Hello everyone. Been awhile since I have been here.
So purchased a used JL Audio 300/2 locally and was told it worked. Well it didn't. I opened it up and could clearly see that it had been worked on. The transistors on the heat sink were all missing their clips and were not even touching the heat sink. They were also missing the mica insulating strips that go between them and the heat sink. So what I did was I marked where the mounting holes for the mounting screws for the transistors on the heat sink and drilled holes. I then bought some mica strips and nylon screws and reapplied thermal paste and screwed them to the heat sink. Using a PC power supply I powered it on and it came on breifly then low ohm lite lit and PC power supply shut off. I had a speaker connected to it bridged and the music was distorted. So in my research it looks like it is possible bad transistors and is a common problem with these amps. Does this sound like it? Also I am having trouble finding a schematic with the circuit layout. All the threads I have seen are for either a 300/4 or 500/1. The transistors are the "IRF540". I have not had a chance to test yet, just running it by on here first to get an idea where to start at.
Thank you
So purchased a used JL Audio 300/2 locally and was told it worked. Well it didn't. I opened it up and could clearly see that it had been worked on. The transistors on the heat sink were all missing their clips and were not even touching the heat sink. They were also missing the mica insulating strips that go between them and the heat sink. So what I did was I marked where the mounting holes for the mounting screws for the transistors on the heat sink and drilled holes. I then bought some mica strips and nylon screws and reapplied thermal paste and screwed them to the heat sink. Using a PC power supply I powered it on and it came on breifly then low ohm lite lit and PC power supply shut off. I had a speaker connected to it bridged and the music was distorted. So in my research it looks like it is possible bad transistors and is a common problem with these amps. Does this sound like it? Also I am having trouble finding a schematic with the circuit layout. All the threads I have seen are for either a 300/4 or 500/1. The transistors are the "IRF540". I have not had a chance to test yet, just running it by on here first to get an idea where to start at.
Thank you
Thanks for the quick reply. I will take a look tomorrow when I have some time. Here is a pic of the internals. The first two transistors to the right looked like they may have been replaced. Where would a good source for heat sink clips be? I found these at digikey. Max Clip™ System Heat Sinks - Aavid Thermalloy | DigiKey
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Ok measured the transistors Q300 & Q301 on the source and drain. They both measure 2.2 ohms. These are the first two on the board on left hand side. I am thinking these are bad? They also have two different part numbers.
Now re her when I bought the amp it was already taken apart inside missing the heat sink clips like someone attempted to repair it. Are these even the correct transistors for this location?
Now re her when I bought the amp it was already taken apart inside missing the heat sink clips like someone attempted to repair it. Are these even the correct transistors for this location?
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Wow so whoever attempted to fix this amp before did not even use the correct transistors?
Is there anything else I should check?
I will order 2 x IRF540PBF
Thank you
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Not right now.
Clamp all transistors down tightly to the heatsink and insert a 10 or 15 amp fuse in the B+ line before applying power.
Clamp all transistors down tightly to the heatsink and insert a 10 or 15 amp fuse in the B+ line before applying power.
Getting ready to order 4 x IRF540PBF transistors and change out the channel. Since Newark Element 14 has the heat sink clips I was just going to order them from there. I usually order all my parts from Mouser. Is Newark a reputable dealer for transistors? All the reviews I have read online seem to be on the poor side.
Were the reviews from poor customer service? Their parts should be genuine.
Future is good to deal with and stock the clips.
Future is good to deal with and stock the clips.
Update time.
Still no luck. Replaced all 4 of the transistors. I put the heat sink clips on and at first the power supply was not come on. I checked the 12v and ground and I had continuity between them. So I I took the heat sink clips off and no more continuity and the amp powered on but powered right off again like was doing before. Not really sure where to go from here. I placed mica strips between the transistors and heat sink. I do not know why there is a connection between the 12v powered and the heat sink and ground. Could I still have a FET that is bad?
Still no luck. Replaced all 4 of the transistors. I put the heat sink clips on and at first the power supply was not come on. I checked the 12v and ground and I had continuity between them. So I I took the heat sink clips off and no more continuity and the amp powered on but powered right off again like was doing before. Not really sure where to go from here. I placed mica strips between the transistors and heat sink. I do not know why there is a connection between the 12v powered and the heat sink and ground. Could I still have a FET that is bad?
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I will try,
With the amp put back together with the heat sink clips on it will not power on at all. The power supply does not turn on. I then take the multi meter and have it set to continuity setting where it beeps. I put the positive lead in the 12v power wire connection and negative on the heat sink or touch the heat sink clips it beeps. If I remove the heat sink clips there is no beep. The amp powers on for a brief second and I get a flash from the low ohm led and then green power led turns off and power supply shuts off
With the amp put back together with the heat sink clips on it will not power on at all. The power supply does not turn on. I then take the multi meter and have it set to continuity setting where it beeps. I put the positive lead in the 12v power wire connection and negative on the heat sink or touch the heat sink clips it beeps. If I remove the heat sink clips there is no beep. The amp powers on for a brief second and I get a flash from the low ohm led and then green power led turns off and power supply shuts off
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Ok checking the transistors from D500 D501 which I take it as being the rectifier and then the Power transistors of Q500 to Q505 I will get a beep on the continuity check and then a ohm reading. If I take the leads of the multimeter and place them on the ground and 12v input I get a long beep and then I start reading an ohm reading. That will climb and then stop and go out. If I put a lead from the multimeter on the 12v input and then on the leg of the collector I get a short beep and a long continuous beep on the emitter on Q500 to Q505 and the emitter of D500 D501. I can then place lead over to the ground terminal and get coninuity on the emitter of Q500 to Q505 and Base and emitter of D500 D501. So is there a shot/possible ground? Because with the heat sink clips on the amplifier does not power on at all and the power supply shuts immediately off. Removing clips it power on for a second or so and then power supply shuts off.
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Don't use 'continuity'. Measure in ohms.
B+ terminal to connector should read 0 ohms.
B+ terminal to ground climbs because your meter is charging or discharging the capacitors.
B+ terminal to connector should read 0 ohms.
B+ terminal to ground climbs because your meter is charging or discharging the capacitors.
Checked the transistors on the power side. They read in the K ohm value but just continue to climb in value. I am at a loss. I am debating on just replacing all the transistors but don’t want to keep throwing money at this not knowing for sure what the issues could be. What I are the correct part numbers for the transistors on the power side? The ones on the board say “rfz44n 504g”
Thank you
Thank you
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