2 Jun
2012
2 Jun
'12
11:27 a.m.
A couple of months ago I picked up a Terak, in pieces. I'm now working
on putting it back together as well as I can; the power supply has three
large capacitors that are visibly leaky (i.e. there's crud coming out
the ends) so I would like to replace them before I go any further.
Thing is, I've never run into a capacitor quite like this -- it's a
radial capacitor, about 1" in diameter, and about 4" long, but there are
pairs of terminals on both ends (i.e. a "+" and "-" terminal on both
ends).
It's marked as follows:
MALLORY
1300 MF 75V 105C
QLA132U075N3L
235-7838
I considered that this might actually contain two capacitors in one can
(as I've seen in some old radios & TVs I've worked on), but the markings
on the can don't seem to indicate that this is the case, and further it
looks like (based on probing with my DVM) the power supply board is
wired such that the "+" on one side is the same circuit as the "+" on
the other. (I don't have a schematic to confirm this, and I haven't yet
pulled the whole power supply PCB out to validate this.) Additionally,
after removing the capacitor from the circuit, there's continuity (w/ no
apparent resistance) between the "+" terminals on either end of the
capacitor. So it -looks- like this is just a single 1300uF capacitor,
but I'm curious as to why there are terminals at both ends...
There are 2 reasons I can quickly think of for having 2 terminals for
each side of the capacitor.
Firslty, it could result lower inductace in the circuit, or perhaps no
_common_ inductance between 2 circuits (charge and discharge ;-))
connected to the capacitor.
Secondly, it could be a safety feature If the 2 equivalent termianls are
conencted to differnet points in the cirucit, then if either wire becmes
disconencted, it would open the entire circuit, whereas if the 2 wires
were conencted as a 'T' to one terminal, then if the termianl fiailed the
2 wires might still be conencvted to each other but not to the capacitor.
I think the first is more likely here.
-tony