Although it will be hard to trace the fault without schematic, you could provide one or two more pictures. One overall view of the amp's inside, as close as possible and one of the solder-side.
It looks like a fairly simple design and perhaps there's only a mute circuit acting as a protection for DC at the output. The components in the top right corner of the first picture could be that circuit.
What measuring equipment do you have at hand?
/Hugo
It looks like a fairly simple design and perhaps there's only a mute circuit acting as a protection for DC at the output. The components in the top right corner of the first picture could be that circuit.
What measuring equipment do you have at hand?
/Hugo
Thanks again for your help mate.
I have a multimeter and attached are 3 pictures. Hope that they are good enough, else I can always take more.
First picture:
2nd picture:
3rd picture:
I have a multimeter and attached are 3 pictures. Hope that they are good enough, else I can always take more.
First picture:
An externally hosted image should be here but it was not working when we last tested it.
2nd picture:
An externally hosted image should be here but it was not working when we last tested it.
3rd picture:
An externally hosted image should be here but it was not working when we last tested it.
Make sure the amp is turned off.
With your DMM in AC mV range connect the ground lead to the black wire between to two big caps as seen in your first picture (fky6h4). The other lead should go to TP3(-) and for the other channel TP?(-).
With the volume knob at zero, apply a signal to the amplifier, switch the amp on and turn up the volume a little bit, say 1 or 2 if the dial goes to 10.
If the meter responds for both TP's, you have a big chance that only one of the two output fuses has a bad contact. Both output fuses are the glass cylinders located nearest to the big capacitors.
/Hugo
With your DMM in AC mV range connect the ground lead to the black wire between to two big caps as seen in your first picture (fky6h4). The other lead should go to TP3(-) and for the other channel TP?(-).
With the volume knob at zero, apply a signal to the amplifier, switch the amp on and turn up the volume a little bit, say 1 or 2 if the dial goes to 10.
If the meter responds for both TP's, you have a big chance that only one of the two output fuses has a bad contact. Both output fuses are the glass cylinders located nearest to the big capacitors.
/Hugo
Just above the opamp TL072 you can see two capacitors.
On the third picture (fn4hnm) you can see some kind of stain surrounding them. If you have no idea where it comes from, (spray can to clean contacts?) they might be leaking. Change them and clean the pcb with isopropanal or some alcohol you have at hand.
/Hugo
On the third picture (fn4hnm) you can see some kind of stain surrounding them. If you have no idea where it comes from, (spray can to clean contacts?) they might be leaking. Change them and clean the pcb with isopropanal or some alcohol you have at hand.
/Hugo
Hi Hugo,
I did a quick check and below are my findings:
1)Both fuses seems to be working fine.
2) You are correct that the capacitor above opamp TL072 is leaking. I will source for the components and change it.
Questions again:
1) The leaking cap shows HFS 100UF 25V, should I buy back the same or can I buy better ones?? Read that BC sounds good on many other amps. Any good reccomend?
2) Should I change the two big capacitors Rubycon 6800UF 50V to 10000UF 50V??
I am doing these purchases b'cos many vendors have a minimum order.
Many thanks again.
Regards,
Bernard
I did a quick check and below are my findings:
1)Both fuses seems to be working fine.
2) You are correct that the capacitor above opamp TL072 is leaking. I will source for the components and change it.
Questions again:
1) The leaking cap shows HFS 100UF 25V, should I buy back the same or can I buy better ones?? Read that BC sounds good on many other amps. Any good reccomend?
2) Should I change the two big capacitors Rubycon 6800UF 50V to 10000UF 50V??
I am doing these purchases b'cos many vendors have a minimum order.
Many thanks again.
Regards,
Bernard
Hi - clean the board after taking out the leaking capacitor, but BEFORE installing the new one(s).
You can test the amplifier system to see if its OK before you install the new capacitor(s).
You may want to change the other capacitor as well, just in case its on the verge of leaking. It's important to remove all the 'oily stain'; clean on both sides of the board. Hopefully after this the amp will be fine.
Cheers!
You can test the amplifier system to see if its OK before you install the new capacitor(s).
You may want to change the other capacitor as well, just in case its on the verge of leaking. It's important to remove all the 'oily stain'; clean on both sides of the board. Hopefully after this the amp will be fine.
Cheers!
Thanks Clem_o for the advise.
Hi Hugo and all kind souls,
I had cleaned the board with contact cleaner and change both the capacitors. However the problem still exists. After spraying the board with contact cleaners, the problem actually worsened. Sound from left channal is very soft, almost no sound, and it will not recover even after changing both capacitors.
Pls help!!
Thanks all.
Hi Hugo and all kind souls,
I had cleaned the board with contact cleaner and change both the capacitors. However the problem still exists. After spraying the board with contact cleaners, the problem actually worsened. Sound from left channal is very soft, almost no sound, and it will not recover even after changing both capacitors.
Pls help!!
Thanks all.
Hmm. If you have a multimeter, set it to read DC volts, and with the speaker NOT connected, check voltage at the output pins of the TL072 that was near the oil stain. Measure the voltage from pin 1 to ground, and also pin 7 to ground.
TL072 pin number as follows:
1 U 8
2 . 7
3 . 6
4 . 5
Both readings should be zero. If not, there's still an electrical leakage; more cleaning needed.
Hope this helps!!
TL072 pin number as follows:
1 U 8
2 . 7
3 . 6
4 . 5
Both readings should be zero. If not, there's still an electrical leakage; more cleaning needed.
Hope this helps!!
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