Amplifier repair
02-29-2004, 07:16 PM
#1
Guest
Posts: n/a
Posted this on Carsound, but don't seem to be getting much help there, and I know there are quite a few guys who know their stuff here so here goes...
I picked up a blown MTX 2300x amplifier for a learning project. I was told the previous owner was hooking up a capacitor when the amp kicked the bucket.
I hooked up the amp and it powers up fine. Here's where it gets interesting though...The left channel will read 44VDC for approx 2-3 seconds, drop to 0v, then back up to 44VDC in a cycle. The right channel has a very small output.
I pulled the board out, and the center row of fets (4) along the top side read a dead short from pin to pin still in the board. I unsoldered the 4 and only 1 reads a short now, the other 3 read OL except accross the internal drain diode from drain to source.
So I have found one problem, how can I check for others? Is there a method for testing the power supply to ensure it is functioning fine? Any other tests I can perform on the amp while I have the board out? I have a DMM with diode/capacitor check, and a scope if I need it.
Thanks guys.
[ February 29, 2004, 08:18 PM: Message edited by: Kilowatt ]
I picked up a blown MTX 2300x amplifier for a learning project. I was told the previous owner was hooking up a capacitor when the amp kicked the bucket.
I hooked up the amp and it powers up fine. Here's where it gets interesting though...The left channel will read 44VDC for approx 2-3 seconds, drop to 0v, then back up to 44VDC in a cycle. The right channel has a very small output.
I pulled the board out, and the center row of fets (4) along the top side read a dead short from pin to pin still in the board. I unsoldered the 4 and only 1 reads a short now, the other 3 read OL except accross the internal drain diode from drain to source.
So I have found one problem, how can I check for others? Is there a method for testing the power supply to ensure it is functioning fine? Any other tests I can perform on the amp while I have the board out? I have a DMM with diode/capacitor check, and a scope if I need it.
Thanks guys.
[ February 29, 2004, 08:18 PM: Message edited by: Kilowatt ]
02-29-2004, 07:54 PM
#3
Guest
Posts: n/a
OK. But the unit powered up fine with them in the board, it just ouput the full voltage (44VDC)on the left channel (same side as the blown fet). I'm just looking for a way to test to see if that was the only part that cooked, and to make sure the power supply is good.
Thanks.
Thanks.
02-29-2004, 08:44 PM
#5
Guest
Posts: n/a
LOL...OK, I'll try and explain better.
I hooked the amp up in the car to my H/U. No speakers were attached. I metered the speaker terminals while the amp was on and read 44VDC on the left channel.
I took the amp out, and located a shorted fet on the left channel and removed all 4 (top center row in pic). I have not powered up the amp since.
Is there any other tests I can do while I have the amp appart? Or should I solder in the new fets and power it up? I am just worried something upstream may be toast as well, causing the fets to burn up. Can I somehow test the powersupply to make sure it is functioning properly?
Is it common for just the fets to burn up, and nothing else?
Thanks for the help.
I hooked the amp up in the car to my H/U. No speakers were attached. I metered the speaker terminals while the amp was on and read 44VDC on the left channel.
I took the amp out, and located a shorted fet on the left channel and removed all 4 (top center row in pic). I have not powered up the amp since.
Is there any other tests I can do while I have the amp appart? Or should I solder in the new fets and power it up? I am just worried something upstream may be toast as well, causing the fets to burn up. Can I somehow test the powersupply to make sure it is functioning properly?
Is it common for just the fets to burn up, and nothing else?
Thanks for the help.
02-29-2004, 10:25 PM
#6
Yankee
Join Date: Oct 2003
Posts: 3,599
Q: did either channel work after cap-tastrophy?
Q: does either channel follow volume control now?
Q: it would be nice if you had a variable DC source so you can bring up the voltage and see how the power supply is working
Multiple failures are common, if one channel is good then you can use it to diagnose the other channel.
Q: does either channel follow volume control now?
Q: it would be nice if you had a variable DC source so you can bring up the voltage and see how the power supply is working
Multiple failures are common, if one channel is good then you can use it to diagnose the other channel.
03-01-2004, 07:38 AM
#8
Guest
Posts: n/a
John-
Q1:neither channel has worked since I have had the amp. One channel read 44VDC in a 3 second cycle like I mentioned above, and the other sounded like it might work, but was shut off when the amp cycled off on the left channel.
Q2:I have not hooked the amp up since removing the fets. Should I replace the fets first, or just hook it up without them?
Q3:I have a variable DC source, I can hook it no problem once I have an answer for Q2.
Mister Steve, it is a solid DC output on the left channel, so there was barely a reading on AC.
Thanks guys.
Q1:neither channel has worked since I have had the amp. One channel read 44VDC in a 3 second cycle like I mentioned above, and the other sounded like it might work, but was shut off when the amp cycled off on the left channel.
Q2:I have not hooked the amp up since removing the fets. Should I replace the fets first, or just hook it up without them?
Q3:I have a variable DC source, I can hook it no problem once I have an answer for Q2.
Mister Steve, it is a solid DC output on the left channel, so there was barely a reading on AC.
Thanks guys.
