20 Jul
2015
20 Jul
'15
11:06 p.m.
On Sun, 19 Jul 2015, dwight wrote:
I have rarely seen static damage to electronic parts.
I can imagine that
if I were in Nevada during winter time, I might see more. There were
times when, even with a key to be the discharge point that my arm still
jumped.
On parts, the ones I've seen that I could definitely attribute to static
were, VFets with no zener input protection and the CMOS parts, 4051,
4052 and 4053.
The VFets were killed with soldering irons that someone cut the ground
wires so I couldn't really say it was static in the normal sense.
I doubt any power supply could ever be damage from a discharge to a
output lead. The ratios of capacitance is too different. The human body
just doesn't have enough capacitance to mean anything to a power supply
filter capacitor.
Now, if your talking lighting as the source of static, I've even seen
those static protection parts blown off boards.
Now that is static damage!
Tinker Dwight
Oddly enough, I have a Sangean ATS-803A (Radioshack DX-440) receiver on my
bench right now which has static electricity damage. They used two Sony
2SK152 JFETs (long since discontinued and virtually impossible to source)
which can be damaged by static electricity merely by touching the
telescoping antenna. I've replaced the two 2SK152 with Fairchild J113
JFETs and retrofitted a pair of inverse-paralleled 1N4148 diodes just
before the antenna selection switch (between ground and the switched side
of the external antenna jack) to help prevent future damage to the
replacement JFETs. The receiver still isn't working quite right just yet
though. It currently works fine on broadcast AM up to 1620KHz (internal
loopstick antenna) and broadcast FM with the external telescoping antenna,
but at 1621KHz and above in AM mode, the set is totally deaf. It is
supposed to use the external telescoping antenna for AM operation above
1620KHz, but there is still a faulty component somewhere in that portion
of the circuit.