(moved from from the solid state amplifier forum) I have a JBL 1201.1II class D monoblock car subwoofer amplifier I bought it off of ebay 'like new' but it came fried. They refunded my money (yay) and now I'd like to try my hand at fixing it. I am a complete novice, so I might need some baby talk... Symptoms: when hooked up to power, either 1. The 'power' led is off, and the 'protect' led is solid on, or 2. The 'power' led is solid on and the 'protect' led blinks fast (so fast it never appears to reach full brightness). Some components become very hot and start to smoke. No sound comes out at all. There are no apparent burn marks, though one side of the board has been apparently wiped clean with alcohol or something (looks new). The other side has a whitish residue all over it. Is this from blown electrolytic capacitors (mosfet), perhaps? The fuses are intact (though they could have been replaced). The plastic around where the fuses attach has been melted somewhat. From this information, does it sound like it is repairable? I have the service manual (with complete schematics)- pm me with an email if you want it. It is also available online with a quick google search. Where do I begin? Thanks
It sounds like there are shorted output transistors in the amp.
Email me if you want the service manual.
babin_perry@yahoo.com
Email me if you want the service manual.
babin_perry@yahoo.com
*googles output transistors for a while* I have the manual, but I don't know enough to tell which transistors are outputs. any obvious ways to tell that they are bad, or must they all be tested (and, apparently, removed)? How can I tell which transistors are the output transistors? I found a pic of a class A/B amp, and the output resistors were the two rows heatsinked to the case on either side of the pcb, on the side opposite the transformers. Here is a pic of my amp.
An externally hosted image should be here but it was not working when we last tested it.
the following is the class A/B pic with output transistors marked. are mine in the same positions? (large pic) (click for pic, because it is large)Thanks for the info! I checked them (in circuit...) and found one had an anomaly- a short. It is one of the IRF640N's (Q319 to be precise). I can order one and replace it... but I'm still curious. Does fixing the shorted transistor typically fix the issue (ie, protect circuit usually prevents further damage), or is there often another problem? Anything else common I should check out?
Cut the shorted one out, clamp ALL heatsink mounted components tightly to the heatsink and power the amp up with a single 15 or 20 amp fuse. If the amp plays normally, at low levels and doesn't blow the fuse (20A max), you may only have to replace the output FETs in that group. At the very least, you need to replace all of the 640s in parallel with the one that failed but I'd suggest that you replace all in the output group (640s and 9640s) with the one that failed.
OK, I cut out the transistor, and hooked up all the heatsinks like they are during normal use. Instead of hooking it up with a small fuse, I hooked it up to a variable dc power supply (12v @ about 2 amps). The protect light is off, and the power light became solid on. I hooked up audio input and sound comes out clear, and the gains and everything else seem to work perfectly (and did not overamp the power supply). I will order replacement transistors soon. Is that enough to tell that it is working fine, or should I hook it up in a vehicle and try it at 10 amps or so? Thank you very much for your help. Yesterday I didn't even have a clue, and today I have an amp!
ok. I tried it again under about 10-15 amps, and everything worked smoothly for a few minutes, so I'm confident now that everything will be peachy. I checked that gate resistor (and the others for good measure) and they all check out.
One more question, though, to be sure I'm understanding you. Does "output group" mean basically everything under that same heatsink clamp thing? Or do I need to replace all of the 640's and 9640's, including the ones on the opposite side (a total of 18 transistors)?
One more question, though, to be sure I'm understanding you. Does "output group" mean basically everything under that same heatsink clamp thing? Or do I need to replace all of the 640's and 9640's, including the ones on the opposite side (a total of 18 transistors)?
Well, I seem to have hit another snag. Where can I get the transistors? I need IRF9640 and IRF640N transistors.
I've seen several sites selling them, but apparently there are a lot of "fakes" out there, and I have no idea how to avoid them. There are also a lot with extra letters and numbers, and I don't know what any of it means.
This page at avnet, for example.
At Fry's, they have the brand NEC, but I don't know how to judge equivalent parts. I jotted down what they have that looked similar. I can post the numbers if that helps.
edit: Is digikey good? I found IRF9640's and IRF640N's on the site, but they are not stock items, and min quantities are in the hundreds. They do have PBF versions (which I linked to). Does that only mean lead-free? So would they be fine? I'd still like to know the NEC equivs, or what I need to know to find one. They have books, but I don't know what is and is not important.
I've seen several sites selling them, but apparently there are a lot of "fakes" out there, and I have no idea how to avoid them. There are also a lot with extra letters and numbers, and I don't know what any of it means.
This page at avnet, for example.
At Fry's, they have the brand NEC, but I don't know how to judge equivalent parts. I jotted down what they have that looked similar. I can post the numbers if that helps.
edit: Is digikey good? I found IRF9640's and IRF640N's on the site, but they are not stock items, and min quantities are in the hundreds. They do have PBF versions (which I linked to). Does that only mean lead-free? So would they be fine? I'd still like to know the NEC equivs, or what I need to know to find one. They have books, but I don't know what is and is not important.
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also, look at tayda electronics. i have used them before for something that seemed hard to get, and they had it in international rectifier (brand) st mocro, and fairchild are decent brands, too. tip: when you order, order 10+ for more reliability, since you will get them all from the same batch. the extra numbers on the transistor below the part number, next to the symbol in ir's is the build date and line
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