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Old 5th December 2006, 06:28 AM   #1
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Join Date: Nov 2006
Default my first broken amp... need help

ok this is an Audiobahn A18001DT that just died one day
so I took it to the local shop that sat on it for at least 5 weeks
now I'm out $25 bucks and not even sure he looked at it
after searching in vain for a better shop I decided to at least
look at it before sending it off to the factory repair shop $$$
at first glance everything appeared fine then I noticed a black
smudge near 1 of the FB31N20D mosfets? well upon a web
search I happened to find this site and tried to use the threads to guide me through the way to fix this ^@%@^% amp
sorry I'm very frustrated and rambling on
anyway I've relaced the 10 FB31N20D's- only the one was slightly
higher on the bench test 0.81 Ohms compared to 0.68 for the rest
I also checked the resistors nearby- all very consistant so I thought it would fire right up- wrong again- nothing but the protect light mocking my pain... back to the old forum board
I found this one helpful (NEW FETS INSTALLED, NO POWER) but
can't solve the problem of low voltage at the KA3525A PCM?
so here are my reading on the old DMM
PIN1: 0
PIN2: 5.03
PIN3: 0.01
PIN4: 0.18
PIN5: 2.25
PIN6: 3.44
PIN7: 2.24
PIN8: 0.37
PIN9: 3.37
PIN10: 0
PIN11: 4.09
PIN12: 0
PIN13: 9.86
PIN14: 4.09
PIN15: 9.86
PIN16: 5.03
my battery (with 5amp fuse) read 11.86
any ideas?
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Old 5th December 2006, 02:02 PM   #2
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Join Date: Jan 2005
Location: The Great Lakes
You need to check the drive transitors. I think there are 2 2sa1266, these always go when the input transistors blow. I fixed plenty HCT series that had this problem. I don't know if this audiobahn uses the same.
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Old 6th December 2006, 02:08 AM   #3
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I read about the input drivers but I'm not sure which is which
do they look similar to mosfets?
I've tried back tracing but this thing seems overly complicated
have not seen any 2sa1266
I'm new and learned what I know mostly off of here
I wish had a camera so I could post a picture
thanx for replying
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Old 6th December 2006, 08:02 AM   #4
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Join Date: Nov 2003
Location: Louisiana
Something is very strange about the numbers you posted. Pin 8 is the soft-start pin and is generally near 5v after the soft-start cap has fully charged. It's very low and I'd expect the IC to be off (producing no output on pins 11 and 14) but there is clearly some activity on the outputs.

The drivers are likely 2sa1023s ans s2c1027s. If I'm not mistaken, there are 8 drivers (4 for each set of PS FETs).

With the amp powered up, what is the DC voltage on pin 1 of the power supply FETs (only post one value if they're close). They should be near the voltage on the outputs of the 3525. You can follow the drive voltage from the outputs of the 3525 to the 3rd pin of the drivers and then from the first pin of the drivers to the outputs.

The 3525 on many of this style amp is powered via an NPN transistor. This is less efficient than using a PNP transistor and the voltage at the IC will be lower than you'd expect.
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Old 6th December 2006, 12:46 PM   #5
dB-r is offline dB-r  United States
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Join Date: Nov 2006
Just a heads up on buying those driver transistors if that indeed turns out to be the problem. I have not been able to find a place to buy those KEC parts A1266 1023 1027 etc but if you go to fairchild semiconductors website and use the cross reference they have some much less expensive parts that will substitute for those drivers. I have used them personally so I know they work as subs.

Here's the link:

http://www.fairchildsemi.com/crossref/crossref.jsp

I look them up with "Begins with" KTA1266 KTA1023 KTC1027 KTC3198 etc... Most common drivers and what not in car audio amps I have seen thus far.

Then go to your choice (mine is Mouser) to buy the fairchild parts, for probably much less than the KEC parts.

If someone has a good source for the KEC parts preferebly with online ordering and inventory, please email me sales@db-r.com
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Old 7th December 2006, 02:18 AM   #6
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Join Date: Nov 2006
Quote:
Originally posted by Perry Babin
Something is very strange about the numbers you posted. Pin 8 is the soft-start pin and is generally near 5v after the soft-start cap has fully charged. It's very low and I'd expect the IC to be off (producing no output on pins 11 and 14) but there is clearly some activity on the outputs.

