Perils of "spares or repair" - Page 1
Forum section: electronics / repair

author: grumpydoc
author_rank: Super Contributor
timestamp: March 03, 2012, 06:10:31 pm
content: I don't mind buying stuff that needs repair - but would prefer if a gorilla with a soldering iron hadn't beaten me inside.This from a 0-30V 20A bench PSU sold by the manufacturer as faulty but with the heavy implication that no repair attempts had been made.I suspect one of their engineers tried but that they have a policy of "fix it in N hours or flog it on eBay", he's replaced the 741's that drive the pass transistors but stripped several pads in the process, joy

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 03, 2012, 06:13:11 pm
content: Test gear is certainly one of the more risky "for repair" categories, as it's typically been owned by, or passed through the hands of the sort of people that will be able to fix anything simple!

author: grumpydoc
author_rank: Super Contributor
timestamp: March 03, 2012, 06:17:45 pm
content: You're right, of course, and I do consider that when buying, but it would be nice if they could at least replace a few ICs without knackering the PCB.In this case it looks like it's closer to "...the sort of people thatthinkthey will be able to fix anything simple!"

author: Simon
author_rank: Unknown
timestamp: March 03, 2012, 10:24:05 pm
content: well even I could lift ICs off board when i was a kid and wanted the IC and the board did not get wrecked in the process even though I did not care for the board. A gorilla indeed

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: March 04, 2012, 05:01:39 am
content: This thread is offensive to gorillas.lolWow, that's awful. Best of luck repairing it.

author: FenderBender
author_rank: Super Contributor
timestamp: March 04, 2012, 05:06:59 am
content: I wouldn't bash the guy as much as the PCB. The one there appears to be asupercheap type. You can just tell. I tried repairing a Logitech amplifier board of a similar quality and as hard as I tried- I lifted about 4 pads....and it's not like I have a problem with soldering. I could do 0805s all day.However, if it was made with a better PCB, the fixes probably could have been done better, in my opinion.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 04, 2012, 05:17:37 am
content: Back in the day,CirKits in the UK made PCB repair kits which were very useful for just such a situation.Unfortunately,they were quite costly in Oz,as well as hard to get.That said,I brought a lot of boards back to life when I worked at the TV Station,using them.I found the worst boards were sometimes the neatest,with tiny pads,& undersized holes,which some manufacturers insisted on using in high power parts of Picture Monitors.

author: SeanB
author_rank: Super Contributor
timestamp: March 04, 2012, 02:15:27 pm
content: My repair kit was a bottle of superglue, a few metres of wirewrap wire ( or Cat5 solid core cable nowdays) and a small screwdriver ( 0.8mm diameter) to make the new land, and then solder the new component into place. Superglue then used to hold down the lifted trace and fix the component leads into the hole. Either that or order a 200k replacement board ( and yes, they were 200k each, I did have to order some, the PSU would have made Dave cry at the price, it cost more than Platinum Rhodium alloy mass for mass) and wait a year. Fibreglass board with 4 layers plus, and I was lucky in that most of the time the IC's I was replacing ( SFC2741PM3 oh so often due to offset drift, but could only used the specified part as they were certified) only went to the bottom of the board, and that there were nearby vias if needed on some. I went and bought myself the most expensive soldering iron tip I ever bought, special ordered from RS, the flatpack soldering tip for a Weller station. Bob saw it and asked if he could borrow it, I replied only if I was attached to it. Saved a lot of damage that tip, could remove a flatpack or the TO100 cans easily with it, and it did not lift the fragile copper off those bloody boards.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 04, 2012, 04:59:36 pm
content: Quote from: SeanB on March 04, 2012, 02:15:27 pmEek!

author: SeanB
author_rank: Super Contributor
timestamp: March 04, 2012, 05:49:35 pm
content: Yes, aircraft spares are anything but cheap, especially if they are made from Obsoletium, and are Unobtainium plated to boot.That power supply had a common fault, a failed MC44 diode that would be either open circuit ( good) or short circuit ( charbroiled computer on its way in 2 hours of flying) that was obsolete even when they were new. We used 1N4007's and thinned down the leads a little to get them to fit the holes with some batches. The PSU had fuses, they almost always never blew, the input fuses would survive the meltdown until near the end, when 2 would blow at most. You could smell the fault even before opening the 72 M3 hex screws that held the case hermetic. I bought an electric screwdriver and made a long bit pretty fast, to have the case open in under an hour. I wore out the gearbox on that driver, and bought new gears for it from Black and Decker spares.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 07, 2012, 10:10:07 pm
content: QuoteThanks - turned out to be a duff pass transistor, showing about 30 ohms collector to base both ways - obviously the 6x 2N3055's are in parallel so the bad one was providing base current for the other 5. All fixed now - I just need to work out how to construct a dummy load to test it. I figured out a few high wattage car headlight bulbs wired in series/parallel should give me something that would draw about 20A at 30V. Mind you 600W of halogen lamps is going to be pretty bright!QuoteFair point, except:I have two soldering irons one a cheap temp controlled one and the other a 40W non temp controlled Weller with a very hefty "screwdriver" type bit (yes, I need a better iron). You wouldn't associate the Weller with electronics work but I find it does "chunky" stuff better than the temperature controlled iron. As there was a lot of hefty cable for the high current paths soldered directly to the PCB traces (is that common in high current PSUs? can't say I was that impressed) I used the Weller - and, because that was the iron that was hot, I also used it everywhere else and still didn't lift any tracks.

author: T4P
author_rank: Super Contributor
timestamp: March 07, 2012, 10:23:20 pm
content: High power hakko's do the job perfectly .It's all about thermal capacity , if you haven't seen Dave's soldering tips yet .

author: grumpydoc
author_rank: Super Contributor
timestamp: March 07, 2012, 10:45:44 pm
content: QuoteIndeed, which is probably why the Weller is better at soldering anything with a bit of mass to it.QuoteI'd love one but my pockets aren't all that deep, also not easy to find in the UK.Does anyone have any suggestions under £100 and readily available in the UK?

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: March 08, 2012, 05:50:41 am
content: Quote from: grumpydoc on March 07, 2012, 10:45:44 pmBenz-O-Matic (brand name) propane torch kitsused tocome with screw-in tips made for soldering. It looks just like a regular electric soldering iron tip, but with exit holes for the flame, and a broader tip. A plumbing or home improvement supplier should have them, and you should be able to obtain the tip, valve, and propane for WAY less than your limit. Here, I often see good, US-made kits with all of that for less than $30.Of course, there are butane-fueled soldering irons available too, and they're fairly cheap (in every sense of the word), but they won't have the thermal inertia of the larger propane one.

author: grumpydoc
author_rank: Super Contributor
timestamp: March 08, 2012, 07:44:02 am
content: Sounds a bit meaty for SMD work

author: T4P
author_rank: Super Contributor
timestamp: March 08, 2012, 10:35:22 am
content: Quote from: grumpydoc on March 07, 2012, 10:45:44 pmhttp://labtronix.co.uk/drupal/shop/soldering/898bdplus