I have a strange issue with theis amp..
If i install the audio driverboards amp will not power up no power light no nothing its dead..
If i take both of the audio driverboards out of the amp amp will power up and idle perfectly ..
I checked all regulated voltages and all are there and correct..
I get rail voltages also..
But with the audio driverboards in i get nothing..
Any ideas what might cause this or what to check??
If i install the audio driverboards amp will not power up no power light no nothing its dead..
If i take both of the audio driverboards out of the amp amp will power up and idle perfectly ..
I checked all regulated voltages and all are there and correct..
I get rail voltages also..
But with the audio driverboards in i get nothing..
Any ideas what might cause this or what to check??
voltage on the KA7500 with no audio driverboards in the amp..
Pin 1:0.00
Pin 2:0.00
Pin 3:0.00
Pin 4:0.00
Pin 5:0.00
Pin 6:3.80
Pin 7:0.00
Pin 8:13.80
Pin 9:5.33
Pin 10:0.00
Pin 11:13.80
Pin 12:13.80
Pin 13:4.95
Pin 14:4.95
Pin 15:4.95
Pin 16:0.00
with them in
Pin 1:6.32
Pin 2:0.00
Pin 3:0.00
Pin 4:0.00
Pin 5:0.00
Pin 6:0.00
Pin 7:0.00
Pin 8:13.22
Pin 9:0.00
Pin 10:0.00
Pin 11:13.22
Pin 12:13.22
Pin 13:4.95
Pin 14:4.95
Pin 15:4.95
Pin 16:0.00
LM393 with boards in the amp
Pin 1:6.91
Pin 2:0.01
Pin 3: starts at 6.00 and slowly drops down to 5.00
Pin 4:0.00
Pin 5:1.03
Pin 6:3.25
Pin 7:0.10
Pin 8:0.06
With the audio driverboards removed
LM393
Pin 1:0.10
Pin 2:0.00
Pin 3:0.29
Pin 4:0.00
Pin 5:1.02
Pin 6:3.32
Pin 7:0.11
Pin 8:13.22
I tryed installing 1 driverboard at a time in either location amp does the same thing
Pin 1:0.00
Pin 2:0.00
Pin 3:0.00
Pin 4:0.00
Pin 5:0.00
Pin 6:3.80
Pin 7:0.00
Pin 8:13.80
Pin 9:5.33
Pin 10:0.00
Pin 11:13.80
Pin 12:13.80
Pin 13:4.95
Pin 14:4.95
Pin 15:4.95
Pin 16:0.00
with them in
Pin 1:6.32
Pin 2:0.00
Pin 3:0.00
Pin 4:0.00
Pin 5:0.00
Pin 6:0.00
Pin 7:0.00
Pin 8:13.22
Pin 9:0.00
Pin 10:0.00
Pin 11:13.22
Pin 12:13.22
Pin 13:4.95
Pin 14:4.95
Pin 15:4.95
Pin 16:0.00
LM393 with boards in the amp
Pin 1:6.91
Pin 2:0.01
Pin 3: starts at 6.00 and slowly drops down to 5.00
Pin 4:0.00
Pin 5:1.03
Pin 6:3.25
Pin 7:0.10
Pin 8:0.06
With the audio driverboards removed
LM393
Pin 1:0.10
Pin 2:0.00
Pin 3:0.29
Pin 4:0.00
Pin 5:1.02
Pin 6:3.32
Pin 7:0.11
Pin 8:13.22
I tryed installing 1 driverboard at a time in either location amp does the same thing
Last edited:
There are too many pins with 0.00v. Various problems:
Pin 5 should be at approximately 1.6v. The IC wouldn't produce any pulses that could be considered normal with that pin at 0v.
Pin 2 should likely be near 2.5v. At 0v, the comparator (internal to the IC) can't function.
Pins 9 and 10 are generally the same voltage (±0.05v)
When it was idling perfectly, did you confirm that all FETs were being driven?
Pin 5 should be at approximately 1.6v. The IC wouldn't produce any pulses that could be considered normal with that pin at 0v.
Pin 2 should likely be near 2.5v. At 0v, the comparator (internal to the IC) can't function.
Pins 9 and 10 are generally the same voltage (±0.05v)
When it was idling perfectly, did you confirm that all FETs were being driven?
Ok with the audio driverboards out of the amp .. and the amp powerd up..
I get nice square waves on all of the gate legs of all power supply fets..
