hi all, my trusty A5 has finally developed a fault,
just thought i'd post it here in case anyone knows of it.
my LH channel output is severely attenuated, down to about 25% power. it sounds ok, not distorted, just low power.
ive swapped inputs and speakers around and its definatly the LH preamp or output stage.
my goto was the power transistors on the heatsink but as the power is low and not zero i'm now not so sure.
i'm capable of unsoldering and swapping components, but i dont have a test signal generator or scope.
i thought it might be an old capacitor grounding the ip signal, but to be honest i'm guessing..
any thoughts
just thought i'd post it here in case anyone knows of it.
my LH channel output is severely attenuated, down to about 25% power. it sounds ok, not distorted, just low power.
ive swapped inputs and speakers around and its definatly the LH preamp or output stage.
my goto was the power transistors on the heatsink but as the power is low and not zero i'm now not so sure.
i'm capable of unsoldering and swapping components, but i dont have a test signal generator or scope.
i thought it might be an old capacitor grounding the ip signal, but to be honest i'm guessing..
any thoughts
I found the schematic attached below via ElektroTyana.
If your internal cabling will permit, I suggest continuing your channel-swapping fault-finding by exchanging power amp inputs to their opposite channel preamps. This should allow you to localize the fault to preamp vs. power amp (PA). Alternately, you may be able to contrive a way to inject audio from an external source into the PA at LIN, CN201. Behavior in the working channel is your reference.
Beyond that, do you have a DVM and know how to probe safely? You don't want to hurt yourself or your equipment. I'd probe power supplies first to confirm correct supply voltages--- though they are likely OK, since your right channel is working.
I'm going to assume you localize the problem to the left PA--- simply a guess--- and that you can't find any defect visually. My habit is to first check amp output voltage, and voltages at bases of Q203 and Q204. These give a quick look at health of amplifier bias. Beyond that, I poke around for initial clues. The other channel is your comparative reference.
Let us know how things go. Good luck!
If your internal cabling will permit, I suggest continuing your channel-swapping fault-finding by exchanging power amp inputs to their opposite channel preamps. This should allow you to localize the fault to preamp vs. power amp (PA). Alternately, you may be able to contrive a way to inject audio from an external source into the PA at LIN, CN201. Behavior in the working channel is your reference.
Beyond that, do you have a DVM and know how to probe safely? You don't want to hurt yourself or your equipment. I'd probe power supplies first to confirm correct supply voltages--- though they are likely OK, since your right channel is working.
I'm going to assume you localize the problem to the left PA--- simply a guess--- and that you can't find any defect visually. My habit is to first check amp output voltage, and voltages at bases of Q203 and Q204. These give a quick look at health of amplifier bias. Beyond that, I poke around for initial clues. The other channel is your comparative reference.
Let us know how things go. Good luck!
Please note, this amp has already been repaired.?? dont know what this is... but i will try all the above thanks
in the photo, the left side has already undergone a repair.
I can also tell you that the PCB was dismantled with a screwdriver or an electric screwdriver.
The A5 V1 has SAP15 output, The V2 has integrated circuits like TDA but I don't know which one anymore.
I can also tell you that the PCB was dismantled with a screwdriver or an electric screwdriver.
The A5 V1 has SAP15 output, The V2 has integrated circuits like TDA but I don't know which one anymore.
The schematic above is for the A500, not A5. Is that the same?
I reckon it'll probably be a selector (switch or relay) or volume control, but...
I think there's more than one version of the A5, with the first having discrete output transistors and the second using LM3886 IC's - the pic above seems to show the latter. If so, I reckon the first step should be to compare the voltage at the input pin of each of the two LM3886's which I think is pin 10. So, probe very carefully with your multimeter set to low AC volts between pin 7 (GND) and 10 with the amp playing quietly.
The pins are counted right to left as you're looking at the chip in the photo above, noting that they are staggered so don't miss that Pin 7 is one of the back ones. I'm not sure how easy it might be to probe that one. It may be easier to probe from underneath if you can get access.
That should indicate whether it's a problem with the 'preamp' section (especially the volume control) or the LM3886's themselves.
I reckon it'll probably be a selector (switch or relay) or volume control, but...
I think there's more than one version of the A5, with the first having discrete output transistors and the second using LM3886 IC's - the pic above seems to show the latter. If so, I reckon the first step should be to compare the voltage at the input pin of each of the two LM3886's which I think is pin 10. So, probe very carefully with your multimeter set to low AC volts between pin 7 (GND) and 10 with the amp playing quietly.
The pins are counted right to left as you're looking at the chip in the photo above, noting that they are staggered so don't miss that Pin 7 is one of the back ones. I'm not sure how easy it might be to probe that one. It may be easier to probe from underneath if you can get access.
That should indicate whether it's a problem with the 'preamp' section (especially the volume control) or the LM3886's themselves.
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I should have indicated that the voltage measured will vary with input signal (music) but if one side is significantly quieter, it should be fairly obvious. Ideally you'd input a constant tone channels.