I love watching your videos. The data sheet actually says that the Ref voltage has a spread from/to at 25 deg C. I am not a fan of changing the cap type you replaced the blue "film" cap with a multilayer ceramic cap, these have poor value with heat and or voltage unless you specify the temperature coefficient when you order them, like NP0 X5R X7R etc. But depending on the circuit location it may or may not be a problem. All the best Rich
@Tony359_2
Сағат бұрын
oh... I thought they were the same type! That was not intentional for sure. Can you tell me more?
@tw11tube
46 минут бұрын
At that location, I don't think a multilayer ceramic capacitor (MLCC) will be a problem. The originally blue capacitor is likely the cap in the negative feedback from cathode to ref at the TL431. The ref voltage is ~2.5V, and the cathode will be at around 5V - 1.5V (forward voltage of the IR LED in the optocoupler), which is around 3.5V, so there will be 1V over the cap. This is *way* below the rated voltage, so capacity loss is not dramatic. Furthermore, as long as the circuit does not oscillate, the capacitor does its job just fine. Probably you don't need 100nF to suppress the oscillation, but something like 30nF would work in most circumstances and the remaining capacity is just margin.
@Tony359_2
28 минут бұрын
that's great to hear! So for next time I should get a "film" capacitor instead?
@anvz6
Сағат бұрын
The reference voltage does not matter at all if it's fixed. Any voltage in range of the divider will provide a perfectly stable output voltage controlled by the trimmer. The reference itself is not important. What is important is it's stable.
@Tony359_2
Сағат бұрын
absolutely - I think I got that in the end but I made a little confusion at the beginning! Learning as I go :)
@Dutch-linux
2 сағат бұрын
timestamp 12:14 there is also a transistor of some sort... is that defective and reacting on temp changes ?
@Tony359_2
Сағат бұрын
that's the TL431 :)
@maxtornogood
4 күн бұрын
Some failures are more subtle than what we are used to seeing. Swapping those pieces out has it a lot more stable now!
@Tony359_2
4 күн бұрын
I hope so! Though I might discourage repairs on this model of PSUs if those capacitors self-destruct so easily.
@GaRbAllZ
Сағат бұрын
45 mV??? Did you take temp delta of the Fluke into account? Just curious...
@Tony359_2
Сағат бұрын
no, but you might be reaching the end of the video soon :)
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