Electronics > Repair
OPA150 Stereo AMP issues, only turns on when I physically heat it up w/ a dryer!
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N19htmare:

--- Quote from: wraper on August 30, 2020, 12:32:04 am ---As it seems from the photos this is purely analog stuff with no digital controls. Relay which clicks should be from output protection circuit. It may fail to enable output because some of the channels have issues, however as it works fine when you manage to switch it on, it's probably not. So IMHO the main suspect is protection circuit. Two boards with a blue Goodsky relay on it seems to incorporate amplifier output stage + protection circuit. Protection circuits probably are interconnected to shut down both channels if abnormal condition is detected on either of them. I would first try measuring output voltages from both amplifiers (before protection relay) without any input signal to see if they are fine (around 0V). You can also try heating one of those side boards at a time to see if heating some particular board allows to switch amplifier on.

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Without input and amp on, I'm not getting any voltage on the outputs, once Ive plugged in the line in signal, that i start getting v.


--- Quote from: wraper on August 30, 2020, 12:40:28 am ---
--- Quote from: N19htmare on August 30, 2020, 12:16:36 am ---Also for the diode/zener, I don't see any markings, just the black polarity line, I'll check again after removing it

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I have tried that and it is not until I apply heat to the group of resistors next to the opamp that I get it working.
Try heating NJM4560L opamp (U6) with soldering iron. Simply touch it's case with soldering iron for say 10 seconds and see if it allows to switch amplifier on without heating rest of the board.
wraper:
Maybe try measuring voltage across ZD6 while cold, then measure while heating and see if it changes significantly.
N19htmare:

--- Quote from: wraper on August 30, 2020, 12:52:02 am ---Maybe try measuring voltage across ZD6 while cold, then measure while heating and see if it changes significantly.

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Here are readings I got at multiple state. Some of the information answers a couple of my prior questions also!.

FULLY COLD but with power on the voltage across ZD6 is 9.59V.

When warmed up and amp fully working, the voltage across ZD6 is 10.2V.

Observation: While the amp is working the votage across ZD6 is constantly dropping. AS SOON AS IT REACHES 9.74V, THE RELAYS CLICK OFF!. The rate of temperature drop is relative to the surrounding temp. If it stays warm enough, the temp will not drop below 9.74V for a while and it keeps working. However if I'm blowing around that area to cool it down, the voltage drops faster.

As I warmup the area, the temp RISES and once it's over 9.75ish V, the amp turns on.

I think this explains the reason the amp clicks off/on when my printer/ac turn on. I think theres enough Vdrop that it goes below 9.74V momentarily causing the relays to shut off.


Bad diode or something else?
N19htmare:
accidental double post.
wraper:
Quite likely faulty zener diode. Most likely there is marking on the opposite side of it, from which we can figure out its rated voltage. But you will need to desolder it to see the marking.
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