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#1 |
diyAudio Member
Join Date: Aug 2010
Location: Illinois
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I found that two IRF640N outputs (FET404 & FET6) were shorted, one on each side. I removed all fourteen to find the two, checking each one. None of the remaining twelve appear to be leaking. The TIP29C & TIP30C were checked in circuit, and are not shorted. All of the 10 Ohm gate resistors are ok. I presume the .1 Ohm, 5W resistors are ok, none are even remotely discolored.
I re-installed all of the IRF640Ns that appear ok and left out the two shorted ones at those above FET locations. The amp draws excessive current. I removed the four rectifiers and the amp idles at ~2A draw. Is that high for an unloaded power supply? Does this amp require all fourteen of the outputs to be good and installed or are there more areas I need to look at?
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Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer |
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#2 |
diyAudio Member
Join Date: Dec 2010
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replace all of them another one might be burned inside but not appearing shorted
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#3 |
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
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Did you check the components on the driver board? They often fail when the outputs fail.
I would expect the amp to work with one transistor missing from each side. 2A is high but doesn't necessarily mean that there is a problem.
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#4 |
diyAudio Member
Join Date: Aug 2010
Location: Illinois
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I checked the A92s and A42s in circuit and they are not shorted.
Should I check the smaller components?
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer |
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#5 |
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
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How much was the excessive current draw?
Did it draw excessive current as soon as remote voltage was applied?
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#6 |
diyAudio Member
Join Date: Aug 2010
Location: Illinois
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It does blow a 25A fuse shortly (~1.5 seconds) after remote voltage is applied. Once the draw begins, it climbs rapidly. I think it was close to ~30A when fuse blew.
With a limiting resistor in line with B+, the amp cycles on and off because the voltage drops too low for the amp to stay on but it does not blow a 15A fuse this way.
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer |
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#7 |
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
|
When it's cycling on and off, do you see rail to rail oscillation on any legs of the output transistors?
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#8 |
diyAudio Member
Join Date: Aug 2010
Location: Illinois
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I have not checked for that yet.
Where should I place the scope ground in this amp when I do?
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer |
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#9 |
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
|
You can probably use the primary ground.
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Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links |
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#10 |
diyAudio Member
Join Date: Aug 2010
Location: Illinois
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I re-installed the rectifiers.
With my 3 Ohm resistor and a 15A fuse in line with B+ the power light comes on with ~4 amp draw, however the voltage at the amp's terminals is ~8.5VDC and does not change much as I adjust my power supply from 12V-16V. Testing any of the three legs of the output located at FET18 shows nothing on the scope.
__________________
Tools - 1. TPI Scope Plus 440 2. B&K 2125 20MHz Dual Trace 3. Sorensen DCR20-50B 4. B&K 4011 5MHz Function Generator 5. Weller WESD51 6. A big hammer |
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