Hi,
I have this amplifier and it has no power. There is no output voltage from the transformer (no +-66V), thus I think that it is something in the power supply. Does anyone have the circuit diagram for this amplifier please?
Thanks
I have this amplifier and it has no power. There is no output voltage from the transformer (no +-66V), thus I think that it is something in the power supply. Does anyone have the circuit diagram for this amplifier please?
Thanks
Post the DC voltage on all terminals of the TL494 driver IC. Copy and paste the following list and fill in the blanks.
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:
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:
Thanks for your reply. I will check all the voltages tomorrow, however yesterday I noted that there is no voltage on pin 12 of the TL494. I tried to follow the track of the supply of the IC, and I noticed that there is a transistor (close to 2 diodes) that has 12V on the base and emitter (If I am not mistaken) but the collector has no voltage on it. I checked the transistor with the DMM on diode check and I noticed that it is not faulty.
Hi,
Sorry my mistake. I just noticed that the remote wire was cut and that is why the amplifier was not powering on. Still the amplifier has no audio out (there was a short on one of the output speakers, in fact the connector has melted). I disconnected the AD2K module and noticed that there is a transistor (part number 2D) that is giving 0.68V between Base and Collector and 1.46V between Base and Emitter. Probably the fault of no output is coming from there. Do you agree? I will try to find an equivalent and replace and will reply back. In the mean time if you have any hints on this fault, please contact me via this forum. Thanks and happy festive season.
Sorry my mistake. I just noticed that the remote wire was cut and that is why the amplifier was not powering on. Still the amplifier has no audio out (there was a short on one of the output speakers, in fact the connector has melted). I disconnected the AD2K module and noticed that there is a transistor (part number 2D) that is giving 0.68V between Base and Collector and 1.46V between Base and Emitter. Probably the fault of no output is coming from there. Do you agree? I will try to find an equivalent and replace and will reply back. In the mean time if you have any hints on this fault, please contact me via this forum. Thanks and happy festive season.
I see nothing about voltage on pin 12 in the post before mine.
If the transistor is reading 1.46v on diode-check between B and E, it's likely defective.
I don't have a diagram for the module but I think someone posted one on the forum some time ago.
If the transistor is reading 1.46v on diode-check between B and E, it's likely defective.
I don't have a diagram for the module but I think someone posted one on the forum some time ago.
Yes re the PSU, it was due to a broken wire between the remote connection and the 12V supply. That is why I have not posted anything on the PSU chip, since that is not the main fault. The main fault is basically that there is no audio output. I replaced the transistor with one I had (2n3906) I know that this transistor is not a direct equivalent, but I wanted to test the amp. It still gave no output. Tomorrow I will try to use the scope to check the signals on the opamps. Re the circuit diagram for the audio part, I have found it in previous posts. I will try to do some work on it tomorrow and I will reply back with any results I have. Thanks.
Same Problem again
Hi,
This amplifier is giving me trouble again. I noticed that when I switch on with the remote wire connected to supply, the power supply of the amplifier switches on fine, but when I apply the remote voltage after switching on, the red LED remains on. The voltages of the TL494C are as follows:
Pin 1: 0.98V
Pin 2: 2.44V
Pin 3: 4.62V
Pin 4: 0V
Pin 5: 1.42V
Pin 6: 3.61V
Pin 7: 0V
Pin 8: 13.78V
Pin 9: 0V
Pin 10: 0V
Pin 11: 13.78V
Pin 12: 12.74V
Pin 13: 4.92V
Pin 14: 4.92V
Pin 15: 4.92V
Pin 16: 13.78V
Thanks
Hi,
This amplifier is giving me trouble again. I noticed that when I switch on with the remote wire connected to supply, the power supply of the amplifier switches on fine, but when I apply the remote voltage after switching on, the red LED remains on. The voltages of the TL494C are as follows:
Pin 1: 0.98V
Pin 2: 2.44V
Pin 3: 4.62V
Pin 4: 0V
Pin 5: 1.42V
Pin 6: 3.61V
Pin 7: 0V
Pin 8: 13.78V
Pin 9: 0V
Pin 10: 0V
Pin 11: 13.78V
Pin 12: 12.74V
Pin 13: 4.92V
Pin 14: 4.92V
Pin 15: 4.92V
Pin 16: 13.78V
Thanks
I don't understand. Do you mean that after the amp is powered up once that if powered down, it won't power up again?
