Hi guys someone that can help me with a Planet audio AC1500.1 amp turn on but no sound. the channel just pop out the subwoofer and give me +27vdc on the speaker channel. I already opened the amp looking for bad transistors but both mosfet and output transistors tested good not sure what is causing this problem any help is aprecciated.
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Do you have positive and negative rail voltage?
Do you have positive and negative regulated voltage on the power supply pins of the op-amps?
Do you have positive and negative regulated voltage on the power supply pins of the op-amps?
I have +-27 vdc on both rails and 12.4 v on the 12 pin of the TL494cn also 30v on the middle leg of the output transistors
The op-amps are U1 and U2 in the preamp section.
Q111 should have negative rail voltage on the center leg.
Q110 should have positive rail voltage on the center leg.
Q111 should have negative rail voltage on the center leg.
Q110 should have positive rail voltage on the center leg.
Q110=30vdc
Q111=-30vdc
U1 PIN4= -15.6VDC
PIN8=15.1 VDC
U2 PIN4=15.6VDC
PIN8=15.1VDC
U6 PIN4=0V
PIN8=12.3VDC
Q111=-30vdc
U1 PIN4= -15.6VDC
PIN8=15.1 VDC
U2 PIN4=15.6VDC
PIN8=15.1VDC
U6 PIN4=0V
PIN8=12.3VDC
I'm assuming that "U2 PIN4=15.6VDC" is a typo.
Reinstall the outputs and remove Q105 and Q106. Do you still have 20v+ offset?
What are the part numbers on Q105/6?
Reinstall the outputs and remove Q105 and Q106. Do you still have 20v+ offset?
What are the part numbers on Q105/6?
Hi perry yes it's -15.6 vcd I already reinstalled the outputs the voltages I give to you are with outputs in board. How ever I noticed that u2 was installated pointing to the up and the U1 down not sure if this is tje correct way they need to be! I mean with the serial number On u2 is inversed pointed up
The opamps are installed correctly in the amp
1 is supposed to face the opposite direction according to the screen print on the board
1 is supposed to face the opposite direction according to the screen print on the board
When you measured the voltage, did you use the actual pin numbering for the op-amp as a guide or did you use the silkscreen?
I used the datasheet for actual pin numbers. There's a bad reading at some point? I was wrong 'bout U2 it's in the correct orientation the board prints are correct. And the voltages i measure too.
All op-amps are generally oriented in the same way but the silkscreen does show pin 1 in the pad with the square in the silkscreen.
Did you remove Q105/106 and check for DC voltage across the speaker terminals?
Did you remove Q105/106 and check for DC voltage across the speaker terminals?
Thanks for the clarification. I'll take the transistors this evening today and give you an update.
OK I already remove the drivers the offset voltage is gone.both transistors seem to be bad.
Drivers part numbers are:
A1023
C1027
This Components are hard to get as I can see!
Drivers part numbers are:
A1023
C1027
This Components are hard to get as I can see!
Last edited:
Did you check them to confirm that they were defective?
The problem could be a stage before this one.
The problem could be a stage before this one.
Ok I cheched them again and this what I get Then I assume both drivers are working right if I'm not wrong. My bad here
A1023 PNP transistor
B-C =.690
B-E =.695
C-E = OL
Inversed all OL
C1027 NPN Transistor
B-C =.693
B-E =.696
C-E = OL
Inversed all OL
A1023 PNP transistor
B-C =.690
B-E =.695
C-E = OL
Inversed all OL
C1027 NPN Transistor
B-C =.693
B-E =.696
C-E = OL
Inversed all OL