Ok so I’ve 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 ic’s. 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 I’m quite new at this so any help would be more than appreciated. I’ve 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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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
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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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
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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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.
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.
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 ?
You should check them before blindly replacing them.
Speaker Load and Amplifier Failure
Are you referring to the BDT81/82?
2N6488 and 2N6491
Speaker Load and Amplifier Failure
Are you referring to the BDT81/82?
2N6488 and 2N6491
Ok so I took some readings on the fets on the power supply and the bjt’s. As for the fets they all measured out the same and had a good reading at.444. Only reason I was considering putting new fets in was because it looks as though they have been replaced at one point and if I was going to fresehen up the rest of the amp why not them as well. On to the bjt. They all seem to read the same. Q1-3 bdt82 measure .45 on the base .35 on the collector. Q4-6 bdt81 measure .47 on the base and .35 on the emitter. Q7-9 .45 on the base .35 on the collector. Q10-12 so and open. Sorry for the long drawn out post. I’m just trying to convey my findings. Hope I’m on the right path. I appreciate everyone’s help!
Each transistor has to be checked like this, leg numbering vs probes:
1-2
1-3
2-3
This has to be done with the probes with one polarity then reversed. The first test is done on diode-check. To check for leakage, the tests need to be re-done with the meter set to ohms. This sounds like a lot of testing but it takes only a few seconds for each transistor.
Any transistor that reads significantly different than the others with the same part number are suspect.
This needs to be done with the transistors out of the circuit.
1-2
1-3
2-3
This has to be done with the probes with one polarity then reversed. The first test is done on diode-check. To check for leakage, the tests need to be re-done with the meter set to ohms. This sounds like a lot of testing but it takes only a few seconds for each transistor.
Any transistor that reads significantly different than the others with the same part number are suspect.
This needs to be done with the transistors out of the circuit.
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