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Car audio amp trouble shoot for a noob
Car audio amp trouble shoot for a noob
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Old 16th February 2019, 02:07 PM   #1
Jstslamd is offline Jstslamd
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Default Car audio amp trouble shoot for a noob

Ok so Iíve had this amp sitting around for a while and I decided to open it up and see what the problem may be. Right off of the bat I noticed 4 blow resistors. Without hesitation I decided to order them up so that they can be replaced. After I calm down from thinking I solved the problem so easily I realized to myself that they blew for a reason. Why did they blow. After a little more digging I found a short in one of the icís. Does this sound like a cut and dry reason in why the resistors blew or should I keep digging and all of what I found is part of a bigger problem? Sorry if everything I said is a bit elementary but Iím quite new at this so any help would be more than appreciated. Iíve uploaded a picture of the amp and the parts in question. To add it looks like someone has been digging around in this amp quite a bit. Thanks again !
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Old 16th February 2019, 02:39 PM   #2
Jstslamd is offline Jstslamd
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For info purposes this a precision power a300.2
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Old 16th February 2019, 05:38 PM   #3
mnhiphop101 is offline mnhiphop101
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Do u have an oscilloscope? Without one it will be much more difficult to locate the problem.
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Old 16th February 2019, 08:57 PM   #4
Jstslamd is offline Jstslamd
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I do not.
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Old 16th February 2019, 08:59 PM   #5
Jstslamd is offline Jstslamd
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Are their cheap one oscilloscopes that are worth buying for a light diyer?
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Old 17th February 2019, 12:49 PM   #6
PapaZBill is offline PapaZBill  United States
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As long as you have a good VOM-Volt Ohm Meter, that will do.

There are good older oscilloscopes on Ebay or Amazon if you know what your looking for. HP,Tektronix among others but you will pay $150 to $300 for a good one.

There are a lot of handhelds and kits that you can purchase for $20, some of the better ones will cost as much as $150. The below link is an example. I don't have any experience with them, but for the price they should serve your purpose. Someone should be able to recommend a good handheld.

Handheld Oscilloscopes, DSO Nano V3: Amazon.com: Industrial & Scientific

Here is another example, If you don't want to build a kit I'm sure you can find one preassembled

Luxuglow DSO138 Digital Oscilloscope Kit Open Source 2.4" TFT 1Msps with Probe Handheld Pocket-Size DSO138 DIY Kit Electronic Diagnostic Tool: Amazon.com: Industrial & Scientific
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Last edited by PapaZBill; 17th February 2019 at 12:53 PM.
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Old 17th February 2019, 01:22 PM   #7
PapaZBill is offline PapaZBill  United States
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Are you referring to IC4 when you say you found a shorted IC?Idid t's not likely that a shorted IC alone did the damage to the Resistors.

The shorted IC and burned resistors may be due to shorted output transistors(Q10,Q11,Q12) and/or the drivers(Q22,Q23,Q24).

Remove the output transistors and drivers one at a time, and recheck the IC, and then the location of outputs and drivers.You may find one or several shorted transistors. It's also possible the IC is shorted.

Just one more thing, you may want to check out Perry Babins amp repair tutorial page Basic Car Audio Electronics
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Last edited by PapaZBill; 17th February 2019 at 01:25 PM.
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Old 17th February 2019, 01:30 PM   #8
PapaZBill is offline PapaZBill  United States
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One other thing. This amp uses bias pots and you will need to rotate all pots CCW before you power the amp up. I'm not familiar with this amps biasing adjustment, but someone here should be able to walk you through it.
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Old 17th February 2019, 05:33 PM   #9
Perry Babin is offline Perry Babin  United States
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The DSO138 is ONLY good for looking at audio signals. It's useless for switching PS or class D troubleshooting.

For $100, the Owon VDS1022I (<<<I is very important) is the best I've found but I wouldn't wish a cheap digital scope on my worst enemy. I have the owon and it has it's uses but as an only scope... NOT. It also needs a computer to work but most people have one laying around, even if it never gets used.

Find a good old analog scope with a CRT.
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Old 18th February 2019, 02:16 PM   #10
Jstslamd is offline Jstslamd
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Ok so the more I dig in this amp I’m starting to think I need to replace all of the midgets on the output side of the amp. My next hurdle will be finding a comparable or better option to replace them with. Unfortunately they don’t make the this specific transistor anymore. Could someone point me in the right direction ?
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