Fisher 400 problem

merrylander

AK Member
This one arrived recently and everything is working except for the tuning eye. The tube tests good but all I get out of the limiter coil is about 0.85 volts and it does not vary much as you move across the dial. I had to pull the discriminator because the top ferrite slug was stuck, fixed that but still can't get the eye to move. Any thoughts?
 
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The tuning eye indicates the level of 19K in the MPX section, my schematic shows point D as the feed to the eye, D is pin 6 on the MPX, has no ties to the discriminator.
 
Hmm, missed that switch route, maybe dirty contact, Thanks Terry, why the diode inside the limiter? Got a CR-2040 on the bench at the moment soo the 400 will wait for another day.
 
Ratio detector diodes are in the can, was a gimmick to cut the amount of components under the chassis and get matched diodes.
 
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