[Premium-Rx] R&S EK07 Blows Fuses even when switched off!

[Charles Steinmetz]

Warren wrote:

>Anyone know what is in between the line cord and the on/off power 
>switch in the EK07?
>My EK07 now blows fuses as soon as I plug it in, even if the power 
>switch is off!

Do you have a schematic?  It is easy enough to follow, even if you 
don't speak German:

Power comes in and is routed in the wiring harness 
("Gesamtverdrahtung") to a fuse and line filter assembly (presumably, 
this much is OK or you would be blowing your house fuse or the outlet 
fuse, if there is one).

Power enters the fuse and filter assembly at terminals 1 and 2, and 
exits at terminals 3 and 4 to the wiring harness, then goes to the 
front panel ("Frontplatte") via Bu6/St6, contacts 2a and 2b.  There 
are three fuses in the fuse/filter assembly.  Si2 and Si3 are 1A 
fuses (presumably, 2A at 120v) on the two legs of the power 
input.  Si1 is a 400mA fuse on the 220v DC supply (which is switched 
at the front panel in cam switch S4).

At the front panel, both sides are switched in S4 and exit the front 
panel to the wiring harness on St6/Bu6, contacts 1b and 1c.  From 
there, the wiring harness feeds the power supply ("Netzteil") through 
Bu5/St5, contacts 6a and 6c (St5 contacts 6a and 6c are connected to 
the power transformer primary winding).

The side of the line that goes to St5, contact 6a on the power supply 
also goes through the harness to St7, contact 5a, where it pairs with 
a wire from a 150v winding on the transformer primary that feeds a 
constant 150v (regardless of incoming line voltage) via St6/Bu6, 
contact 6b, through the wiring harness to St7, contact 5b.

If the radio does not blow the house fuse (or the outlet fuse, if 
there is one), but blows the internal fuse(s) when it is plugged in 
even if the power switch is off, then you have a problem between 
terminals 3 and 4 of the fuse/line filter assembly and the power 
switch, S4, on the front panel.  That doesn't leave much -- only the 
line filter itself, the wiring harness, and the switch wiring on the 
front panel.  (Of course, if both AC line sections of S4 are shorted, 
the problem could be downstream of S4.  But simultaneous shorts in 
two switch sections are unlikely.)

Best regards,

Charles