Did you check the gate resistors and the driver transistors for the IRF3205s?

4th March 2009, 03:40 AM	#1
fosgatefan diyAudio Member Join Date: Mar 2009	help with 551s Hello everyone and anyone that can help me I have a rockford 551s amp that wouldnt turn on. I checked the power supply fets and found that all four of the 3205s were shorted. I took off the old ones and in the mean time i pealed back the copper on 2 that holds these to the heat sink and I chipped transister d2 trying to get a fet off. does anybody know how I can fix the copper I am assuming glue? also I am looking for a part number for d2 any help would be appreciated. Thanks

4th March 2009, 10:45 AM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	There's no way to repair the insulator. You'll have to cut the end of the strip off, make a clamp for the new transistors and clamp them down. You'll have to insert an insulator under the new transistors so they don't short to the heatsink. In the future, desolder them by heating the insulator from the bottom with a small butane torch (like the one from Radio Shack). MMBZ5257B http://sigma.octopart.com/4958/datas...-MMBZ5257B.pdf __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

8th March 2009, 03:34 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	What sort of power supply are you using? What's the current rating of the supply? Does it draw current if you don't apply remote voltage? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

8th March 2009, 04:14 PM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Did you check the gate resistors and the driver transistors for the IRF3205s? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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4th March 2009, 11:17 PM	#3
fosgatefan diyAudio Member Join Date: Mar 2009	I will defiantly do that in the future. I found this heat pad on digi key BER110-ND or BER174-ND do you think that it will work? and what would you recommend using for a clamp. Thank you for your help.

5th March 2009, 10:13 AM	#5
fosgatefan diyAudio Member Join Date: Mar 2009	That sounds good, what about the center of the fet hole would it short out the fet if the screw touched the side of it being as how the screw is connected directly to the heat sink

8th March 2009, 08:04 AM	#7
fosgatefan diyAudio Member Join Date: Mar 2009	Perry, I replaced the four 3205s and now the amp draws excessive current about a half amp at 7.7v I'm not sure where or what to check next. I removed and checked the NL251 and U1620R and it still draws .5 amp. I cant find these part numbers anywhere as I want to replace them. Thanks, Lance

8th March 2009, 04:11 PM	#9
fosgatefan diyAudio Member Join Date: Mar 2009	The power supply is a TENMA 72-2080 and the current is 3.2A on the meter. I removed the remote voltage and It still draws too much current. I was thinking about removing the 3205s one by one but they all tested good when putting them in.

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