After reading some threads on here I went through and replaced all of the TO-220 type components on the main board that contact the heat sink in an attempt to fix my problem,... it didn't fix everything. I have sound from all channels now except for the front left channel. I've switched the inputs all around and the problem stays with the front left channel output of the amp. I tested the amp on the bench using the same test speaker for all channels so I know it's not the speaker either. Where else should I be looking? What other components should I look at replacing?http://files.diyaudio.com/forums/images/smilies/confused.gif
Any help would be greatly appreciated.
Any help would be greatly appreciated.
I haven't checked any internal LED's. The power LED is the only one of the three illuminated on the front. Are there internal LED's to look for?
I think I have the same problem on my 300/4... Did your power supply IRF540 got really hot when on idle? (the one that's not heatsinked next to the toroids and power supply controller... I have my own thread but I'm looking for answers everywhere 😕
There is a large resistor next to the LEDs marked 473. Add new solder to both pads, desolder the pads and then re-solder it. Does that help?
All of these resistors on all of the driver boards need to have this done to their terminals. This is the most common failure in these amps.
All of these resistors on all of the driver boards need to have this done to their terminals. This is the most common failure in these amps.
I have the exact same problem, 2 of the top leds are not lighting up. I re-soldered the 473 resistor and no success..
However, I did notice a difference in the voltage reference to ground on the 2 differential amplifier transistors that you mentioned in my post.. Those read 2G X can't seem to get anything on the internet..
However, I did notice a difference in the voltage reference to ground on the 2 differential amplifier transistors that you mentioned in my post.. Those read 2G X can't seem to get anything on the internet..
I resoldered the 473 resistor as you mentioned on all 4 boards. When I apply power, all three light come on on the other three boards, but still only the one on the other board. After about a second, the two lights come on then go right back off and stay off. I don't know if it was doing this before , but it's something I just noticed that may help in the diagnosis.
I removed the little "B" transistor and all the lights are now ON
http://www.bcae1.com/temp/jlaudioboardx.jpg
According to Perry these are BC850C's
I'm a little afraid of keeping the amp ON but the lights on top don't flicker or anything, they just stay ON.
It's crazy how a super tiny little critter can do such a mess!! my supply voltage, even with the amp OFF (but with the leads conected) was oscilating... Now it's not...
http://www.bcae1.com/temp/jlaudioboardx.jpg
According to Perry these are BC850C's
I'm a little afraid of keeping the amp ON but the lights on top don't flicker or anything, they just stay ON.
It's crazy how a super tiny little critter can do such a mess!! my supply voltage, even with the amp OFF (but with the leads conected) was oscilating... Now it's not...
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Perry,
I really appreciate your help thus far. I'm apprehensive about just removing a component as sameoldme described. Those parts are there for a reason. Can you give me any other direction or identify what the SOT-23 transistors are on these boards.
I really appreciate your help thus far. I'm apprehensive about just removing a component as sameoldme described. Those parts are there for a reason. Can you give me any other direction or identify what the SOT-23 transistors are on these boards.
I'm sorry Perry... I though we were on to something here..
BTW: I just didn't removed the transistor, I tested it and compared to the other 3 boards and that was the only one that didn't have "Zero" volts at the emitter when at idle... that's why I removed it.
I resoldered all of the circled resistors in the picture as well as the transistors and I still get the same thining. Is there something else I can try to isolate the problem, maybe change to bad board with one of the good ones to see if the problem is on the input side of the board?
Measure the DC voltage directly across each of the two LEDs that won't remain lit. Post the voltage for each.
When you soldered the resistors, did you add new solder, remove all solder (or as much as possible) and then resolder the resistors?
Perry,
I was going back over the board and not only resoldering the joints, but also measuring the resistance of each resistor. I found two resistors that aren't measuring what they should. In the picture with all of the components circled, there are two 10ohm resistors in the lower left hand corner. the inner most resistors measures correctly, the outer resistor measures 1.5 meg-ohm, and the 47kohm resistor on that same side of the board measures 1.2 meg. While these are obviously out of spec by what should be there, do you think it could be the problem?
I was going back over the board and not only resoldering the joints, but also measuring the resistance of each resistor. I found two resistors that aren't measuring what they should. In the picture with all of the components circled, there are two 10ohm resistors in the lower left hand corner. the inner most resistors measures correctly, the outer resistor measures 1.5 meg-ohm, and the 47kohm resistor on that same side of the board measures 1.2 meg. While these are obviously out of spec by what should be there, do you think it could be the problem?
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