Hi All
I'm a complete newbie to this forum and I am looking for some help. I also know very little about electronics so please bear with me.
I have owned this amp for about 2 years, having bought it second hand. About 6 months ago it developed an intermittent fault - the LH channel cuts out or goes very quiet and only comes back if I nudge or tap or press the front of the case. At first I thought I needed to tap the volume or balance control, and so thought it might be those potentiometers but have realised that I can press anywhere on the front or top of the case and it resolves. I have taken off the case top and can see no obvious issues with loose wires etc, and have found that I can make the LH channel go and comes back even by pressing on the rear of the circuit board with a screwdriver. It's as if there is a loose connection somewhere which is highly sensitive to movement of the circuit board.
The issue is present on the same channel on both sets of speakers.
Any advice would be gratefully received.
Cheers.
I'm a complete newbie to this forum and I am looking for some help. I also know very little about electronics so please bear with me.
I have owned this amp for about 2 years, having bought it second hand. About 6 months ago it developed an intermittent fault - the LH channel cuts out or goes very quiet and only comes back if I nudge or tap or press the front of the case. At first I thought I needed to tap the volume or balance control, and so thought it might be those potentiometers but have realised that I can press anywhere on the front or top of the case and it resolves. I have taken off the case top and can see no obvious issues with loose wires etc, and have found that I can make the LH channel go and comes back even by pressing on the rear of the circuit board with a screwdriver. It's as if there is a loose connection somewhere which is highly sensitive to movement of the circuit board.
The issue is present on the same channel on both sets of speakers.
Any advice would be gratefully received.
Cheers.
I think it is caused by a bad speaker output relay.
To test it, bypass the relay outputs by soldering wires on them and test to confirm the amp 'no DC output' before you connect to speaker to listening.
To test it, bypass the relay outputs by soldering wires on them and test to confirm the amp 'no DC output' before you connect to speaker to listening.
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It is also common caused by dry soldering joints and cracks on the PCB, please careful check the PCB soldering condition first.
I found this low-res. set of still pics of the Alpha 7 innards on You tube: YouTube tube
As you can see its a single, full chassis sized PCB for rigidity of the lightweight enclosure but that also means the connections to the PCB such as pots, switches and everything else not mounted solely to the PCB, is under stress when you push the panels. This may explain why the sound returns when you push the front panel.
I would carefully (as in don't use any metal tools that might short out sensitive circuits in there) inspect what happens when you press the case panels with the cover off and see if you can locate what moves and possibly re-connects the necessary circuit(s) when you have it powered up in this open state. It could be speaker connections at the rear or controls at the front where a cracked solder joint or displaced connector lead has resulted in the sensitivity to physical force, so it may not be that hard to trace.
Don't ignore the fact that there is mains voltage to the transformer and power switch in there and live connectors may be exposed so don't take this adventure lightly - mains AC kills. If this is a step beyond your comfort zone, enlist the help of someone who is at least familiar with electrical repairs and safety precautions.
As you can see its a single, full chassis sized PCB for rigidity of the lightweight enclosure but that also means the connections to the PCB such as pots, switches and everything else not mounted solely to the PCB, is under stress when you push the panels. This may explain why the sound returns when you push the front panel.
I would carefully (as in don't use any metal tools that might short out sensitive circuits in there) inspect what happens when you press the case panels with the cover off and see if you can locate what moves and possibly re-connects the necessary circuit(s) when you have it powered up in this open state. It could be speaker connections at the rear or controls at the front where a cracked solder joint or displaced connector lead has resulted in the sensitivity to physical force, so it may not be that hard to trace.
Don't ignore the fact that there is mains voltage to the transformer and power switch in there and live connectors may be exposed so don't take this adventure lightly - mains AC kills. If this is a step beyond your comfort zone, enlist the help of someone who is at least familiar with electrical repairs and safety precautions.
Hi Ian, I really appreciate the time you’ve taken to post that very detailed reply. I’ll whip the cover off again and do as you suggest. If I can’t resolve it myself I guess I will find a repair shop to have a look but with the current situation that won’t be any time soon. Cheers