Step 26. -
Clean the PCB!
It's a little unusual to detail cleaning the PCB like this, but remember - HIGH VOLTAGE. There's more force behind higher voltage and it will "jump" across connections more readily than the typical SS or hybrid amps that are built on a PCB. So, IMHO, cleanliness is part of the safety. You don't want any of that old flux and soldering dirt to create enough of a connection that might encourage the voltage to arc across a set of leads. So, we're going to clean this PCB well and show you how to do it easily and cheaply.
Below we see the PCB with my essential tools for cleaning:
Next to the PCB we see a small butter bowl and a toothbrush. Next to that is a bottle of the alcohol that I use for cleaning. This is 91%, but is less than a dollar at Walmart (last time I checked). A quart will last you a long time. I've tried several chemicals that they make supposedly specifically for solder flux, but none of them clean as well as 91% isopropyl and most of the other chemicals emit vapors so bad you need to use them outdoors. So, I stick with the alcohol.
Anyway, I pour an inch or so into the butter bowl and use the toothbrush to apply the alcohol across the entire PCB. Use the brush to scrub the places where the flux is really thick:
The alcohol dissolves most of the flux right away. However, something a lot of people don't mention is that the dissolved flux-alcohol mixture doesn't go anywhere unless you try to drip all of it off of one side of the PCB. That's not a very good strategy, so I use paper towels to pat up the dissolved mixture:
So we're done, right? NO! Take a look at this:
That white stuff you see is the dried-up flux that was deposited after the alcohol evaporated. So that means a single dousing of the alcohol, toothbrush, and paper towel didn't get it all.
In reality, it takes several rinses. It took me six times to get the PCB to an acceptable condition:
That sounds like a lot, but honestly, it was probably 15 minutes or less. The alcohol evaporates so quickly - especially when using the paper towel - that multiple rinses go very quickly. In the pic above, you may be able to still spot some white stuff around the solder joints, but all-in-all, it's pretty clean and good enough for me.