electric fence , force field B20, 2007

[N_Cook]

8 pin SMD with blown hole in the casing. Top mark , very indistinct maybe 2
lines
0h963
0h37

maybe very stylised 4 instead of h, logo very indistinct. My first guess is
a 555 but pinning not standard
p3 ground, p8 +12V, pin 1 to a 10uF cap , other end to 0V, p5 tied to p6
goes to speed change pot with also a line from the pot to p1. No obvious
output trace.
Removed the device and internal connections between p2 and 3 presumably
fried , and also p6 and 7
Other device is a 16 pin with ident scraped off or the conformal coating
dissolved off.

In passing , a 8x5x3 mm fuse with bo encapsulation , mainly 2 bare Al plates
with something between. Working order measures 0.18R +/-.01R, marked/punched
in the Al
100
B7L
never seen anything like it before
make/series/value?

[N_Cook]

The fuse is surface mount , I suppose as high current draw, if only
intermittant ,it has to be quite high current, perhaps 10 amp from the 100
marking. Top face 8x5mm bent down the 3 mm over the other plate to one pad
and the other smaller plate , about 6x45mm to the other pad and some thin
material in between

[N_Cook]

of this form, polyswitch
http://www.westfloridacomponents.com/IC523PE05/40A+15V+1.9W+Resettable+SMT+P
olyswitch+Fuse+Tyco+SMD250-2.html
perhaps 10 amp version

[N_Cook]

The main 14 pin SMD has no trace to 12V but p1 goes to this 8 pin SMD which
is connected to 12V so presumably some sort of current or voltage control
requiring 0 and 12V and the pot connection changes the current/V, not the
speed from "Normal" setting to "Turbo" at the top of pot range, and the
output somehow chopped or something from the 12V , smoothed by the 10uF.

[N_Cook]

Those polyswitch resetable fuses may have problems in hot conditions.
Breathing on this one for 5 sec raises the 0.18R to double or so and a
soldering iron barrel switched off and cooled for 2 minutes, laid on it, is
enough to raise to kohm. Alternatively useful highly non linear thermal
sensing elements.

So far have not found a buck boost L-free version of DC to DC converter ,
step down, IC, presumably made variable via use of the pot rather than a
zener. L free version of Maxim MAX758,830,724 or 726 if anyone knows of
something that fits the bill?
This fence is stated to run on 9V as well as 12V battery so I suppose i/p 5
to 15V and output perhaps 6 to 13V or so