09-09-2021, 12:43 PM
Hi Rob,
Hopefully you're on the mend, but presumably to get your back fixed, you had to describe your symptoms to the doctors?
"No output" could mean almost literally anything. What evidence have you gathered so far? It's OK if you can't analyse the evidence, but for us to be able to help, we need something to go on. What have you done so far. As Jeffrey tactfully says, standard fault-finding procedures apply.
With your ear to the speaker, is there anything at all - slight mains hum or maybe a hissing noise? Any pops or clicks when you power up/power down? Is the speaker OK? Have you tried headphones? (Only try headphones if the DC offset is OK, or at least, use cheap/disposable ones). Does anything get hot when powered up? Any smells? Does the mains transformer hum mechanically, indicating it's getting power (some do, some don't). Does the mains switch light up? All basic things that could be checked with no use of tools...
Beyond that, the schematic gives plenty to go on. There should be about 30V across each of the main PSU caps, give or take the usual variables. The supply to the op-amps is +/-15V, and these are regulated by zeners, so should be within half a volt, say.
The power amp is DC coupled, but a fairly basic one. Check the voltage at the output node - the junction of R37/R39. That should be 0V, though there will no-doubt be a small offset. Anything less than 100mV or so should be OK.
What might you have disturbed when you had it apart? Check for wires incorrectly replaced, or wires accidentally broken by the folding up of the PCB. Of course, inspect everything for dry joints, and remember Trevor's last sentence especially.
Check the headphone socket, as that switches the speaker.
I note R40 (if I've correctly identified it) is cooked. Hopefully that doesn't point to something more sinister. It's part of the headphone attenuator, and will potentially warm up if running at full output for long periods, but it will get hotter still if the power amp output is jammed up against a rail. Let's hope that hasn't happened, as it will usually take out the speaker in the process.
Assuming all these checks are OK, inject a signal and follow it with your 'scope, as Jeffrey suggests. It's all any of us can do - we're engineers, not magicians.
Such open-ended question like this might just about be be OK for "stock faults", but not here. More input required!
Look after yourself while you recover,
Mark
Hopefully you're on the mend, but presumably to get your back fixed, you had to describe your symptoms to the doctors?
"No output" could mean almost literally anything. What evidence have you gathered so far? It's OK if you can't analyse the evidence, but for us to be able to help, we need something to go on. What have you done so far. As Jeffrey tactfully says, standard fault-finding procedures apply.
With your ear to the speaker, is there anything at all - slight mains hum or maybe a hissing noise? Any pops or clicks when you power up/power down? Is the speaker OK? Have you tried headphones? (Only try headphones if the DC offset is OK, or at least, use cheap/disposable ones). Does anything get hot when powered up? Any smells? Does the mains transformer hum mechanically, indicating it's getting power (some do, some don't). Does the mains switch light up? All basic things that could be checked with no use of tools...
Beyond that, the schematic gives plenty to go on. There should be about 30V across each of the main PSU caps, give or take the usual variables. The supply to the op-amps is +/-15V, and these are regulated by zeners, so should be within half a volt, say.
The power amp is DC coupled, but a fairly basic one. Check the voltage at the output node - the junction of R37/R39. That should be 0V, though there will no-doubt be a small offset. Anything less than 100mV or so should be OK.
What might you have disturbed when you had it apart? Check for wires incorrectly replaced, or wires accidentally broken by the folding up of the PCB. Of course, inspect everything for dry joints, and remember Trevor's last sentence especially.
Check the headphone socket, as that switches the speaker.
I note R40 (if I've correctly identified it) is cooked. Hopefully that doesn't point to something more sinister. It's part of the headphone attenuator, and will potentially warm up if running at full output for long periods, but it will get hotter still if the power amp output is jammed up against a rail. Let's hope that hasn't happened, as it will usually take out the speaker in the process.
Assuming all these checks are OK, inject a signal and follow it with your 'scope, as Jeffrey suggests. It's all any of us can do - we're engineers, not magicians.
Such open-ended question like this might just about be be OK for "stock faults", but not here. More input required!
Look after yourself while you recover,
Mark
