ST1000D class D amplifier fried my subs! - diyAudio
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Old 6th October 2012, 10:48 PM   #1
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Join Date: May 2012
Default ST1000D class D amplifier fried my subs!

OK, so I purchased a used Memphis Audio Amp, ST1000D class D amplifier and upon connecting it to my two Memphis subwoofers, the green power light came on and everything seemed to be in working order. I hadn't even switched the subs on, through my head unit, when I started smelling he voice coils burning! I quickly disconnected the speakers and rechecked my wiring.

I am not a newbie as far as car audio installation so I checked and double checked, with my multimeter, that the subs were wired to have a final impedance of 4ohms at the amplifier.

The subs are 2 X 12" DVC 4ohm Memphis audio subs with a rating of 500 RMS each! This amp should have been perfect, in fact, I could have lowered the final impedence through the sub wiring but I know that this particular amp is a mono block amp with two sets of speaker connections, internal wiring drops the impedence to 2ohms.

So after double checking my wiring I tried again, this time the subs were fully extended and held in an upward position and the voice coils on both subs were fried completely!!! Anyway, what is the problem with this amp?

Can anyone suggest what to check first? I checked for any obvious burnt transistors or resistors but none of them seemed to be toast! I also used my multimeter to check the power FETS and the output transistors and they all read normal! I'm a little new at this amp repair thing so can anyone give me some advice a to what I should check next? It obviously is pushing out WAAAAY TOO MUCH DC CURRENT!
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Old 7th October 2012, 08:11 AM   #2
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This is car audio equipment so try the car audio forum.
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Old 7th October 2012, 02:29 PM   #3
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You said this is a "car audio" forum correct? Well, the last time I checked, memphis CAR audio ONLY make components for CARS This is a CAR AUDIO amplifier and and actually, I did find the power FET transistors and 4X 22 ohm ate resistors had been blown! I actually checked every gate resistor and every power and output transistor prior to installing it in my CAR. They all read functional on my multimeter so what would have caused this?

I don't want to replace all of these transistors to have them all fry again! That's the extent to my amp repair knowledge, the transistors, the driver board, and the gate resistors. Anyone else that can actually help me with my CAR AUDIO AMP REPAIR situation would be greatly appreciated!
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Old 7th October 2012, 03:40 PM   #4
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No, he said check the CAR AUDIO FORUM here:Car Audio - diyAudio
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Old 7th October 2012, 03:53 PM   #5
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Check for DC out of the amplifier as this will fry a speaker very quickly if it is high.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 9th October 2012, 07:16 PM   #6
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Thank you for that helpful advice! I measured the speaker wire connections at the amps terminal for DC current and it measured 132 volts. Is this normal? I finally pulled the amp apart and I found the the IRF3205 FET transistors were in fact bad! None of the gate resistors were though? Isn't that uncommon?

I checked the output transistors as well and they too were bad! The concern I'm having is that prior to connecting these subs to the amp I checked with a multimeter and all output and power transistors were fine! The green power light remained on during this entire event as well! The internal fuses (2 x 40) blew but the protect light never came On! I'm worried that once I replace the power and both sets of output transistors, it will only repeat the same occurrence? What else could I check with the multimeter once the new transistors are in place?

I also have checked the driver board and found the 2 or 3 X A1266's were fried too! I dont own a oscillator so what other ideas can anyone give me to avoid frying ANOTHER pair of subs?

Last edited by ALLMemphisCarAudio; 9th October 2012 at 07:21 PM. Reason: Forgot info
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Old 10th October 2012, 06:09 AM   #7
Mooly is offline Mooly  United Kingdom
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Moved to car audio.
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Old 10th October 2012, 09:22 AM   #8
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It's odd that you would have 132v on the speaker terminals if the 3205s had failed. If they had failed, the amp shouldn't be able to produce any rail voltage. Are you sure that you checked them correctly?
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Old 10th October 2012, 03:17 PM   #9
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Thanks for responding Perry, I know your very busy but if anyone can help me figure this out, it's you!

I tested the DC voltage immediately after the subs went up in a smoke of glory The 3205's could've very well failed after I tested the voltage or I could've tested it incorrectly! Interestingly enough, prior to connecting the subwoofers to the amp, or installing it into the vehicle, I did a quick test with my multimeter.

I checked the 3205's and their gate resistors, the A1266's on the driver board, the ones that power the 3205's, and both sets of output transistors(9640's/640's), along with their gate resistors. Upon powering up the amp, remote wire attached, the green light came on. Still being inexperienced in amp repair, I assumed nothing was wrong when the green power light comes on! I shouldn't have trusted a 5 cent L.E.D. for an accurate assumption with a pair of $500 subs on the line, another expensive lesson learned!

Within 30 seconds of having everything connected, the subs fully extended upward, made a POP sound, and both voice coils overheated instantaniously! Unfortunately, the subs will require a complete overhaul to work again.

At this point, I've ordered all new 3205's, new 9640's, new A1266's and new 640's. I believe the two YG225C2 AND the two YG225N2's are OK, regardless, I can't find replacements for them anywhere??? Can ANYONE tell me if there is a new part#, interchangeable part, or even where I can find these?

Once I've replaced these parts, I will post my multimeter readings on this thread, using your very helpful work sheets perry, I want to be positive that I didn't miss anything, before applying power to the amp again! Is there anything I can test or check while I'm waiting on these parts? I do have an extra ST1000D amp that I'm using for spare parts and to compare multimeter readings.

I know these amps can be VERY unforgiving if powered up, even if only one bad component is overlooked! Please keep an eye on this thread Perry, I trust any advice and assistance that your willing to give. I can't begin to thank you enough for the VERY helpful tutorials that you've, so unselfishly, provided for the "average Joe". I should have all the new parts soldered onto the amp's board, no later than Saturday morning. Thanks in advance to ANYONE that takes the time to help!

Last edited by ALLMemphisCarAudio; 10th October 2012 at 03:21 PM. Reason: NA
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Old 11th October 2012, 07:19 AM   #10
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Location: Louisiana
For replacement rectifiers, I generally use the MUR1620CT and MUR1620CTR.

Sometimes, driver board components on the audio output driver boards fail. There are low ohm resistors (1-4.7 ohms) that open. Sometimes the driver transistors fail.

If the driver boards are in sockets, remove the audio driver boards before applying power. If everything else on the board is OK, you should have ±rail on the 3rgd legs of the outputs and no voltage on the center legs.
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