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Old 15th March 2008, 02:22 AM   #1
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Default Blowing supply when turned up?

Hey everyone, I'm new here and have a question.

I have a Power Acoustik 2400 watt "supposily" 1-ohm bridgeable amp that was given to me a few years ago. Guy was just going to throw it away, so I took it.

The history on the amp is it has two inputs for the power supply. (Two seperate B+, Rem, Gnd.) Kinda weired, but at one time, one side was hooked up backwards, and that pretty well ended one side of the amp.

When received the IRFZ44N were blown on one side, which I assume was the side that was hooked up wrong. So I replaced all of them on that side. Also I checked the resistors that were on the gate (I think) and they all checked out ok. I can't remeber if they were 10 ohm, or 100 ohm, but they all checked out ok.

So when I powered up the amp, it played fine at low volume, but the side I replaced the IRFZ44N seemed to be getting extremely hot! I decided what the heck and give it some more volume, and then two of the IRFZ44N blew again. So obliviously there is something else wrong with it.

Also it was just one channel that blew, the other channel kept playing, but didn't sound to clean.

What else can I check? Could I have a problem with some of the electrolytic capacitors?

Also I have access to a DVM, and oscilloscope if needed!
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Old 15th March 2008, 02:28 AM   #2
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Location: Louisiana
If it has PNP driver transistors driving the power supply FETs, one or both in the defective power supply is likely open.

Can you post a photo of the guts or give a model number?
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Old 15th March 2008, 04:30 AM   #3
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Ok all the amp has on it far as model goes is "1-Ohm 2400-2"

Here are some pics with captions. Sorry if the pics are bad, cell phone is all I have.

View of the amp

Click the image to open in full size.

Here are the two power inputs. It seems this amp is almost two amps built into one.

Click the image to open in full size.

Ok, here is all the good stuff. There is a board on there with I have marked with SEE POST. It's just some break out board that is covered in some potting compound! They really didn't want you to see or work on this?? Any ideas?

Click the image to open in full size.

Back side of amp.

Click the image to open in full size.

Here is a pic of the toasty irfz44n.

Click the image to open in full size.
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Old 15th March 2008, 12:28 PM   #4
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Join Date: Nov 2003
Location: Louisiana
Pull the 8 FETs in that half of the amp. With the amp powered up, measure the DC voltage on the gate's solder pads (all 8 gate pads). Place the black meter lead on the ground terminal of the amplifier when taking the readings. Post the voltage read from the pads.

The gate pad is the solder pad where the first leg of the FET is soldered to the board.

You need to insert a 10 amp fuse in the power line feeding the amp to help prevent damage. You should have the amp clamped to the sink while testing. If that's not possible, closely monitor the temperature of the components that are normally clamped to the heatsink.
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Old 15th March 2008, 04:09 PM   #5
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I pulled all 8 FETS, and connected the amp to a 14.4v supply just like if it was running in a car.

All 8 gates read a voltage of 4.2v. I measured the good side, it they were only reading .38v. So then I traced the gates through the 100 ohm resistors, and they all go to two pins on the board that is covered in a potting compound. (I was afraid of this!)

Click the image to open in full size.

This board has one of these on each side. So I took measurements from the good said, and bad side, and here is what I got.

Good Bad

pin1= .87v------ .9v
pin2= .38v------ 4.2v (GATES)
pin3= .38v------ 4.2v (GATES)
pin4= 13.8v-----13.8v
pin5= gnd------- gnd
pin6= gnd------- gnd
pin7= gnd------- gnd
pin8= 13mv----- 16mv
pin9= 23mv----- 23mv
pin10= 35.4v----- 1.08v
pin11= 11.8v----- 1.08
pin12= 0v--------- 0v
pin13= 1.02v----- .87v
pin14= 1.25------ .1.05

I believe my problems might stem from this board. What do you think?

