I'm guessing this is probably one of those issues where there are strong feelings either way and no firm conclusions to be reached based on facts, but if one were to reflow all or many joints on an old amplifier (for whatever insane reason), are we talking about just heating up the existing solder to a molten state or are we talking about adding a bit of new solder to the joint in the process? Clearly, properly cleaning by removing old solder and providing all new solder on a mass basis would be a ton of work and result in lifted pads meaning ever more work (like home improvement projects, at least in my house) and would not really be practical.
Are there any possible benefits to doing something like this to an older, much used amp?
Are there any possible benefits to doing something like this to an older, much used amp?
Resoldering old joints is usually a measure of desperation when nothing else fixes a problem. Sometimes it even cures the problem but mostly not. I say, if it ain't broke, don't fix it. Now, if there are obvious cold solder joints or leads that didn't wick well, sure, go ahead and touch 'em up. You usually have to add flux. Adding solder works because you're adding flux from the solder, but it's easy to get too much solder that you then have to suck or wick up. I'd never routinely resolder a board- it just contributes to what I call "technician blight" where you look inside something and say, "oh crap, somebody's been messing around in here". I hate to get equipment like that. 😡
When reflowing a solder joint, you need to add flux. You can either get a flux pen or other flux dispenser and add a drop before reflowing the cold solder joint or you can use the easier approach of just adding a little fresh solder to the joint. In either case, if the solder doesn't flow well when you reheat the joint, you need to remove the solder (use solder wick or a solder sucker) and start over.
But if it ain't broken, don't fix it.
~Tom
But if it ain't broken, don't fix it.
~Tom
1st rule - if it ain't broke don't fix it. OTOH - IF a solder joint looks unfit due to corrosion - cold solder joint - excessive heat - improperly soldered then you might want to consider a resoldering. I apply a drop of liquid flux and reheat the joint - sometimes a dab of new solder if needed. Wires that have been exposed to excessive heat over the years (same thing for PWB traces and eyelets) can become very brittle and easily broken and at that point you will need to decide on just how far you wish to pursue the project. A complete rewire of a unit is time consuming and requires a mid to high level set of soldering skills and tools. If you only mess around with a few solder joints that really need a bit of TLC you should be ok assuming that you have the tools and solder knowledge. BTW - some of those caps can hold a charge for quiet a good amount of time - remember to discharge 'em (ie - not via yourself!).
There are a number of reports of cold joints developing on STK chips on the silver Pioneers, that is the extent to which I would attempt the technique. There are also some who claim improved performance after widespread reflow, but I'm skeptical of that claim.
A "cold" solder joint is cold from the moment that it is created - it does not become a cold solder joint over time. Usually has a grainy appearance to the eye and if they operate at all then they can indeed fail after some amount of time as thermal expansion and contraction of the joint (due to temp variation from cold to hot etc.) will cause them fracture and fail. It can be a real bugger to find 'em because sometimes the failure is intermittent and will fail due to heat or vibration. A little touch up with a hot tip and some flux should put things right.
I think the term "cold" solder joint is often used incorrectly.
What I've seen is more like micro cracks around the soldered pins and leads of components caused by thermal cycling fatigue. You will mostly see these in hot running gear and its first symptoms are noticed with intermittent problems. Most of these connection failures will be with larger components or sub-circuit assys that are factory soldered on PCBs and then screwed down later into the chassis or heat sinks. Components with PCB to chassis interfaces like switches, pots, RCAs, connectors, power transistors, etc seem to be likely places to inspect. Quite a few of these failures could be avoided with either more stain relief, tolerance, and different assembly procedures. A good re-flow with these mechanically stressed solder joints after the PCB and mountings are tightened down goes along way in helping these solder micro crack lead problems. Reflow the problem area joints in-mass either before or after more failures are detected. Alot of these issues could be avoided with good ventilation too.
What I've seen is more like micro cracks around the soldered pins and leads of components caused by thermal cycling fatigue. You will mostly see these in hot running gear and its first symptoms are noticed with intermittent problems. Most of these connection failures will be with larger components or sub-circuit assys that are factory soldered on PCBs and then screwed down later into the chassis or heat sinks. Components with PCB to chassis interfaces like switches, pots, RCAs, connectors, power transistors, etc seem to be likely places to inspect. Quite a few of these failures could be avoided with either more stain relief, tolerance, and different assembly procedures. A good re-flow with these mechanically stressed solder joints after the PCB and mountings are tightened down goes along way in helping these solder micro crack lead problems. Reflow the problem area joints in-mass either before or after more failures are detected. Alot of these issues could be avoided with good ventilation too.
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Output resistors and those under browned-out resistors are also a prime suspect for cracks, if the components themselves are OK. Even ground pads, the ones that connect a board ground to a metal tab or chassis using screw tension, sometimes wear under the pressure.
And sometimes you get gear that has been mercilessly and badly reflowed by other service personnel that makes you want to drown yourself. Large untidy lumps on every joint, with enough flux for sixteen supercomputers.
I usually *have* to do it all over again as someone who reflows without discretion has usually overlooked something else. I use a wick to drain the lumpy bits off, then apply a bit of solder from a fresh spool (basically, resolder the joint).
More than amplifiers though, TVs and monitors may benefit, specially those that have cold start issues. A light brush over the PCB and a nice blowing from a hot air station will sometimes revive an old beast.
Unless you do have issues, I don't think resoldering is worth it. However, I have recapped some vintage amplifiers, often with spectacular results and would think it could help even if the amp isn't actually broken.
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