Sir Jimkarl . . . . .
IF the
WK-3700 is schematically being the same as the
WK-3000 here is a simplified and dedicated schematic, that is showing solely your power flow in both battery and external power connections.
In order not to have to use an internal / external power changeover switch they have used two power steering diodes for isolation and routing, to automatically let you revert between a use of a power pack or the internal batteries.
Consulting the referencing:
If you can turn the unit on and off with internal battery power . . .all is well up to my marked in
RED A and
BLACK B markers.
Now take DC voltage metering leads up to my marked in
RED A Prime ad
BLACK B Prime markers. If the voltage read out there is the same as the voltage read out back at
RED A and
BLACK B markers, all is being well up to that point.
You then just have to pull one cell, to drop battery power, and ohm out from the
RED A Prime marker to the end of the connecter . . . .note that the plug entry switch is non functional / by virtue of being continually shorted.
That will have tested the
POSITIVE power leg.
Ohm out between the cathode of D202 to the ground collar of J201.
That will have tested the
NEGATIVE power leg.
Plus, it's also confiming the integrity of the L202's set of inductive filters.
Final test would be to test the D201 and D202 steering / isolation diodes.
Do a swap probe leads in low ohms test on each one and if not being dead shorted, then do a like diode test mode in order to get / ascertain their forward voltage drop / loss in hundreds of millivolts.
Do note that they are using 1N5822 Schottky diodes, in order to have a low voltage drop / loss since they are being used on both legs.
Also they are 3A rated . . . a bit of overkill in this situation / application.
Now . . . .waiting to see if you either find a wiring discontinuity path or a shorted diode(s) .
Le TECHNICAL REFERENCING SCHEMATIQUE . . . . .
1N5822 Diode Data Sheet
http://pdf.datasheetcatalog.com/datasheet/fairchild/1N5822.pdf
73's de Edd