zapco ag 350

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Change the fuse to a 10 amp fuse (added protection in case something goes wrong). Leave the transistors clamped to the sink. If you've already removed the clamps, replace them.

Look up the datasheet for the power supply driver IC (SG3525) so you can see how the pins are numbered.

Connect the black meter lead to the ground terminal of the amplifier. Set your meter to DC volts. Power up the amp (including remote) and measure the voltage on each of the pins of the SG3525. Don't slip and short between pins

Post the voltages like this (copy and paste this):

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
 
What's the DC voltage on the second and third legs of the 2n6714 transistor (Q30) near the IC? If the third leg has ~12v but the middle leg has ~0v, check the diode DZ5 to see if it's shorted.

If there is no voltage on the transistor... There are 2 diodes near the FETs. Do they have ~12v on both sides?

If not, there are 2 10 ohm resistors next to the diodes. Do they have more than a volt across them? If so, remove power from the amp and measure the resistance across them.
 
zapco

I did some voltage checks to 2n6714 no voltage on second leg but 13 volts on third leg voltage on zener diodes has voltage on 1 side only.but when i tested i forgot to hook up remote wire to amp and when i did i rechecked voltage on 2n6714 and there was less than 1 volt on it second leg and third leg
 
It sounds like there is either excessive current flow through the transistor (would likely be causing transistor to overheat) or there is excessive resistance in the circuit feeding the transistor.

With the amp powered up (including remote), measure the voltage on the center leg of the FETs. If it's near 12v, measure the voltage on each side of the 10 ohm resistors.
 
If those were measured with the remote applied, it seems like D6 and D7 are open. Or, there could be a weak trace between D6/7 and the third leg of the transistor.

Measure the voltage on the striped side of D6/7 with remote applied. If they have ~12v, the trace is likely open. This could be due to leaking electrolyte from the large filter capacitors.
 
The FETs are likely OK.

If the capacitors leaked, the electrolyte could have damaged the trace.

You could try running a jumper from the striped side of D6/7 to the third leg of the transistor to see if the amp will power up normally. If you do this, the jumper should be fused with a 1 amp fuse and you should have a 10 amp fuse as the main power fuse in the amp.

If the amp powers up and operates properly, you would need to disassemble the amp, remove the flter caps, clean up the corrosion and replace the capacitors (with new caps, don't reinstall the old caps).
 
zapco

i am guessing that the bigger caps are the filter caps this amp has 6 big caps what are the 4 taller ones for? the 2 closest to d6 and d7 is what you are referring too right c24 and c40 i hope.do you want me to run a jumper from d6 and d7 to third leg of transistor 2n6714?
 
Correct, the trace that connects Q30 to D6 and D7 passes under the two filter caps nearest to the diodes. These are the ones you need to remove.

You need to use a fused jumper (very important). A standard inline fuse holder with a 1 amp fuse may be long enough to reach between the diodes and Q30. Don't jump it without a fuse.
 
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