Author Topic: Help identify component  (Read 979 times)

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Offline giosifTopic starter

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Help identify component
« on: August 31, 2019, 07:13:16 am »
Hi,

I am in need of help figuring out the component in TO-92 package in the attached picture.
This was taken out of a SMPS for Amiga A500 (i.e. "lightweight" version) that is not working (it emits a cycling click sound and the output is fluctuating - I think the supply keeps restarting).
The component sits specifically in the section which provides the feedback for the 5V rail.
I suspect it is a variant of LM431 / TL431, but could someone please help confirm?

Thank you!
 

Offline Chriss

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Re: Help identify component
« Reply #1 on: August 31, 2019, 07:38:14 am »
I agree too does it could be some of the TL431.
My method to be more sure when I run in such of problem is to check how is the part wired up in the original circuit and then I check from datasheet or on the net how others are wired up.
When the wiring is  very similar or in many cases  almost the same as in the datasheet.

Sent from my SM-J500F using Tapatalk

 

Offline giosifTopic starter

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Re: Help identify component
« Reply #2 on: August 31, 2019, 08:00:19 am »
That was quick!
Thank you both for the confirmation!
I've replaced it with a TL1431, which seems to have the same specs as a TL431.
However, this was not the issue with the power supply (kind of tells how much I understand SMPS's).
 

Offline ArthurDent

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Re: Help identify component
« Reply #3 on: August 31, 2019, 12:43:31 pm »
I think that a clicking sound from a SMPS is generally caused by the supply trying to start then detecting a short so the supply shuts down and tries again and this cycle continues. If the supply is doing this with no load, some supplies will not start without a load and this is true of a lot of PC power supplies. From videos it appears if this is an Amiga A500 supply that it should work without a load and at the end of this video it shows someone checking the output voltage. The most likely problem of a SMPS this age would be the electrolytic capacitors and I would suspect them first.


 

Offline giosifTopic starter

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Re: Help identify component
« Reply #4 on: August 31, 2019, 08:46:16 pm »
Yes, got caught with that in the past (i.e. measuring output from a power supply with no load) and thought this time I was doing things right: I added a load on the 5V power rail, since that one was involved in the feedback loop.
But I clearly do not understand power supplies as, after checking and double-checking pretty much all components (thankfully, the design of this SMPS is simple, with not that many components), I decided to plug it into an Amiga A500 and turn it on.
And, what do you know: the clicking stops and power rails all measure as expected.  :-+ for the power supply,  :palm: for me for getting caught again
 


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