Okey, just did some testing:
Lifted both pin 3 and 5 from IC11. This is the feed from the PWM-circuit.
NOW the thing makes sound, rail-2-rail osc. and more!
Input-pin 3 on IC14 and IC15 now got (almost) square shaped oscillation waveforms.
Rail to rail waveform at output transistors is perfectly sawtooth-shaped (is that the right shape?).
My 400Hz sinus signal at the RCA's now make it all the way to the speaker.
Its amplitude can also be controlled via gain, x-over and more.
However it cuts into protect as soon as I increase the gain too much (this could be due to insufficient power access though, as my p.sup only provides 5A at the moment (got a 50 Amp car battery available tomorrow)).
So: what exactly is that PWM circuit intended to do?
As I mentioned earlier, pin 13 at IC9 (CD4013) outputs a perfectly squared waveform signal.
Although sawtooth-shaped, the PWM-output that enters pin 3 and 5 at IC11 seems a bit distorted. This applies even now when those pins are lifted. I'm not exactly sure of what it should look like. 😕
Could it be that C52 and/or C53 no longer are within tolerance?
Lifted both pin 3 and 5 from IC11. This is the feed from the PWM-circuit.
NOW the thing makes sound, rail-2-rail osc. and more!
Input-pin 3 on IC14 and IC15 now got (almost) square shaped oscillation waveforms.
Rail to rail waveform at output transistors is perfectly sawtooth-shaped (is that the right shape?).
My 400Hz sinus signal at the RCA's now make it all the way to the speaker.
Its amplitude can also be controlled via gain, x-over and more.
However it cuts into protect as soon as I increase the gain too much (this could be due to insufficient power access though, as my p.sup only provides 5A at the moment (got a 50 Amp car battery available tomorrow)).
So: what exactly is that PWM circuit intended to do?
As I mentioned earlier, pin 13 at IC9 (CD4013) outputs a perfectly squared waveform signal.
Although sawtooth-shaped, the PWM-output that enters pin 3 and 5 at IC11 seems a bit distorted. This applies even now when those pins are lifted. I'm not exactly sure of what it should look like. 😕
Could it be that C52 and/or C53 no longer are within tolerance?
Update:
Resoldered pin 3 and 5 on IC11 back to the board.
Observing pin 1 from IC12 (this goes directly to pin 3 and 5 on IC11):
It's only 1.2V - yet its input on the comparator (5.58V on pin 2 and 9.30V on pin 3) tells me that this pin should be high!
Well, it's not!
I then lifted pin 1 on IC12 from the board and measured directly at the pin: it's still low at 0.0V!
Pin 3 and 5 on IC11 (PWM) now got 29.0V at its legs - and...
The amp is now all working!! 🙂
Rail to rail oscillation waveform is now square shaped, and the PWM line waveform is clean sawtooth shaped!
I believe that I must have re-destroyed IC12 (section A) while replacing it. Overheat may have been the cause for that.. 🙁
Before I open the Champagne, I'll re-order some LM393's and replace IC12 once more..
Resoldered pin 3 and 5 on IC11 back to the board.
Observing pin 1 from IC12 (this goes directly to pin 3 and 5 on IC11):
It's only 1.2V - yet its input on the comparator (5.58V on pin 2 and 9.30V on pin 3) tells me that this pin should be high!
Well, it's not!
I then lifted pin 1 on IC12 from the board and measured directly at the pin: it's still low at 0.0V!
Pin 3 and 5 on IC11 (PWM) now got 29.0V at its legs - and...
The amp is now all working!! 🙂
Rail to rail oscillation waveform is now square shaped, and the PWM line waveform is clean sawtooth shaped!
I believe that I must have re-destroyed IC12 (section A) while replacing it. Overheat may have been the cause for that.. 🙁
Before I open the Champagne, I'll re-order some LM393's and replace IC12 once more..
Solved!
A second time replacement of IC12 did the trick! 🙂
One wouldn't actually expect a newly replaced component to be faulty as the solder tip leaves its last leg, but so it was.. 🙁
The amp is now fully assembled, mountet in its belonging car and testet to its owners satisfaction!
What startet with a loose transformer connection for the +15V/-15V rail, ended up with hours and hours of trouble shooting a second problem possible developed by the erratic voltages a hair crack gap between this almost fully broken winding in the transformer caused.
I believe the supply voltage to IC12 had exceeded the AMR in the first case.
Fixing a broken winding and replacing an 8 legged chip, normally should take approx 10 minutes... 😀
-So this wasn't exactly a "fortune income service", but I've definitively learned alot throughout this journey.
I wanna thank especially Perry Babin for his tutorial guidance which in the end lead me to a fully functioning device!
Now its time for that Champagne...
Greetings from Norway!
A second time replacement of IC12 did the trick! 🙂
One wouldn't actually expect a newly replaced component to be faulty as the solder tip leaves its last leg, but so it was.. 🙁
The amp is now fully assembled, mountet in its belonging car and testet to its owners satisfaction!
What startet with a loose transformer connection for the +15V/-15V rail, ended up with hours and hours of trouble shooting a second problem possible developed by the erratic voltages a hair crack gap between this almost fully broken winding in the transformer caused.
I believe the supply voltage to IC12 had exceeded the AMR in the first case.
Fixing a broken winding and replacing an 8 legged chip, normally should take approx 10 minutes... 😀
-So this wasn't exactly a "fortune income service", but I've definitively learned alot throughout this journey.
I wanna thank especially Perry Babin for his tutorial guidance which in the end lead me to a fully functioning device!
Now its time for that Champagne...
Greetings from Norway!
It is rare for an op-amp or comparator to fail when installed. You may want to check your iron to make sure there is no electrical leakage to the tip.
For driver ICs like the IRS21844S and similar ICs, it's much more common for them to fail when they're installed. They're relatively fragile. They can be damaged if they're heated too much when they're being installed. They're also rarely stored or prepped correctly. They require baking for xx amount of time at xx degrees to drive out any moisture that they've absorbed. Failure to do so causes them to 'popcorn' and fail on installation.
For driver ICs like the IRS21844S and similar ICs, it's much more common for them to fail when they're installed. They're relatively fragile. They can be damaged if they're heated too much when they're being installed. They're also rarely stored or prepped correctly. They require baking for xx amount of time at xx degrees to drive out any moisture that they've absorbed. Failure to do so causes them to 'popcorn' and fail on installation.
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