Question about substituting components

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tonefloat
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Re: Question about substituting components

Post by tonefloat » Mon Jun 15, 2020 3:55 am

Dear all,

Thanks again for your tips here and Jay, for the pm's.

Last week I built a some beginner kits to practice my soldering technique; Thonk 'AT-AT-AT' and a Music Thing Modular 'Startup' – which both went neatly and successfully.

Yesterday I made a start on the Hex Mutant Hi-Hat and am half way through with all resistors and film & ceramic caps + IC sockets on - soldering continuing to well I think - looks neat anyway.

One thing that is bugging me though as regarding the PCB cleanliness after soldiering; Before starting work I followed advice here on cleaning the boards as they had been sat for 4 years (safely wrapped up I would add). So I cleaned the PCBs with fine grit pumice powder and water which gave they nice light scrubbing and all the pads came up shiny and mildly etched or 'keyed'. Then I gave them a good rinse off and then quick clean in DI water. Finally I wiped them down with 90% IPA (not beer, Isopropyl obvs.... though I had some 7% IPA beer on the go too...) and some q-tips and left to dry for a bit in the sun.The soldering went like a dream after that and everything was looking tip-top with nice shiny joints - albeit covered in flux from the rosin cored solder which brings me onto my problem..

After soldering all the resistors I thought it would probably be a good idea to clean the boards up a bit before creating 'hard to reach' nooks and crannies but populating and soldering the rest of the components. I thought 90% IPA and tooth brush would do it, so dipping the brush into the IPA and scrubbing front and back seemed to do the trick - however as it dried out a bit it was clear that it had sort of left the flux/gunk smeared around in finer sort of film, which was also a bit 'tacky' to the touch.

I left it to dry a bit and then gave it another going over as I had read that it needs a few attempts to fully clean.

Slightly concerned by lack of a perfect clean I gave it a rinse and very light scrub with a bit of pumice powder and DI water before drying and dabbing with IPA again. I would say it cleaned it up better but that there is still remnants of the rosin/gunk around the pads a bit and the joints maybe are not as shiny as the fresh joints I did following when I put the IC's and film, ceramic caps on.

I have not attempted to clean the caps and IC's yet and you will see from the pics that there is a slight shininess differential between the new and older ('cleaned') joints around the resistors.

Note: I also reflowed a few resistor joints following the above.

I would say it doesn't look bad but also is has not come up how I thought it would after the IPA cleanse and wondering if a.) I have messed it up and b.) if I should have or should now use something like a flux remover in aerosol format such as https://uk.rs-online.com/web/p/flux-removers/1908290/ and that would solve it?

Or maybe I am being too fussy?

Any advice would be great.
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KSS
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Re: Question about substituting components

Post by KSS » Mon Jun 15, 2020 3:20 pm

You're not being too fussy. Some rosin fluxes are a 'bear' to remove. Moreso if left uncleaned for any length of time. Commercial flux cleaners are high strength and the alcohol you're using is low strength in comparison. I'd recommend not using any more pumice for cleaning of already soldered joints. Or for gewneral board cleaning. 3M scotchbrite pads are a better alternative. Wouldn't use steel wool either. Ever!. Or sandpaper, which is garnet, aluminum oxide, silicon carbide, or flint.

If-when there's still a smeared or sticky film then you're simply not yet done cleaning the rosin flux from the PCB. In the absence of commercial flux removers, 90+% alcohol, a toothrbrush and effort give the best results. Yes, sometimes it's a PITA.

The rest of what you've described is par for the course. Welcome to SDIY.

That's why MOTM kits used two types of solder and the first needed regular washing. it was designed to be easy to wash, but if left on too long the beneficially agressive flux caused problems. Later in the build when parts were mounted which precluded continued water washing, the flux-solder type was changed to no-clean.

I didn't look at the photos full size.

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J3RK
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Re: Question about substituting components

Post by J3RK » Mon Jun 15, 2020 3:58 pm

I'm a little late for this response, but related the resistor debate on the last page: There are a few brands that make 1/4W resistors in the smaller size. Panasonic is one of them. Digikey sells them. There are more too, but I can't think of them off the top of my head. Just thought I'd mention that you'll occasionally see them, and they are fine to use.
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emmaker
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Re: Question about substituting components

Post by emmaker » Mon Jun 15, 2020 5:59 pm

tonefloat wrote:
Mon Jun 15, 2020 3:55 am
After soldering all the resistors I thought it would probably be a good idea to clean the boards up a bit before creating 'hard to reach' nooks and crannies but populating and soldering the rest of the components. I thought 90% IPA and tooth brush would do it, so dipping the brush into the IPA and scrubbing front and back seemed to do the trick - however as it dried out a bit it was clear that it had sort of left the flux/gunk smeared around in finer sort of film, which was also a bit 'tacky' to the touch.

I left it to dry a bit and then gave it another going over as I had read that it needs a few attempts to fully clean.

Slightly concerned by lack of a perfect clean I gave it a rinse and very light scrub with a bit of pumice powder and DI water before drying and dabbing with IPA again. I would say it cleaned it up better but that there is still remnants of the rosin/gunk around the pads a bit and the joints maybe are not as shiny as the fresh joints I did following when I put the IC's and film, ceramic caps on.
Probably the easiest solution would be use water soluble flux on parts that can be washed and clean off with water (check component data sheets if in question). Couple of things with water soluble flux. First you do not want it to sit on a board for long, not more than 3-4 hours (optimal time is less than 1 hr) and second wash both sides of the board. The flux is very corrosive and that is why you want to wash both sides since some will wick/leach from the solder side to the top. There are videos on YouTube on this.

