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Old 7th May 2008, 10:53 PM   #1
shagone is offline shagone  United States
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Default jl 300/4 driver card diodes?

I have a jl 300/4 here with one channel out. i replaced the outputs and one bad 10 ohm resistor on the driver board. there is a smt zener diode that is shorted that i need to replace on the driver board. i need the value of it or an acceptable replacement part number or marking value. the diode looks like it says 6.8Y on it. this diode is mentioned in Perry's tutorial but the value was not given.
Thanks in advance.
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Old 7th May 2008, 11:10 PM   #2
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I used 6.8v zeners on the few I've seen. If you can get to the card next to it, measure the voltage across the same component on it.
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Old 12th May 2008, 09:35 PM   #3
shagone is offline shagone  United States
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Quote:
Originally posted by Perry Babin
I used 6.8v zeners on the few I've seen. If you can get to the card next to it, measure the voltage across the same component on it.

I still need to measure the voltage but is there any chance that a 5.6v zener will work? i have these readily available but i would need to order 6.8v zeners.
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Old 12th May 2008, 10:28 PM   #4
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The 5.6 may work well enough to allow you to get it up and running but I'd recommend ordering the correct parts before you put it back into service.

If the amp doesn't work properly with the 5.6, order and install the 6.8 before you do anything else. If it works well with the 5.6, you can be relatively sure that there are no more defective components.
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Old 4th June 2008, 01:24 AM   #5
shagone is offline shagone  United States
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i ordered the correct 6.8v zener and installed it. now i have 28v dc on the output of one channel. what would cause that? i can't find a short but i could be missing something?
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Old 4th June 2008, 04:47 AM   #6
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Is the problem for the same channel that you changed the zener in?
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Old 4th June 2008, 09:12 PM   #7
shagone is offline shagone  United States
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same side (rear) but i think it is the other channel. and i get no sound out of the channel that i put the zener in but no dc offset.

i may just give this one back to the owner because i have spent too long on it unless there is a reletively simple solution.

i'm getting about 2.5 amps of idle current without a limiting resistor and no protection lights.
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Old 4th June 2008, 11:32 PM   #8
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Do you have any open resistors near the output transistors you replaced?

You need to use your meter to determine if the channel with DC is the same as the one with the shorted Zener. Measure the resistance from the gates of the channel with DC to the driver board pins. There are resistors in series so it's better to go from the driver board side of the gate resistor. From there to the driver board, you should read 0 ohms.

Can you confirm that you have signal at the input of the driver board for the defective channels? I don't know which pins are audio input. You may have to check the working channels to determine which are the input pins.

If you have one or more pairs of output transistors getting hot, the bias may be set a bit too high.
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Old 5th June 2008, 02:15 AM   #9
shagone is offline shagone  United States
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there are no bad resistors near the outputs i changed but one pair is getting hotter than the rest. i never changed the bias but i did change the outputs in that channel. i'll try to adjust it.

would that cause that much dc offest?
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Old 7th June 2008, 12:40 AM   #10
shagone is offline shagone  United States
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does anyone know if JL has a flat rate amp repair service or what they charge so i know when i'm getting in over my head?
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