KA7500
Pin 1:0.01
Pin 2:2.41
Pin 3:0.08
Pin 4:0.00
Pin 5:1.46
Pin 6:3.70
Pin 7:0.00
Pin 8:13.02
Pin 9:5.34
Pin 10:5.34
Pin 11:13.08
Pin 12:13.08
Pin 13:4.96
Pin 14:4.96
Pin 15:4.96
Pin 16:0.00
LM393
Pin 1:0.10
Pin 2:2.49
Pin 3:0.30
Pin 4:0.00
Pin 5:1.03
Pin 6:3.23
Pin 7:0.10
Pin 8:13.06
This is with no audio driverboards in the amp..
Do the voltages appear to be correct or do i have a problem somewhere?
I guess i wasent making good contact with the pins on the first attempt
I get nice square waves on all of the gate legs of all power supply fets..
KA7500
Pin 1:0.01
Pin 2:2.41
Pin 3:0.08
Pin 4:0.00
Pin 5:1.46
Pin 6:3.70
Pin 7:0.00
Pin 8:13.02
Pin 9:5.34
Pin 10:5.34
Pin 11:13.08
Pin 12:13.08
Pin 13:4.96
Pin 14:4.96
Pin 15:4.96
Pin 16:0.00
LM393
Pin 1:0.10
Pin 2:2.49
Pin 3:0.30
Pin 4:0.00
Pin 5:1.03
Pin 6:3.23
Pin 7:0.10
Pin 8:13.06
This is with no audio driverboards in the amp..
Do the voltages appear to be correct or do i have a problem somewhere?
I guess i wasent making good contact with the pins on the first attempt
KA7500
Pin 1:6.30
Pin 2:2.54
Pin 3:4.74
Pin 4:3.96
Pin 5:1.56
Pin 6:3.66
Pin 7:0.00
Pin 8:13.22
Pin 9:0.00
Pin 10:0.00
Pin 11:13.22
Pin 12:13.22
Pin 13:4.95
Pin 14:4.95
Pin 15:4.95
Pin 16:0.00
LM393
Pin 1:6.91
Pin 2:2.48
Pin 3:starts out at 6.80 and keeps falling down towards 0.00
Pin 4:0.00
Pin 5:1.02
Pin 6:3.40
Pin 7:0.10
Pin 8:13.22
Pin 1:6.30
Pin 2:2.54
Pin 3:4.74
Pin 4:3.96
Pin 5:1.56
Pin 6:3.66
Pin 7:0.00
Pin 8:13.22
Pin 9:0.00
Pin 10:0.00
Pin 11:13.22
Pin 12:13.22
Pin 13:4.95
Pin 14:4.95
Pin 15:4.95
Pin 16:0.00
LM393
Pin 1:6.91
Pin 2:2.48
Pin 3:starts out at 6.80 and keeps falling down towards 0.00
Pin 4:0.00
Pin 5:1.02
Pin 6:3.40
Pin 7:0.10
Pin 8:13.22
When the voltage on pin 3 is above the voltage on pin 2, pin 1 should be near the positive supply voltage.
When the voltage on pin 3 is below the voltage on pin 2, the voltage on pin 1 should be near ground.
When pin 1 on the 293 is near ground, pin 1 on the 494/7500 should be near ground and the IC should produce output.
When the voltage on pin 3 is below the voltage on pin 2, the voltage on pin 1 should be near ground.
When pin 1 on the 293 is near ground, pin 1 on the 494/7500 should be near ground and the IC should produce output.
ok i resolerd the power supply driverboard to the main board
Heres what i get on the 393 now
Pin 1:6.91
Pin 2:2.48
pin 3:starts out at 3.00 then drops to 2.59 volts then spikes back up to 2.70 volts and continues to do this ..
Pin 4:0.00
Pin 5:1.02
Pin 6:3.37
Pin 7:0.10
Pin 8:13.22
Voltage on PIN 1 of the 7500 remains at 6.91 volts..
Heres what i get on the 393 now
Pin 1:6.91
Pin 2:2.48
pin 3:starts out at 3.00 then drops to 2.59 volts then spikes back up to 2.70 volts and continues to do this ..
Pin 4:0.00
Pin 5:1.02
Pin 6:3.37
Pin 7:0.10
Pin 8:13.22
Voltage on PIN 1 of the 7500 remains at 6.91 volts..
It may be too fast for a multimeter to catch it. Use your scope. Set the vertical amp to 5v/div and set the coupling to DC. Align the trace to the reference. Set the timebase so that the trace turns to a slow moving dot and watch the voltage on pin of the 7500 closely. You should see it pulse at the point where the voltage on pin 3 of the 293 jumps back up.
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