Crackling and popping on my left channel

[Ty_Bower]

...surface contamination from crappy flux or other foreign substances. I use a stiff toothbrush and acetone to clean all the gorp off the board after I'm through soldering...

I'm a bozo, and was too lazy to clean the flux off a board before I started playing with it. Now the amp has run for many hours and all the flux seems to be baked on. I tried using Zippo fluid to clean it off, which usually works very well for me, but no joy.

Can baked on flux be cleaned off? I thought if the heat of soldering didn't "set" it, I'd be OK waiting til later. Guess I was wrong...

[WA4SWJ]

Hi Ty,

In commercial wave soldering operations that use rosin as the active element, the flux solvent used is isopropyl alcohol (rubbing alcohol). It's widely available. Use that and scrub with a toothbrush and it should come off.

I'm not convinced that flux residue would cause this noise problem, but you never know.

Regards,

[Ty_Bower]

I've tried IPA (>90%) and while it does remove a lot of the flux (if the solder joint is fresh), it also seems to leave a greasy residue that smears around the circuit board. Zippo fluid is probably dangerous, but really seems to clean well and leaves nothing behind. At least, it cleans well on newly soldered joints.

I'll have another go with the IPA. I'm not experiencing any noise problems, as reported by the original poster. I just don't want someone to look at my soldering job someday and comment on what lousy work I did. Especially if that someone is going to be me. Yellow_Light_Colorz_PDT_09

[crispycircuit]

With all these "spot on" repair ideas I'm surprised it still haunts you?? After doing all the above aproches I have one more step I take. I take 220 wet or dry sandpaper and buff up the tube pins crosswise. This removes any film etc. .. and leaves a rough finish so that when the tube is installed it digs into the socket contacts. Works great on old gear that's been sitting. Or old tubes with filthy pins....... Cheers!

[mesherm]

Commercial flux remover that we use , sold by Vishay/Measurements Group for strain gage work is 50% IPA and 50% toluene. I make a few ounces at a time for home use. Works good on non water-based flux.

[EWBrown]

IPA - India Pale Ale ? Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_02 Yellow_Light_Colorz_PDT_06 Yellow_Light_Colorz_PDT_09

That would better applied to the listener, and not to the circiut board Yellow_Light_Colorz_PDT_08 Yellow_Light_Colorz_PDT_03

For the baked on, caked on flux, sometimes just carefully picking it off with a small flat blade screwdriver works best, as the flux has lost any liquid or "plastic" properties and has become something resembling dried varnish. Picking it off also eliminates creating more flux slime which can get spread around the board, in the process of trying to remove it. Just go slow and don't dig too deep...

If you do elect to use any of the liquid flux solvents, just make sure to keep it away from the working side of the bias and NFB trimpots, else they may go open, or change the internmal resistance. (been there, done that)

/ed B

[TomMcNally]

I'd agree with crispy ... dirty tube pins or sockets are more likely
to cause problems than flux in an amp. Wiggling the tubes around
will find the offender. Out of about 40 amps I sold on eBay - the
only one that came back was a 6T9 with a NOS Compactron socket
with a dirty pin. Found and cleaned it and retensioned it and it's
been fine.

... tom