PSU disaster waiting to happen? - Page 1
Forum section: electronics / general

author: rvmeush
author_rank: Contributor
timestamp: March 20, 2013, 12:57:00 pm
content: I purchased a used Instek GPS-3030DD power supply recently. I got an Instek model because it seemed to get generally good quality reviews compared to other similar inexpensive supplies. I turned it on to do a quick check and it seemed to be working. Following Dave's lead I decided to open it up and have a look at the quality of the construction. It wasn't built as sturdily as I would have liked but the electronics components seemed okay. Then I happened to notice the placement of the main circuit board and that it was only held in place by two screws - so it was subject to some flexing. I was shocked to see one component lead precariously close to the metal chasis (see picture). Now I'm wondering if I should keep this supply or return it. I don't see any indications of arcing. I don't know exactly what that pin is connected to, but I'm pretty sure it's not a ground connection. I'd like to know if I should just assume there was no damage because the power supply seemed to work okay, or are there some other tests I need to make before deciding to keep it. Obviously I'd put in some insulating material to keep the pin from shorting to the chasis if I kept it. Any thoughts would be welcome.

author: c4757p
author_rank: Super Contributor
timestamp: March 20, 2013, 01:13:02 pm
content: Well, that is some really shitty, negligent design there. Still, no need for insulation, just clip it. It's long.Quote from: rvmeush on March 20, 2013, 12:57:00 pmI would be profoundly worried if a 30V power supply was arcing.

author: AndrejaKo
author_rank: Frequent Contributor
timestamp: March 20, 2013, 01:16:40 pm
content: My advice too would be to clip or at least bend the lead. The lead looks sharp-ish, so I fear that if insulating material is used, it would eventually pierce it due to already mentioned board flex.

author: ignator
author_rank: Regular Contributor
timestamp: March 20, 2013, 01:29:40 pm
content: Quote from: c4757p on March 20, 2013, 01:13:02 pmI'm not aware of any good design companies, that have a 3D rendering of the PWB laid out assembly, that then is inserted into the 3D mechanical model to do a fit check. I bet there was circuit card assembly instructions of Z-top Z-bottom that were ignored by production even if engineering had this observed possible lead length protrusion, in the original proto-type. Then again, it may be a ground connection, and is not a worry.Until it's a field problem, or a factory can't ship problem they will keep making it that way. I just assume now that everything has packaging errors.

author: c4757p
author_rank: Super Contributor
timestamp: March 20, 2013, 01:35:08 pm
content: How hard is it to just not put things above the metal? It's not a solid plate, it's just an arm. Surely they could have squeezed that lead a couple millimeters over?Quote from: ignator on March 20, 2013, 01:29:40 pmI know that anything involving "documentation" is totally unheard of today, but personally, if I put a grounded lead near a grounded chassis, I'd at least slap a ground symbol next to it so nobody sees it and thinks it's a problem. Not that anybody has any pride in their designs any more, though. Electronics today is infected with "who cares, it works".

author: Fraser
author_rank: Super Contributor
timestamp: March 21, 2013, 07:38:07 pm
content: My advice is to write to GW Instek. I have had very good experiences with telling a manufacturer about a design flaw. Freebies have often resulted !Fraser

author: mbqwerty
author_rank: Newbie
timestamp: March 22, 2013, 12:19:48 am
content: Quote from: Aurora on March 21, 2013, 07:38:07 pmI have also found that happens with customer service feedback.

author: rvmeush
author_rank: Contributor
timestamp: March 22, 2013, 01:50:30 am
content: I decided to disassemble the power supply to see if anything else looked odd. I discovered that there was a plastic guide at the bottom of the case which was supposed to hold the circuit board in place (see attached picture). With the board in this guide the component leads that I was concerned about were held away from the case - so they wouldn't be close enough to short to the case. For some reason the board was not in the guide. The overall rigidity of the case isn't particularly good, but it would be nice if there was some more foolproof way of holding the board in place. So, I guess Instek wasn't negligent after all in their construction technique.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 23, 2013, 07:47:56 am
content: This sort of thing happens in the best of families.A HP Noise & Distortion Test set at one of my workplaces had a rear panel mounted mains fuseholder with its (uninsulated) end withina few millimetres of an internal shield.This plate was not mounted very securely,& could flex,with the definite possibility of shorting the mains active to earth/chassis.Fix?Glued a piece of fairly heavy perspex on the shield!Then there was the Marconi Sideband Analyser,where a loose spare nut lodged under a tagstrip,& would on odd occasions short out the 300v Dc HT line.Or,again Margoni ,Chroma/Luma Gain & delay test set,where they squashed the wiring form between the front switch bank & the PCB under the switch.Or,the Sony BVM1410 Picture monitor with the 240V & 120V Degaussing circuit PTC thermistors transposed.The 120V one did last 10+ years,but when it did go bang it went up like fireworks night.Easy fix,as there was the correct spare----------sitting in the wrong position on the board!

author: Rodville
author_rank: Contributor
timestamp: March 23, 2013, 07:21:58 pm
content: That first picture looks scary. Especially with the two components that are just under the rail that look like they can contact the rail.

author: rvmeush
author_rank: Contributor
timestamp: March 23, 2013, 08:13:44 pm
content: You can't see it in the first picture but there was a small distance between those first two leads and the rail. The lead that was closest was the one that can be seen the best.

author: Fezder
author_rank: Regular Contributor
timestamp: April 11, 2013, 07:14:11 am
content: woa, that sure looks dangerous :S....

author: KJDS
author_rank: Super Contributor
timestamp: April 11, 2013, 10:51:40 am
content: Quote from: ignator on March 20, 2013, 01:29:40 pmI've worked on a few projects where that has happened. It's just about essential if you're designing a phone or something else similarly small and I've seen it done on large, complex projects too.