If so, I'll try to find a way to remove the potting compound from this board so I can try to access it. For some reason they didn't want you getting in there.
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Old 15th March 2008, 04:32 PM   #6
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Location: Louisiana
It appears that the amp has regulated power supplies. The 4.2v on the output of the board is a good thing. It means the drivers are probably intact. The good side probably has a lower reading because the duty cycle has been reduced. The duty cycle is reduced as the rail voltage reaches its target voltage (which appears to be ~35v here).

If there are no gate resistors that are out of tolerance, the drive circuit feeding the FETs appears to be OK.

Generally, when the power supply blows, it's due to excessive current draw from the secondary side of the power supply. This can be caused by shorted/leaking outputs, shorted rectifiers, broken connections in the bias circuit or a defective transformer. If you replace all 8 FETs and the amp still draws excessive current, you need to check all of the above.

You can do a quick check of the output transistors. Measure the resistance between the legs of each transistor. There should be no transistors that read near zero ohms between the legs of an individual transistor. You can compare the readings between the good and bad channels. Do this with no power applied to the circuit.

After replacing the FETs, insert a 10 amp fuse in series with the B+ line. If it blows, the amp is likely drawing excessive current and you need to do more troubleshooting. Have the transistors clamped to the sink when you power it up initially. If they're not clamped to the heatsink, it takes only seconds for the FETs to fail if there is a problem.
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Old 15th March 2008, 10:17 PM   #7
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Quote:
Originally posted by Perry Babin
You can do a quick check of the output transistors. Measure the resistance between the legs of each transistor. There should be no transistors that read near zero ohms between the legs of an individual transistor. You can compare the readings between the good and bad channels. Do this with no power applied to the circuit.
When you say output transistor, do you mean the TIP35 and TIP36?

Also is it possible to just put a few IRFZ44 in for testing purposes only? Or do all the banks need to be full?

I have some IRFZ44's on order now.
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Old 15th March 2008, 10:27 PM   #8
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Join Date: Nov 2003
Location: Louisiana
You can use fewer than 4 per bank. It will be easier to blow them (compared to 4/bank) but all you need is 1/bank. If you use a 10 amp fuse and clamp the transistors to the sink, 1/bank may survive even if there is excessive current draw.

Don't try to re-use the power supply FETs that were in the amp when it failed. It's VERY rare that any of the FETs survive when the supply fails.

The TIP35c/36c are the output transistors.
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Old 16th March 2008, 12:16 AM   #9
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Ok thanks for your help. I've got some new 44's on there way from digikey. I had some spares, but I left them at my last place of employment. Hopefully I can get to it soon. I'll check everything else you mentioned. Again thanks!
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Old 16th November 2010, 04:50 AM   #10
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Join Date: Nov 2010
Quote:
Originally Posted by GSXR1181 View Post
Hey everyone, I'm new here and have a question.

I have a Power Acoustik 2400 watt "supposily" 1-ohm bridgeable amp that was given to me a few years ago. Guy was just going to throw it away, so I took it.

The history on the amp is it has two inputs for the power supply. (Two seperate B+, Rem, Gnd.) Kinda weired, but at one time, one side was hooked up backwards, and that pretty well ended one side of the amp.

When received the IRFZ44N were blown on one side, which I assume was the side that was hooked up wrong. So I replaced all of them on that side. Also I checked the resistors that were on the gate (I think) and they all checked out ok. I can't remeber if they were 10 ohm, or 100 ohm, but they all checked out ok.

So when I powered up the amp, it played fine at low volume, but the side I replaced the IRFZ44N seemed to be getting extremely hot! I decided what the heck and give it some more volume, and then two of the IRFZ44N blew again. So obliviously there is something else wrong with it.

Also it was just one channel that blew, the other channel kept playing, but didn't sound to clean.

What else can I check? Could I have a problem with some of the electrolytic capacitors?

Also I have access to a DVM, and oscilloscope if needed!
did you ever get this amp fixed?? if so, i would liek to buy it from you
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