I have a JL 300/4 (v1 I believe) that had an issue. It had no output on the front right output. Other 3 channels worked just fine. All 3 LED's on all 4 driver boards lit up green. The only thing that looked abnormally hot under a thermal camera to me was Q510. I have seen it mentioned in other threads as a potential problem, but what is the purpose of this particular IRFZ44N?
After a bunch of other checks and looking through a couple other threads on this amp and after cleaning and reseating the predriver board, all the channels worked. So I'm going assume that this was the only issue. This was my first time repairing one of the old slash amps, so I was not really sure what to expect. I did go through and resolder the 47k larger resistors on all the driver boards like some people had found to be problematic. I also reset the bias of all channels to 4mV (they were all close already between 3.5 and 4.5mV to begin with). The amp idles at about 2.2amps on 13.4V supply, which seems kinda high but I have no reason to think it is wrong. A bunch of the discrete transistors on the drive cards get up around 80C also, but seeing how they were ALL doing that and I had good sound/voltages, I assume that is just normal. Do all of these things sound correct on these older JL's?
After a bunch of other checks and looking through a couple other threads on this amp and after cleaning and reseating the predriver board, all the channels worked. So I'm going assume that this was the only issue. This was my first time repairing one of the old slash amps, so I was not really sure what to expect. I did go through and resolder the 47k larger resistors on all the driver boards like some people had found to be problematic. I also reset the bias of all channels to 4mV (they were all close already between 3.5 and 4.5mV to begin with). The amp idles at about 2.2amps on 13.4V supply, which seems kinda high but I have no reason to think it is wrong. A bunch of the discrete transistors on the drive cards get up around 80C also, but seeing how they were ALL doing that and I had good sound/voltages, I assume that is just normal. Do all of these things sound correct on these older JL's?
Q510 is what drives the flyback/low-voltage transformer.
The rest seems normal. I don't set the bias that high but there's nothing wrong with it.
The rest seems normal. I don't set the bias that high but there's nothing wrong with it.