Hello!
I am working on this amp, it powers up and pulls 0.4amps. LED is lighting. Turning bias doesnt have an effect on idle current.
I have 33Volts DC on the speaker terminal.
Rail voltages are +- 38 VDC.
D7 was short.
I had positive Voltage on all preamp- opamps pin 4 which should be negative.
I changed both voltage regulators ( LM 337 and LM 317 ) , now its -30VDC on pin 4 and -2VDC on pin 8.
Has someone the schematics for this amp?
The board PC number is : PC-2034-D
Thank you very much in advance!
Best regards!
Andi
I am working on this amp, it powers up and pulls 0.4amps. LED is lighting. Turning bias doesnt have an effect on idle current.
I have 33Volts DC on the speaker terminal.
Rail voltages are +- 38 VDC.
D7 was short.
I had positive Voltage on all preamp- opamps pin 4 which should be negative.
I changed both voltage regulators ( LM 337 and LM 317 ) , now its -30VDC on pin 4 and -2VDC on pin 8.
Has someone the schematics for this amp?
The board PC number is : PC-2034-D
Thank you very much in advance!
Best regards!
Andi
Thank you very much!
from left to right
LM337
1: -35.8VDC
2: -36.8VDC
3: -31.5VDC
LM317
1: 1.36 VDC - goes slowly down
2: 2.56 VDC
3: 36.8 VDC
from left to right
LM337
1: -35.8VDC
2: -36.8VDC
3: -31.5VDC
LM317
1: 1.36 VDC - goes slowly down
2: 2.56 VDC
3: 36.8 VDC
Hi again!
I fixed the open traces and also found an open resistor but the amp will not power up properly.
After applying power it takes 2-3 seconds and the amp starts to pull 3 amps ( limited by my PS ) and every second it goes down to 0.4 amps and back to 3 amps with voltage drop.
Also the Power LED is blinking every second. And there is a " click " sound every second from one of the components, hard to locate.
Now i have 11 volts on pin8 of the opamps but still -23V on pin 4 of them.
Has somebody a hint what to check next?
THX in advance!
Best regards!
Andi
I fixed the open traces and also found an open resistor but the amp will not power up properly.
After applying power it takes 2-3 seconds and the amp starts to pull 3 amps ( limited by my PS ) and every second it goes down to 0.4 amps and back to 3 amps with voltage drop.
Also the Power LED is blinking every second. And there is a " click " sound every second from one of the components, hard to locate.
Now i have 11 volts on pin8 of the opamps but still -23V on pin 4 of them.
Has somebody a hint what to check next?
THX in advance!
Best regards!
Andi
DC voltage on all 3 terminals of the LM337?
Set the bias pots fully CCW. Does that allow the amp to power up?
What resistor was open?
Did you replace it?
Set the bias pots fully CCW. Does that allow the amp to power up?
What resistor was open?
Did you replace it?
bias pots were and are still fully ccw.
With that behavior i cant post voltages because all voltages go up and down every second also the rail voltages and the supply for the opamps
It was R181 , 62ohms and i replaced it .
Before i fixed the open trace the voltages were stable. ( cathode of D7 to ground )
With that behavior i cant post voltages because all voltages go up and down every second also the rail voltages and the supply for the opamps
It was R181 , 62ohms and i replaced it .
Before i fixed the open trace the voltages were stable. ( cathode of D7 to ground )
yes, its the same behavior then.
I dont want to blow something up and i did the test with 5 amps allowed. Also the same all the time.
I dont want to blow something up and i did the test with 5 amps allowed. Also the same all the time.
Are you seeing a pulse of DC on either of the bridging speaker terminals on the amp.
Check all of the 0.1 ohm source resistors to confirm that all are within tolerance.
Check all of the 0.1 ohm source resistors to confirm that all are within tolerance.
the speaker terminals pulse from 19 - 24VDC.
I also noticed when i give more amps the pulsing gets a little faster, from around 1Hz to 2Hz.
I desolder the Resistors and will report.
Thanks again!
I also noticed when i give more amps the pulsing gets a little faster, from around 1Hz to 2Hz.
I desolder the Resistors and will report.
Thanks again!
Hi!
I checked all source resistors, but i got readings from 0.8 to 0.12 ohms, i guess my probes are bad.
I decided to replace all source resistors but that had no positive effect.
I noticed when i remove LM337 , the pulsing stops, amp takes 0.4 amps but turning the bias pot has no effect and i still have dc on the speaker output.
So i replaced LM337 again but that also had no effect and the amp pulses.
Some hints are very welckome
I checked all source resistors, but i got readings from 0.8 to 0.12 ohms, i guess my probes are bad.
I decided to replace all source resistors but that had no positive effect.
I noticed when i remove LM337 , the pulsing stops, amp takes 0.4 amps but turning the bias pot has no effect and i still have dc on the speaker output.
So i replaced LM337 again but that also had no effect and the amp pulses.
Some hints are very welckome
Confirm that R26 and R28 are within tolerance.
If so, post the DC voltage on both terminals of each one (4 voltages).
Do have any DC voltage on either channel? Measure directly across the two terminals of each channel.
If so, post the DC voltage on both terminals of each one (4 voltages).
Do have any DC voltage on either channel? Measure directly across the two terminals of each channel.