"Maciej W. Rozycki" wrote: >On Mon, 2 May 2022, Peter Coghlan via cctalk wrote: > >> Thankfully, it doesn't seem to have been there long and didn't get a chance >> to spread around the board. Bizarrely this capacitor has it's legs pointing >> upwards and managed to leak while there are similar capacitors on the other >> board with their legs pointing downwards which don't seem to have leaked >> (yet?). > > Would the system have been possibly stored upside down sometime? >
I don't think so. It may have spent some time lying on it's side due to deteriorating rubber feet and for ease of access and but I can't see any reason for it ever being upside down. Once I discovered this issue a few years ago, I checked all my power supplies, removed any leaking capacitors and changed to storing the machines the right way up in a vertical stack, with newspapers between them in place of the rubber feet. I hoped this would prevent any capacitors which hadn't shown any signs of leaking from starting to leak. (Now whichever machine I want to work on always seems to be at the bottom of the stack...) > > These nasty caps do leak even while in storage (and even if never used, > not even soldered ever, according to one source, a repair professional). > They are nasty and devious. In my case, the ones that have been stored in any orientation but not used much seem to have fared better. I only started using this machine with the H7822 for extended periods for the first time a few months ago. One of the reasons I started using it more is because I thought it was immune to the leaky capacitor problem! It never saw any serious use before that, even when it was new. I have at least two machines with H7822 power supplies. Even though they have capacitors that look the same as the ones in the H7821, the ones in the H7822 power supplies didn't seem to be showing any signs of leaking when I examined them some time ago so I thought they might be from a batch that was unaffected by the problem. It seems that this was not true :-( I unsoldered the other eight similar capacitors (four one each board) from the H7822 yesterday evening. I found a small amount of leakage under most of them but it was was only evident after they were removed from the board. In general, there was less damage visible under the ones on the lower board with leads facing down oddly enough. I thought one of the capacitors from the upper board had not leaked at all. I left the removed capacitors standing on the bench overnight with their leads upwards and they all have some signs of leakage visible on them today. It's hard to draw any conclusions. The capacitor from the upper board that leaked enough for me to notice it might be under greater stress when operating than the others. I think the same capacitor in the H7821 power supplies seems to leak more in those too. Maybe it carries greater ripple current than the others or something like that? I can see that the other four similar capacitors make up PI filters for the +5V and +12V outputs along with a pair of smoothing chokes, however I can't quite figure out what the more leaky one is responsible for. It could be associated with the -12V output which might also be the supply for the fans. This part of the circuit is very hard to trace. I don't have enough spare capacitors to replace the four on the lower board. I am going to leave those out, leave the input lead to that board unplugged and plug the green LED into the upper board. I hope it will then behave just like a H7821. There won't be any power to the front disk drive connector but I am not using that so it doesn't matter unless the "power good" output is affected, in which case I will have to think of something else. I am hoping that the leaky capacitors were responsible for the odd intermittent failures I experienced with this power supply recently. Regards, Peter Coghlan. > Maciej
