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knil7777 2nd November 2012 11:07 PM

Equivalent Transistors for JL 500/1
I have been working on the above amp and I have found some of the driver transistors around the main audio channel that are defective. I can't seem to find the A1070 or the C3207 transistors. I searched a few thread and saw where the KSA1220A might work for the A1070, would the KSC2690A be a good replacement for the C3207? It looks like the voltages are lower than the original parts for both transistors. I am assuming the KSC2690A would be a good match since it is the NPN counterpart to the KSA1220A.

Perry Babin 2nd November 2012 11:08 PM

The voltage in the amp is never going to be more than about 90v. 160v transistors are easily good enough.

knil7777 2nd November 2012 11:15 PM

Thanks Perry, I will order the KSC2690A and the KSC1220A, would you recommend that I replace both sets of the original A1070 and C3207 with these new parts. It looks like the pre-drivers on the right side of the audio transistors are good but since this is a mono amp and all 4 audio transistors are the IRF540, I was thinking that replacing all of the old A1070's and C3207's might be a good idea to keep consistent parts in the pre-driver section even though the ones on the right side of the Audio Transistiors don't seem to be parallel parts with the bad ones on the right side of the Audio Transistors.


Perry Babin 2nd November 2012 11:45 PM

I don't generally recommend replacing components that are intact unless there is a good reason. The original parts are not unreliable so I'd leave them.

The 3906s are paralleled. None of the other drivers are paralleled.

knil7777 13th November 2012 02:23 AM

Okay, I got the parts in and this one is still acting strange. The power supply is not showing a nice square wave and one of the main audio transistors is getting real hot. Powering through my headlamp, it pulses the lamp as it tries to power up. The PNP pre driver transistor on one side of the audio transistors is showing .134 volts in diode mode on its outer legs no mater which way I have the probs posistioned. The one on the other side of the audio transistors s showing .543 volts with probes one way and OL with them swapped. Not sure where to go from here. May take picks of what o-Scope is showing when I go back in. The wife was getting up set with me spending so much time in my workshop, I had to call it for a few hours while I regroup.

Perry Babin 13th November 2012 05:10 AM

Remove the rectifier (D600). Do you get a clean square wave on all PS FETs?

Do they all remain cool for at least a minute?

knil7777 13th November 2012 01:27 PM

I will remove the rectifier when I get home, I was thinking it must be in the power supply section since the square wave was looking so bad, not sure if something bad in the audio section could be causing the power supply to react this way but removing the rectifier should help isolate the problem.

Perry Babin 13th November 2012 03:52 PM

The power supply waveforms for amps with regulation for the rail voltage don't generally look clean and square at idle.

knil7777 14th November 2012 12:40 AM

3 Attachment(s)
Well, i was able to get home before and work on the JL Audio amp again. The power supply waveform looked almost perfect with the rectifier out of teh amp. I soldered it back in a took a picture of what the waveform looks like while it is attempting to power the audio section. I also took a pic of 60 Hz sin wave that I was playing through the head unit. The one pic is of the output waveform with no audio and the last pic is of the distorted sin wave. I did a bit more trouble shooting and found some bad resistors near the old 3906's in the pre driver section that I was able to replace with very similar value test parts (using through hole resistors temporary since the original are surface mount componets that I will need to order, but I was wanting to wait until I had a good handle on what other parts this amp may be needing). Does anyone have any idea what may be causing this do you think that using the KSC2690A and KSA1220A to replace the A1070 or the C3207 may be part of the problem. I almost wonder if I got these soldered in wrong (NPN in place of the PNP) I took my time, but it was late at night and I wouldn't put anything past my lack of sleep causing me to rush and make that kind of mistake. Hopefully the waveforms will help diagonose the problem. THanks,

Perry Babin 14th November 2012 12:45 AM

For every scope photo that you post, you must post the vertical amplifier and timebase settings as well as the terminal that you had the probe on. In most instances, it's best to post a single photo with all of the relevant information in each post.

There is nothing wrong with the power supply waveform as far as I can tell.

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