Things I learn over and over.... - Page 1
Forum section: electronics / general

author: forrestc
author_rank: Unknown
timestamp: March 25, 2017, 02:33:23 am
content: In thecategory....Over the last 2 days I spent several hours troubleshooting before discovering that one of the 20 year old electrolytic capacitors in the piece of test equipment I was trying to repair has failed. Showed up immediately on the ESR meter. And 100% consistent with the failure mode I was seeing and trying to track down.I know this. In fact, I've fixed many pieces of equipment just by running around the board with a decent ESR meter. And I also know that this is something you should just check just after you check all the voltages.... And in fairness I did check the voltages and ripple of all of the other supplies, so I indirectly checked most of them.It's always frustrating when you waste a whole bunch of time troubleshooting a problem which turns out to be something simple you should have checked first.....

author: Brumby
author_rank: Unknown
timestamp: March 25, 2017, 05:15:32 am
content: Quote from: forrestc on March 25, 2017, 02:33:23 amI know that song.It doesn't come around nearly as often these days - but it does come every now and then.

author: Nusa
author_rank: Super Contributor
timestamp: March 25, 2017, 06:16:19 am
content: I find the last thing I fix seems to solve the problem, regardless of what order I fix things in.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 25, 2017, 07:01:49 am
content: Quote from: Nusa on March 25, 2017, 06:16:19 amYea, it's odd, I always seem to find lost items on the last place I look, every time.Edit: added 'lost items', removed 'things' (it is a joke for those who are guessing)

author: igendel
author_rank: Frequent Contributor
timestamp: March 25, 2017, 07:27:11 am
content: Quote from: tpowell1830 on March 25, 2017, 07:01:49 amNot *that*odd, actually... by definition you'll find something on the last place you look

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 25, 2017, 07:34:07 am
content: So, to save time, you should think about what would be the last place to look, and then look there first.It's especially fun when someone else has spent a couple hours troubleshooting, gives up and asks you for help. Then you come in and replace the fuse... or plug in the line cord... and it's fixed!

author: SeanB
author_rank: Super Contributor
timestamp: March 25, 2017, 07:58:31 am
content: I did that with avionics, first rule was check power supply voltages, then pop the scope probe on them, and look at the ripple voltage there. Not too concerned about value if under 100mV pp but always checked there were no missing points with a failed diode, or that there was not a big hump of shorted diodes. Some of the secondaries were fine as they had a high resistance, so would be fine for a while with a shorted diode, but not the 5V rail, which had a nasty failure of making a box full of compressed smoke, and failing eventually by blowing 2 of the mains fuses after the transformer had melted itself into a pool of goo along the entire cabinet. Yes, even those were repairable, but the cost, plus the time to redo almost half of the wire wrapped joints to replace the connectors buried in the goo, and the cleaning. PSU itself would simply be dropped into the bin of stuff for secure destruction, no way to fix that economically, even at the price of the replacement ones, you kept 3 screws and changed the rest.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 25, 2017, 08:16:55 am
content: Quote from: alsetalokin4017 on March 25, 2017, 07:34:07 amYes, I have gotten those hate looks a few times doing that as well. Talking about an evil eye, woohooo. You can lose friends that way.

author: tooki
author_rank: Super Contributor
timestamp: March 25, 2017, 10:50:18 am
content: Quote from: Brumby on March 25, 2017, 05:15:32 amHas anyone written a song about electrolytic capacitors yet?Maybe we can ask Bigclive to do one!http://youtu.be/ioAq7PI1Uwg

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 25, 2017, 11:50:22 am
content: A few days ago I needed to use a particular piece of equipment but couldn't find it. Looked high and low, looked for it off and on for several days, finally concluded that it must have been stolen along with a few other things missing from our front porch work area. So I went out and bought a new one, used it, and then went to put it away in a good place. And what do you think I found sitting right there in that place....

author: mrflibble
author_rank: Super Contributor
timestamp: March 25, 2017, 12:40:16 pm
content: Quote from: alsetalokin4017 on March 25, 2017, 11:50:22 amYup... If you really can't find that one item you need, just buy another one. Within a week or so, you'll have two!

author: TheDane
author_rank: Regular Contributor
timestamp: March 25, 2017, 05:18:10 pm
content: Quote from: forrestc on March 25, 2017, 02:33:23 amFaulty equipment is never fun, and it can be hard to track down all the trouble it can cause.It's great to hear you took the time and did the effort to locate the issue!I recently had my power supply go bad on me too - it decided to periodically do a massive voltage overshoot on power on, resulting in the immediate destruction of the EUT. Fortunately it had an analogue meter, so the fault was quickly revealed as the needle whacked itself all the way to the right edge, making a clonk noise. I suspect it's bad caps in the feedback section, but I haven't had the time to check it - I turn it on without load, and it works.And, the cost of new power supplies today are dirt cheap, so it's hard to justify spending a lot of time faultfinding on an 25 year old 0-30V, 2A Supply - especially when the switching ones usually have 10+ amps output. The ripple is worse though, but that's what filters are forA nice reminder to use all the senses when working, not just the common one