Power supply repair. - Page 1
Forum section: electronics / repair

author: chartle
author_rank: Contributor
timestamp: March 18, 2013, 02:56:56 pm
content: OK first postSeeing Dave in these videos has got me into the hey I can fix stuff too kick.I have a Dell KVM (keyboard video mouse) switch that's dead. After doing some research I found out that these devices rarely last more than 3 years (about what we got) before the power supply dies.I bought a new replacement and thought hey maybe I could fix this one as a back up. (ETA: I bought a new KVM not power supply so I don't have to worry about messing this up)So I have it open and the PS is in a neat little board off to the side. From looking at some youtube videos its seems like blown caps are usually the culprit. At first glance i don't see any thing wrong but one of the caps has a bit of a dome to the top. Its just not flat. So I guess I should go for that first.Note: My only testing equipment is a DMM from Harbor Freight (the good one if you can even say anything from Harbor Freight is good). I don't have a scope or anything else like even a power supply that can pump out the +/- 5 volts that the unit uses.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: March 18, 2013, 03:07:06 pm
content: Since you have no test equipment, the only test left is the "shotgun" approach. And that is replacing parts until the thing works.Since you see a cap with a "domed" top it is very likely to be bad. Other caps may look ok but no way of telling without test gear. Probably best to replace them all, cant be that many anyway.

author: KuchateK
author_rank: Regular Contributor
timestamp: March 18, 2013, 03:11:39 pm
content: Change the caps. I fixed few devices with caps that looked brand new.If you don't want to pour money into it just solder new caps temporarily (little solder, don't cut the legs). If it won't work you can remove them for something else.

author: chartle
author_rank: Contributor
timestamp: March 18, 2013, 03:47:13 pm
content: My biggest issue now is getting them out. Everything is really packed in there and they then squirted some silicone gunk around everything to I guess keep things from either shorting or maybe shock resistance. It looks like someone packed old chewing gum around it. I think you can even see here the taller one in the middle is just not right.

author: chartle
author_rank: Contributor
timestamp: March 18, 2013, 03:53:04 pm
content: I should have done some googling first look what I found.http://www.fixya.com/support/t2327065-power_supply_fail_dve_dso_142lThey point to the large cap and few others as the ones that are probably bad.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: March 18, 2013, 03:58:33 pm
content: You can use a xacto knife to cut that white glue out. Just be carefull. Or just wick the solder off the leads and twist that cap out. Once the big one is out of the way the smaller ones should be a breeze to remove. Good find on google btw.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: March 18, 2013, 04:00:54 pm
content: Quote from: KuchateK on March 18, 2013, 03:11:39 pmI do that quite often myself. Since I repair vintage gear that has been a habit of mine for years. Depending if the cap is shorted though, then it does not work.

author: chartle
author_rank: Contributor
timestamp: March 18, 2013, 04:14:23 pm
content: Quote from: Radio Tech on March 18, 2013, 03:58:33 pmI now remember when I was researching this that that model number of PS popped up. I can't seem to find the 47uf cap that are talking about the two in the front are 470 uF. Once I get the big guy out of there I should be able to work it out.

author: chartle
author_rank: Contributor
timestamp: March 18, 2013, 05:37:52 pm
content: OK a picture of what I'm up against on the other side of the board (really thought I posted this) and a "well theres your problem" pic.Here is what I found underneath.If I need to replace the two smaller 47uF caps in the front I have to deal with this mess.And here is the "well theres your problem" pic. When I was putting away the lid I found this. Capacitor guts sprayed right above the big blown cap.