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Made by Monkeys

Sometimes All You Need Is a Little More Solder

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Critic
User Rank
Platinum
Good Luck you had
Critic   7/6/2015 11:37:03 AM
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Good job of troubleshooting, Kevin.  So solar arrays really do require maintenance?

patb2009
User Rank
Gold
surge supression
patb2009   7/6/2015 6:23:04 PM
tell us about your surge supression system, i'm about to do a 4 KW solar array.

rollywind
User Rank
Iron
What type of solder did you use?
rollywind   7/7/2015 9:20:39 AM
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Unfortunately, IMHO, we are now using an inferior solder to boot. I've found more problems moving to lead free solders than any other combined. In my career solderflow is difficult to maintain at the best of times. Glad you found the problem!

YJ77
User Rank
Gold
Re: What type of solder did you use?
YJ77   7/7/2015 9:31:55 AM
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Lead free solders are the downfall of many electronic assemblies.  The service life of new assemblies is much shorter than earlier products.  High volume electronics are now 5 year designs rather than 20 year designs, and replacement with a "new" 5 year part is often the only option.

Larry M
User Rank
Platinum
Re: What type of solder did you use?
Larry M   7/7/2015 10:08:05 AM
I trust that when Kevin "added a little more solder" he had the good sense to use tin-lead solder, to alloy a little lead into the joints.

splatticus
User Rank
Bronze
To make sure repair of monkey fab is not monkey do
splatticus   7/8/2015 9:02:21 AM
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Adding Sn/Pb solder to most types of Pb-free creates an alloy that can only form the equivalent of a cold joint. If the original type is unknown, best to just knock and suck as much as possible of the original solder out and replace it with Sn/Pb. 

The switch to Pb-free has made proper repairs more difficult/unliikely. We pretty much need a mini-sized beta backscatter device to assay the original solder, first. Hmm, actually, just checked, and amazingly, there is at least one, from wwwDOTupaDOTcom/indexDOTphp. I'll bet it costs a fortune.

Noodling on it a bit more, all we really need is a way of telling if, in particular, there's any lead in it, since this is what you want to avoid adding to a lead-free solder. A lousy wave soldering job is tell-tale of course, but not definitive. Found a simple, qualitiative detection method, based on sodium rhodizonate and vinegar: wwwDOThome-health-chemistryDOTcom/Lead-DetectionDOThtml They sell a kit, and Sigma Aldrich has 5g bottles of the reagent for a similar price. 

Larry M
User Rank
Platinum
Re: To make sure repair of monkey fab is not monkey do
Larry M   7/8/2015 9:47:19 AM
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Thanks for the useful information!

stumichaels
User Rank
Iron
A lot more solder
stumichaels   7/8/2015 10:41:52 AM
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I had a '75 T'Bird.  After about 5 years, it began stalling occassionally, usually at highway speeds.  Generally, I was able to restart it by shifting into neutral and turning the key to start.  I eventually traced it to the ignition module.  I brought the module to work and the process engineer was able to depot the module whereupon many of the components fell off the printed circuit board.  Examination of the solder joints showed that the only good joints were at the wires attached to the module.  I'm sure these wired were hand soldered.  All the remaining joints showed little solder and no fillets.


The replacement module failed two years later the same way.  I didn't bother to depot this module since it was likely the same problem.

ferd
User Rank
Gold
missing solder on new boards
ferd   7/8/2015 11:13:03 AM
Reminds me of a similar encounter I had when I was a technician troubleshooting fire alarm systems.  A customer had an intermittent problem with his system going in and out of "trouble" mode.  After finding no problems with any sensing or alarm circuits I became suspicious of the monitor board.  But then we noticed that the problem would occur on sunny days at around 3:00 in the afternoon - when direct sunlight would strike the main panel.  The sunlight shined directly on one of the sensing circuit boards, and after pulling it and examining it we found through-hole joints with little solder, and even a few with no solder!  This was a brand new replacement board that we'd substituted while troubleshooting; I looked at the original board and found it also had missing solder.

 

Soldered all of the joints and put it back in – worked fine.  Looked at the remaining boards and ended up fixing joints on the rest of them too.  Decided that the sunlight heated a joint just enough that a component lead moved (expanded) enough to break the circuit.

 

BTW, thought we were done but several months later (now in the winter) the intermittent "trouble" mode came back.  Turned out to be bad solder joints on the monitor card itself.  Had overlooked it when we found problems with the sensing boards.

 

Lessons learned:  do not trust new replacement parts.  They can be as bad as the old parts.  Also, if you find bad joints on one board of a system you'd best check all of the other boards in the system.

ragtoplvr
User Rank
Gold
Where's the savings?
ragtoplvr   7/9/2015 10:32:33 AM
It is hard enough for a solar array to make money.  Using the $.10 per KW/Hr replacing that inverter would cost over 3000KW, more like 6000 to 10000KW if you had to use a technician.  Where is the savings?   This is a reason I am in favor of KISS on these arrays and many other things.

 

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