The following are the most likely suspects:
Shorted/leaking output transistors
Shorted rectifiers
shorted windings on the transformer
shorted inductor between the rectifiers and the filter caps (if it has one)
If you pull the rectifiers, it will break the connection between the power supply and the audio section. If there is no excessive current draw with the rectifiers out and the rectifiers are OK, the problem is in the audio section.
Shorted/leaking output transistors
Shorted rectifiers
shorted windings on the transformer
shorted inductor between the rectifiers and the filter caps (if it has one)
If you pull the rectifiers, it will break the connection between the power supply and the audio section. If there is no excessive current draw with the rectifiers out and the rectifiers are OK, the problem is in the audio section.
im thinking its the trasformer i get a reding of 0 ohms on it but i didnt take it out to test it !! would that matter ? plus does anyone know where i can get the mosfets for the power suply at 2 of them are fried !!
It's normal for the resistance across the windings of the transformer to be ~0 ohms. You're reading the DC resistance of approximately 1 foot of wire.
If one power supply FET is defective all power supply FETs have to be replaced.
If one power supply FET is defective all power supply FETs have to be replaced.
How to test Darlington BJTs?
Perry said:
"The TIP102/107s have Base, Collector and Emitter terminals. That's very different than FETs which have Gate, Source and Drain terminals. The test procedure is very different for BJTs and FETs.
The transistors you have are darlington BJTs with internal resistors and a reverse diode so they don't check like FETs or standard BJTs."
I also have a Soundstream 405 that suddenly started blowing the power fuses. Can anyone tell me what the procedure is for testing Darlington BJTs? I have access to a Fluke 87 multimeter, but no other test equipment.
By the way, I'm a complete novice when it comes to electronics. So specific instructions would be much appreciated. Thanks in advance!
Jim
Perry said:
"The TIP102/107s have Base, Collector and Emitter terminals. That's very different than FETs which have Gate, Source and Drain terminals. The test procedure is very different for BJTs and FETs.
The transistors you have are darlington BJTs with internal resistors and a reverse diode so they don't check like FETs or standard BJTs."
I also have a Soundstream 405 that suddenly started blowing the power fuses. Can anyone tell me what the procedure is for testing Darlington BJTs? I have access to a Fluke 87 multimeter, but no other test equipment.
By the way, I'm a complete novice when it comes to electronics. So specific instructions would be much appreciated. Thanks in advance!
Jim
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Sorry, my first request wasn't very clear. I've looked at the testing procedure for "Output Transistor Failure" on BCAE.com. At the end of the section for "Checking Bipolar Junction Transistors," it says "Both of these connections should also read as open. Any other readings indicate defective transistors. The only exception will be with darlington transistors. "
That's in addition to the quote from Perry that I put in my first post.
But I can't find any clarification on what the differences actually are when testing Darlington BJTs versus normal BJTs. Is the testing procedure the same? If so, then are the expected values on a multimeter different? If that's so, what are the expected values of good (and bad) Darlington BJTs? One other question - can these be tested while still on the circuit board?
Any help? Thanks!
Sorry, my first request wasn't very clear. I've looked at the testing procedure for "Output Transistor Failure" on BCAE.com. At the end of the section for "Checking Bipolar Junction Transistors," it says "Both of these connections should also read as open. Any other readings indicate defective transistors. The only exception will be with darlington transistors. "
That's in addition to the quote from Perry that I put in my first post.
But I can't find any clarification on what the differences actually are when testing Darlington BJTs versus normal BJTs. Is the testing procedure the same? If so, then are the expected values on a multimeter different? If that's so, what are the expected values of good (and bad) Darlington BJTs? One other question - can these be tested while still on the circuit board?
Any help? Thanks!
Thanks
Hello everyone, I'd just like to say a big thanks very much to everyone involved in this post.
I have suffered the exact same problem with this amp, it literally burned out my voice coils. I didn't check any components, but can add that my sub seemed to cut out irregularly before the damage ocurred. Once I was watching the subwoofer and it was working well, then the cone just pushed out to max and stayed for a few seconds, it went back and music resumed.
I took this to be a sure sign of a dc feed reaching the speaker.
Following this topic has led me to a complete solution to the problem and I have replaced the 6 npn and 6 pnp darlingtons on the sub channel only.
They came from RS components and are ST Microelectronics
TIP102
and TIP107
Not too difficult to do, just took my time and examined the results closely with a magnifier to check for and shorts.
Good job though, amp seems to be working well and the bass sounds much better (of course this could be down to the new twin coil sub compared to my old single) and I'm happy.
Thanks again all
Hello everyone, I'd just like to say a big thanks very much to everyone involved in this post.
I have suffered the exact same problem with this amp, it literally burned out my voice coils. I didn't check any components, but can add that my sub seemed to cut out irregularly before the damage ocurred. Once I was watching the subwoofer and it was working well, then the cone just pushed out to max and stayed for a few seconds, it went back and music resumed.
I took this to be a sure sign of a dc feed reaching the speaker.
Following this topic has led me to a complete solution to the problem and I have replaced the 6 npn and 6 pnp darlingtons on the sub channel only.
They came from RS components and are ST Microelectronics
TIP102
and TIP107
Not too difficult to do, just took my time and examined the results closely with a magnifier to check for and shorts.
Good job though, amp seems to be working well and the bass sounds much better (of course this could be down to the new twin coil sub compared to my old single) and I'm happy.
Thanks again all
I've been known to speak too soon
Right, well, erm...
I better let people know that my amp still has a problem.
Yesterday, it just cut out whilst I was driving. Both main fuses had blown.
I theorise that this is a recurence of the original fault. This time it blew the fuses instead of completely melting the voice coil of the subwoofer. I think maybe the higher capacity of the new sub has meant that when it goes DC, too much current is drawn by the amp and the fuses failed.
I'll update further if I get it fixed.
Good day
Right, well, erm...
I better let people know that my amp still has a problem.
Yesterday, it just cut out whilst I was driving. Both main fuses had blown.
I theorise that this is a recurence of the original fault. This time it blew the fuses instead of completely melting the voice coil of the subwoofer. I think maybe the higher capacity of the new sub has meant that when it goes DC, too much current is drawn by the amp and the fuses failed.
I'll update further if I get it fixed.
Good day
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