The drivers are likely 2sa1023s ans s2c1027s. If I'm not mistaken, there are 8 drivers (4 for each set of PS FETs).

With the amp powered up, what is the DC voltage on pin 1 of the power supply FETs (only post one value if they're close). They should be near the voltage on the outputs of the 3525. You can follow the drive voltage from the outputs of the 3525 to the 3rd pin of the drivers and then from the first pin of the drivers to the outputs.

The 3525 on many of this style amp is powered via an NPN transistor. This is less efficient than using a PNP transistor and the voltage at the IC will be lower than you'd expect.
ok (if I understand) I do have four a1023 and four a1027
pins 1 (I assume lefthand facing print) on all are 4.36
pins 3 (righthand) are 3.91
uncertain if drivers and power supply FETs are one and the same
running low on 5 amp fuses LOL
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Old 7th December 2006, 09:05 AM   #7
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Location: Louisiana
The power supply FETs are clamped to the heatsink (likely IRFZ44s). The drivers boost the output current capability of the 3525 IC. The IC can't reliably drive that many FETs alone.

In place of fuses, you may want to use a current limiting resistor or an auto headlamp. The H6054 works pretty well. I use 2 ohm resistors. The large tubular ceramic 100w are the most foolproof. With fuses, they blow and you know there is a problem. With resistors (or the headlamp) you have to be more aware of the temperature of the components and the current being drawn (your power supply would need to have an amp meter). There are a few amps that won't power up through the resistor/headlamp but most will. Many amps pulse on/off a few times (likely low voltage protection in action) before they stay on.
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Old 8th December 2006, 06:37 AM   #8
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Quote:
Originally posted by Perry Babin
The power supply FETs are clamped to the heatsink (likely IRFZ44s). The drivers boost the output current capability of the 3525 IC. The IC can't reliably drive that many FETs alone.

In place of fuses, you may want to use a current limiting resistor or an auto headlamp. The H6054 works pretty well. I use 2 ohm resistors. The large tubular ceramic 100w are the most foolproof. With fuses, they blow and you know there is a problem. With resistors (or the headlamp) you have to be more aware of the temperature of the components and the current being drawn (your power supply would need to have an amp meter). There are a few amps that won't power up through the resistor/headlamp but most will. Many amps pulse on/off a few times (likely low voltage protection in action) before they stay on.

ok the IRFZ44 (16 of them) had 4.29 volts on pin 1 (lefthand)
11.38 on middle and zero on pin 3
the fuses were blowing because of my unsteady fumbling
I put black tape on my probe and rubbed off the tip- haven't used
up any more fuses
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Old 8th December 2006, 10:02 AM   #9
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Join Date: Nov 2003
Location: Louisiana
The amp should be producing rail voltage. Check the DC voltage on the ~1.5" inductor (the one that is not paired with any others - likely copper and green colored windings). Check all 4 terminals. At least one should have positive rail voltage and one should have negative rail voltage. These inductors have caused the failure of many amps. Check for broken solder connections and broken windings. Also look for any 'dust' where the windings meet. It's generally found where the terminal winding passes over the top of the coil. If there is colored dust (the color of the enamel insulation), the inductor may be failing or has possibly failed. Twisting the inductor slightly while the amp is on can help you find intermittantly shorted problem.

While you're checking the inductors, check the two next to the IRFB31n20s. They have the same problem.
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Old 8th December 2006, 11:56 AM   #10
dB-r is offline dB-r  United States
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This amp sounds similar to the amp I just got done working on, a Planet Audio TT2250D uses the exact same, 10 31N20d's and 16 IRFZ44's.

A problem I had, after installing all new fets, was that when I soldered in one of the new 31N20d's, the solder ran through the via, and puddled up on the other side of the board on the leg of the FET. Which in turn shorted itself to a trace on the board, just under that leg. Caused the amp to go into protect, but did not hurt anything. Check all your soldering very well.
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