Shorting Bar? - Motorola HK 45-2 Tuner

[jpatti75]

Hi gang,

What be the purpose of the shorting bar in this Motorola tuner diagram, and when is it necessary to move it to the Mono or Stereo position? Does it come into play when using a multiplex adapter for FM stereo?

Ignorantly yours,
JP

 

[cademan]

I want to say that you would remove it when plugging in an MPX adapter but I am not sure of the function without the schematic. If you have the above page of the service manual, you should also have the schematic.

 

[Tom Bavis]

I'd assume that's the socket for the multiplex adapter - jumper wire when there's no MPX. And I'd be wrong - just looked at the 45-3 schematic (too lazy to go downstairs and find the 45-2). In the STEREO position, it bypasses the FM de-emphasis network so that a MPX adapter can work. So you'd need to move the jumper and plug in a separate MPX adapter to have stereo. Most tuners provided a second jack for multiplex output - this one has only one.

 

[jpatti75]

Thanks, gents. Well, this probably explains why I got no signal at all when I plugged in an MPX adapter and set it to stereo. Here’s the schematic (hopefully legible when you click on it):