January 31, 2020 at 2:47 pm #10413CybercowModerator
RickMurphy – there is no “white powder”. What you are seeing is the result of the audio probe tip scratching the left-over flux (residue) from soldering.
Also, to perfectly honest with a sincere intent towards constructive critique, your soldering technique appears to be quite inconsistent. Some solder points are clearly supplied with solder, while other solder points appear to have NOT been heated enough and the solder just blobbed up around the leads\wires poking thru the PCB. I suggest reflowing the solder, with possibly a touch of additional flux on the solder joints. For instance, note the lack of solder around the diode leads (diodes D3 & D4) on the component side of the PCB.
Once you’ve reflowed the solder, you can use an old toothbrush and rubbing alcohol to remove any excess flux from the solder-side of the PCB. Just let it dry thoroughly before firing it back up after the alcohol cleaning.
Regarding the volume when the clipping diodes are engaged: clipping diodes will limit the signal to a maximum of the Fvd of the clipping diodes. Silicon typically has a Vfd of 0.78v to about 2.5v – depending on what diodes are used. (1N914 are at about 0.78v and some LEDs have a Fvd anywhere from 0.9v to 2.5v depending on the specific diode used. So when the clipping diode switch is in the center position, there should be no clipping diode engaged. (At least, based on the schematic.)February 1, 2020 at 6:35 pm #10496rickmurphyParticipant
Thanks much for your constructive critique. I am new to soldering and I look forward to learning from your suggestions.
While I followed the guides in using a fine conical tip, I found that the tip did not heat well unless I touched it 1/8 of an inch or so above the pad, then I struggled to get the solder down to the pad. I have a narrow chisel tip that seems to heat the components better than the fine conical tip. Can I use that instead?
I plan to ask a few follow up questions about the clipping diodes after I re-flow the solder and cleaned the board.
Thanks again for your help.February 1, 2020 at 7:08 pm #10497BarryKeymaster
Do you tin the tip after every 5 to 10 solder points and clean the tip using a metal scouring pad etc between every couple? The tip should be nice and shiny for even heat distribution.
I have been using the same exact conical tip now (like in the photo) for 5 years and it still looks great.
You can tin with solder but I like the stuff below and it lasts forever.
Heat the pad and component lead simultaneously for a few seconds (longer with ground pads) before applying solder to the pad and tip.February 2, 2020 at 11:37 am #10551rickmurphyParticipant
Barry, thank you for taking the time to provide this advice.
Yes. I am very disciplined in cleaning the tip. I have a can of tin and use it on the tip.
What I did wrong based on the diagram was to touch the solder to the tip-side of the work rather than touch the other side. What I observed was the pad had not sufficiently heated and the solder did not flow from the tip to the pad.
When I reflow the solder I will experiment with 1) a narrow chisel tip which may provide a larger surface area to transfer more heat to the pad; and 2) increasing the nominal heat displayed on the soldering station from 750 to 850. The nominal heat on the display may not be accurate.
Thanks again for your advice. I hope to report back later in the week.
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