Randy Day wrote in message
.. .
In article ,
says...
[snip]
As for the failed C pad
This pad had survived original soldering, my first desolder and resolder
and
came away with second desoldering leaving bare board where the pad was.
I expected to see copper colour after scraping into the white circle but
only silver colour of solder seen - no copper pad there ever? so thin it
disolved ? when I desoldered/resoldered initially there was a normal pad
of
solder there
Most likely the pad came away with the soldering
iron tip on the last reflow. It's probably
sitting on your tip cleaning sponge with all the
flux residue, or in your vacuum desoldering tool.
It's very easy to do and easy to miss.
Anytime you reflow a pad more than once, you have
an increased likelihood that this will happen.
The copper adhesive isn't intended to be melted
over and over...
the pa and ps share the same hs so I put the 2 caps on the track side of the
board, mainly so easier to temporary change the timing 100uF to 1uF if
necessary.
the 4.7uF smooths the rectified ac for power-off sensing but with it
intermittant contact , when that IC pin goes less than 0.7V in next mains
cycle, it triggered muting.
Anyway second time of desoldering the small cap, the pad came away, with the
usual few grams of force when blob molten. As a wired C , i desoldered with
normal soldering iron.
Amp back with owner now.