I have a Yamaha CA-X1 (610) which left channel's TA7136p becomes problematic sometime until it finally dies thundering crackling sound then the left channel is completely gone i thought it was the differential pair which highly unlikely , i just serviced this amp few months ago, replaced all caps and transistors including the 4 outputs transistors, anyway i ended up using the TA7136p from phono section which works fine, while waiting for OPA604AU to arrive. i didnt know the OPA604AP was currently still available at mouser,.... anyway when the OPA604 (SMD package) arrived i have to buy sop-8 to dip adapter and pin map the legs correctly which i did and i added 0.1uf ceramic cap across opamp's pin 4 and 7, removed the components from pin 5 and pin 1 that OPA604 not needed, i did the same thing for right channel . after power on it works but suddenly left channel did a thundering crackling sound, meters going crazy, but after a while it settles it works fine after a few minutes of power up, this happens when the amp is turned off for quite some time and newly powered up, i tried using it every day for a week and the issue is fading away everytime i used the amp frequently to the point that the noise when starting up completely gone, but after 3 days of not using it, the issue came back, i replaced it with new OPA604, it did the same thing, tried swapping the OPA604 from the right channel still to no avail, i just notice that the right channel is doing this to but really rare and subtle to notice. The amp is working fine but not porperly, just sounded a bit warm which and bassy still sounds great this is not how it sounds before, just wait for a few seconds to after the crackling sound is gone before for you to use it, i also tried replacing ceramics caps C475, C407, and all resistors are fine, is there something im missing? any modification i missed? im clueless now,, help . i removed the circled components..(Mind you that PIN 2 in this schematic is the non-inverting input and PIN 3 is the inverting)
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Maybe check for dry solder joints, google for pix, need a magnifying lamp. Also check solder joints on voltage regulators, especially those with heatsinks.
Is the thundering and crackling sound affected by the volume control? I would clean all the switches in the unit with contact cleaner.
Get some ice spray and cool down any semi conductor in the amp. This can show you some defective part that may recover when getting warm.
Check all the recently replaced capacitors for the right polarity. You may have made a mistake.
Watch the power supply voltages with an osciloscope while turning the amp on. A rectifier diode may have problems.
Check all the recently replaced capacitors for the right polarity. You may have made a mistake.
Watch the power supply voltages with an osciloscope while turning the amp on. A rectifier diode may have problems.
I have no quarrel with any of the suggestions above--- they seem to be good ideas. But having the circuit in the failed state may present a good opportunity to troubleshoot bias related problems.
A working opamp in this circuit will have output, inverting input, and non-inverting pins all measuring 0VDC. First check the output pin voltage. If it's 0V, the opamp is probably biasing correctly, and the problem is likely elsewhere.
But with luck, you might find the output is stuck on a supply rail. If so, note the voltage and then follow feedback through R417 leads back toward the inverting input pin. You should find the input pin attempting to bias toward the opamp output voltage, but you might find an open along the path.
Alternately, if you find the inverting input is following the output, you can be fairly certain the bias path to the non-inserting pin has opened and the pin has drifted toward one of the supply rails. Because the opamp has low bias current, this drift may happen very slowly.
BTW, with the OPA604 replacing the original IC, I would delete C745, as it might provoke oscillation.
Good luck!
A working opamp in this circuit will have output, inverting input, and non-inverting pins all measuring 0VDC. First check the output pin voltage. If it's 0V, the opamp is probably biasing correctly, and the problem is likely elsewhere.
But with luck, you might find the output is stuck on a supply rail. If so, note the voltage and then follow feedback through R417 leads back toward the inverting input pin. You should find the input pin attempting to bias toward the opamp output voltage, but you might find an open along the path.
Alternately, if you find the inverting input is following the output, you can be fairly certain the bias path to the non-inserting pin has opened and the pin has drifted toward one of the supply rails. Because the opamp has low bias current, this drift may happen very slowly.
BTW, with the OPA604 replacing the original IC, I would delete C745, as it might provoke oscillation.
Good luck!
this is what im pondering about in the past few days, my initial thought was to remove this, threads in audiokarma didnt say this so i didnt touch it, might remove this cap later
the tricky part is, the issue only occurs for a few secs, like 30 maybe less and then it goes away , you have to turn off the amp for few hours and turn it on again for the issue to appear again. my freeze spray ran out , waiting for it to arrive last time i checked i have a 100-150mv dc its jumping like crazy some times up to 200mv on pin 6 and 10-30mv on inverting inputs ,but when i install this chip to other channel it turns out to be alright, might be an parasitic oscillation.
As a thought experiment, let's assume the opamp isn't banging rail-to-rail, i.e. it's responding linearly to signals it's presented with. This means that both the non-inverting and inverting inputs (+ and - for convenience) have to be dynamically identical. If the + input were noise free, the - input would have to also be noise free. But you observe the converse--- I believe this implies the noise has to originate before the + input. As a diagnostic test, I suggest removing R409 and installing a short across from + input to ground. You won't have any audio, but there should be no erratic noise. If no noise, remove the short but leave R409 open; now you're testing R411 as the noise culprit.
Assuming the noise maker still precedes the opamp, but R411 is absolved, I'd reinstall R409 and try a "divide and conquer" search for the defect. Maybe open signal at terminal L1 and determine presence or absence, then devise the next test about midway in the unknown, etc.
If the problem disapears after use and needs days (!!!) to reappear, I think an electrochemical process in an electrolytic running at wrong polarity could be the problem. If the reversed voltage is not too high, it may not instandly blow, but change internaly. First I would check any coupling capacitor.
its just needs 12hrs at least,
i double checked it , all caps and polarity are fine, this amp is working fine , the issue appears when i change the opamp in the pre amp section....
Not gonna lie, i considered this, well not leaving it on all the time but, power it up once everyday and already tried this for almost a week and it turn out fine, i think its my OCD , i cant stand that its not working properly.... might also add,, its now sounds a tad warmer like tubey, or marantz like signature which i notice immediately, it was close to flat before the opamp replacement...
I was referring to the contact of the conductive layer with the wire terminal. It is very likely that you will not see it.
oh yeah, the wires from main board to tone control, the 6 or 5 wires i guess the one you have to twist right?
