Paul BarnfatherLinn Majik DSM audio amplifier repair
PeerTube
HannesWI would be interested in how you where able to pinpoint the issue to that specific capacitor? I have seen that warmed up capacitors do seem to work better, but only realized this when you called it out explicitly. For other interested in this: https://electronics.stackexchange.com/a/350804
@hannesw sure! I didn't dwell on it much in the video, but the symptoms were:
1. Device doesn't switch on when cold
2. Device switches on when circuit is warmed
3. Device works normally once switched on (even when cold)
That points to a fault with the "starter" capacitor on the switch mode power supply. These are usually a small-ish electrolytic (~10-47uF) with a high-ish voltage rating (~20-50V). They're energised continuously by the supply voltage, so are prone to failing early - especially in the UK where our supply voltage is often >240V.
So it was a case of finding that particular cap. I was lucky to find a report of another Linn with the exact same fault (although the capacitor was elsewhere on that particular power supply). After that, I just had to find the suitably-valued electrolytic nearest the switch mode chip...
1. Device doesn't switch on when cold
2. Device switches on when circuit is warmed
3. Device works normally once switched on (even when cold)
That points to a fault with the "starter" capacitor on the switch mode power supply. These are usually a small-ish electrolytic (~10-47uF) with a high-ish voltage rating (~20-50V). They're energised continuously by the supply voltage, so are prone to failing early - especially in the UK where our supply voltage is often >240V.
So it was a case of finding that particular cap. I was lucky to find a report of another Linn with the exact same fault (although the capacitor was elsewhere on that particular power supply). After that, I just had to find the suitably-valued electrolytic nearest the switch mode chip...
@clanger9 Pretty cool, thanks for the elaborate explanation, much appreciated. If I may, I would be interested in understanding what the "starter" capacitor is. You wouldn't have any link to a schematic or such?
@hannesw good question! Looking at a TOP232/233 diagram, I'm wrong to call it a "starter" capacitor. I think the capacitor I replaced is actually C5 in these diagrams, which is the smoothing capacitor on the feedback side https://www.power.com/sites/default/files/documents/topswitch-fx_family_datasheet.pdf