Hi, looking for decent 5v PSU's for my fiber converter I came across this Amigo I.T.E AMS47-0501000FV 5v 1A PSU.
It's full range 100 > 240VAC input and has no external optocouplers, so quite nice.
It has a LinkSwitch-CV LNK624PG switching controller which integrates all, even feedback:
It had really REALLY bad audible oscillation going on though, measuring the original Su'scon SK 400v 4.7uF primaries they had 6.5 and 9.5 in ESR respectively.
Replacing them with UCC KMG caps of equal rating made no difference though.
I had already checked the secondaries and they measured good, they where Su'scon MC 330uF & 680uF 10v caps.
But to make sure I replaced them with Rubycon ZLH 220uF 16v and Panasonic FR 1000uF caps respectively, still no difference.
Felling bummed out I tried adding SMD caps on the unpopulated position C9 right on the output, but this also made no difference.
And finally I populated the empty L3 position with an inductor but this too made no difference.
So I started poking around and realized that if I touch my multimeter probe to the drain of the LNK624 the oscillation became much worse.
Even if it was just the bare multimeter probe not connected to the multimeter.
So I figured I'll try replacing diode D5 with an ultrafast, even though the attached documentation advises against it.
There was no difference though.
Next I tried poking the feedback pin of the LNK624PG instead, and that made the oscillation much better, almost gone.
So I figured that probably resistors R4/R4A or R3 would be out of spec, but desoldering them and measuring I found they where perfectly in spec!
So I ghetto modded potentiometers in their place so I could adjust them but this also made no difference.
Well of course except for the fact that it allows to calibrate the 5v output.
At this stage I've decided to give up on it but if anyone has some ideas about what I could try I'm all ears.
Also it might help someone Googling in the future
The PCB is marked AMS47-2 REV: 01
It's full range 100 > 240VAC input and has no external optocouplers, so quite nice.
It has a LinkSwitch-CV LNK624PG switching controller which integrates all, even feedback:
It had really REALLY bad audible oscillation going on though, measuring the original Su'scon SK 400v 4.7uF primaries they had 6.5 and 9.5 in ESR respectively.
Replacing them with UCC KMG caps of equal rating made no difference though.
I had already checked the secondaries and they measured good, they where Su'scon MC 330uF & 680uF 10v caps.
But to make sure I replaced them with Rubycon ZLH 220uF 16v and Panasonic FR 1000uF caps respectively, still no difference.
Felling bummed out I tried adding SMD caps on the unpopulated position C9 right on the output, but this also made no difference.
And finally I populated the empty L3 position with an inductor but this too made no difference.
So I started poking around and realized that if I touch my multimeter probe to the drain of the LNK624 the oscillation became much worse.
Even if it was just the bare multimeter probe not connected to the multimeter.
So I figured I'll try replacing diode D5 with an ultrafast, even though the attached documentation advises against it.
There was no difference though.
Next I tried poking the feedback pin of the LNK624PG instead, and that made the oscillation much better, almost gone.
So I figured that probably resistors R4/R4A or R3 would be out of spec, but desoldering them and measuring I found they where perfectly in spec!
So I ghetto modded potentiometers in their place so I could adjust them but this also made no difference.
Well of course except for the fact that it allows to calibrate the 5v output.
At this stage I've decided to give up on it but if anyone has some ideas about what I could try I'm all ears.
Also it might help someone Googling in the future
The PCB is marked AMS47-2 REV: 01
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