With rosin flux and IPA all you doing is diluting/melting the flux and spreading it over the board. Here what you want to do is put some IPA on and scrub with a brush, but more IPA on to keep the rosin suspended in the IPA and take a Kimwipe and wick up the IPA. Since the flux is suspended in the IPA it will be wicked up with the IPA. It might take a couple of tries to get a clean board.

Unless you doing things with sensitive capacitors (S/H cap and VCO timing caps), high impedance, high gain or high frequency leaving the flux on (rosin or no clean, NOT WATER SOLUBLE) is OK.

Jay S.

KSS
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Re: Question about substituting components

Post by KSS » Mon Jun 15, 2020 6:20 pm

emmaker wrote:Unless you doing things with sensitive capacitors (S/H cap and VCO timing caps), high impedance, high gain or high frequency leaving the flux on (rosin or no clean, NOT WATER SOLUBLE) is OK.
Leaving rosin on is *not* okay. Although it was done far too often on vintage synths, it's also one of the easiest and most effective ways to fix an old one acting strange. Simply clean the old flux off the PCBs.

Rosin flux tends to catch and hold crud including metallics and salts that make for high impendance -and sometimes quite low impedance!- paths where none should be. There's a reason no-clean was invented and offered!

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emmaker
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Re: Question about substituting components

Post by emmaker » Mon Jun 15, 2020 6:36 pm

KSS wrote:
Mon Jun 15, 2020 6:20 pm
emmaker wrote:Unless you doing things with sensitive capacitors (S/H cap and VCO timing caps), high impedance, high gain or high frequency leaving the flux on (rosin or no clean, NOT WATER SOLUBLE) is OK.
Leaving rosin on is *not* okay. Although it was done far too often on vintage synths, it's also one of the easiest and most effective ways to fix an old one acting strange. Simply clean the old flux off the PCBs.

Rosin flux tends to catch and hold crud including metallics and salts that make for high impendance -and sometimes quite low impedance!- paths where none should be. There's a reason no-clean was invented and offered!
Probably a good idea.

I have 6 pieces of gear that are between 50-60 years old that still work (OK one I haven't turned on in 6 years, it did work last time I turned it on) that were done with rosin flux. 4 are terminal strips with point to point and 2 are PCBs.

Happy soldering.
Jay S.

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tonefloat
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Re: Question about substituting components

Post by tonefloat » Tue Jun 16, 2020 8:12 am

Thanks guys - Kimwipes on order and elbow grease at the ready.

With regards 'no clean' solder - what is the best stuff to buy - what are people here using? I posted above I am using 30/60 tin/lead - is there a no clean version of this that is a safe bet - I was looking at this;

https://www.somersetsolders.com/tin-lea ... HYQAvD_BwE

Seems ok?

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EATyourGUITAR
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Re: Question about substituting components

Post by EATyourGUITAR » Tue Jun 16, 2020 8:49 am

cleaning directions are right there on the website. I use leaded at home. the only thing you can't do with leaded flux is repair of lead free boards.
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tonefloat
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Re: Question about substituting components

Post by tonefloat » Wed Jun 17, 2020 4:54 am

Update::

Seemed to all go together quite well - albeit still some rosin cleaning needed which may or may not have contributed to the following sorry scene; plugged in the module - no LED activity, 1-2 secs later a dreaded pop and a puff of grey smoke - powered down straight away.

On first inspection I can see a blown 220uF cap on the + side (left hand side) of the power header. A closer look this am and I can see that one of the pins in the header on the + side looks to be standing tall off the board/taller than the other pins (unclear if this pin is not in contact with the pad beneath entirely though as solder covering - though I don't know now how I didn't spot that the pin in question was not poking out identical to the others on the blind side).

I am hoping that the issue is just with the header and the cap (which I do have some spares of both) and that I have not ruined the module via impatience and lack of thoroughness..... :doh: :confused:

I haven't taken apart yet but there doesn't seem to be anything else visually noticeable elsewhere.
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Eloc
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Re: Question about substituting components

Post by Eloc » Wed Jun 17, 2020 8:42 am

I would double check polarity of your power (yes it's a shrouded header, but it could be the wrong way round, or the cable could be wrong etc) and check the polarity of the cap. Electrolytics will pop if you have them the wrong way round, or exceed their voltage rating.

If the header is the correct way round, you should be able to reflow the solder for just that pin and push it further in (not with your finger as it will be hot...) rather than replacing the whole part.

The silkscreen should show where the notch in the plastic part of the header should be. If not, there is a little arrow on the side of the header (to denote pin 1). This should be on the -12V side (and the red stripe on your power cable)

[edit] in fact looking at your earlier photos I can see that the header is the correct way around, but the cap looks to be the wrong way around, which would explain it popping.

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tonefloat
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Re: Question about substituting components

Post by tonefloat » Wed Jun 17, 2020 2:51 pm

Eloc - cap solved it! Cant believe I missed that, thanks - I blame working too late into the night :roll: Another less learned.
Now for testing...

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