The problem is due to pin 16 being driven higher than the voltage on pin 15.
The problem is due to pin 16 being driven higher than the voltage on pin 15.
If power is applied to the amplifier and then the remote wire is connected to supply, the amplifier will not power up (red LED remains on and does not switch to the blue LED). If I connect the remote to the supply then I apply power (on the +ve input) it powers on properly and there is sound output. If I disconnect the remote wire and then connect it again, then the LED remains RED and no audio is heard.
Hi,
I tried to remove Q17 and R4 but the fault remained the same. I noticed that if I bypass R197 for a few seconds, the power supply will turn on. I checked the resistor and it is giving the correct value. I also checked and replaced C89 but the fault remains the same. Please note that if I switch the supply of the amplifier with the remote connected, it will operate normally.
Thanks for your help.
I tried to remove Q17 and R4 but the fault remained the same. I noticed that if I bypass R197 for a few seconds, the power supply will turn on. I checked the resistor and it is giving the correct value. I also checked and replaced C89 but the fault remains the same. Please note that if I switch the supply of the amplifier with the remote connected, it will operate normally.
Thanks for your help.
Sorry for the late reply. I found the resistor out of tolerance and I replaced it and to be on the safe side I replaced the capacitor too, but the fault still remained there. I really don't know why if R197 is bypassed for a few seconds, the amp will power on (blue LED turns ON and Red LED turns OFF)
What's the DC voltage on terminals 15 and 16 about 5 seconds after the remote voltage is applied?
Are you applying remote voltage well after the B+ and ground are connected?
Are you applying remote voltage well after the B+ and ground are connected?
The remote is being applied within a few seconds. The thing is that if the remote is applied together with B+ the BLUE LED turns on and the amp is OK. If the remote is applied even 2 seconds later, the RED LED remains ON.
The voltage on Pin 16 is:
11.74V with remote voltage applied
0V without remote voltage
The voltage on Pin 15 is:
4.92V with remote voltage applied
0V without remote voltage
Thanks
The voltage on Pin 16 is:
11.74V with remote voltage applied
0V without remote voltage
The voltage on Pin 15 is:
4.92V with remote voltage applied
0V without remote voltage
Thanks
If you lift one one of R195, does the amp come on normally?
Is there any DC present across the speaker terminals, or a pop in the speakers?
Is there any DC present across the speaker terminals, or a pop in the speakers?
Hi, Without R195, the RED LED will not turn ON, but the AMP starts normally when remote voltage applied. On the speakers there is just 0.03VDC when the AMP is not loaded and OFF and 0VDC when the AMP is ON.
The value of R195 was 100r and I replaced it with same value when it was out of tollerance.
Thanks
The value of R195 was 100r and I replaced it with same value when it was out of tollerance.
Thanks
Monitor pin 12 of the 494 with your scope.
Have B+ and ground connected, then apply remote. How long of a delay, after applying remote is there for pin 12 to receive 12v?
Have B+ and ground connected, then apply remote. How long of a delay, after applying remote is there for pin 12 to receive 12v?
My opinion there can be two situations.
situation A:
1. Do not connect REM for 5 min
2. Connect REM
3. AMP turns-on normally, no red led
situation B:
1.With AMP on normally, remove REM
2. After a few seconds connect REM
3. AMP protection, red led
If the situation is B, then it is NORMAL because you have to wait one or two minute after
turn-off amplifier, before turn-on it again.
Some amps do this because may be some 'spk bump' problems or stuff like that when
you turn-off then turn-on amp fast.
situation A:
1. Do not connect REM for 5 min
2. Connect REM
3. AMP turns-on normally, no red led
situation B:
1.With AMP on normally, remove REM
2. After a few seconds connect REM
3. AMP protection, red led
If the situation is B, then it is NORMAL because you have to wait one or two minute after
turn-off amplifier, before turn-on it again.
Some amps do this because may be some 'spk bump' problems or stuff like that when
you turn-off then turn-on amp fast.
Monitored pin 12 and the voltage is going to 10.7V immediately and remains like that (i monitored for 20 seconds)