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RCI6900F150 problem with bias and modulation

sp5it

Master of puppets
Jul 9, 2009
2,760
3,708
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Poland
www.qrz.com
Hi.
Customer brought today RCI 6900F150 to tune.
I connected dummy load, pramplified mic and noticed no diffrence between stock and new one.
No response for AM mod pot VR17, limiter in place.
So I removed limiter - no diffrence. Strange.
I disconnected PA module, power went down (no suprise) modulation stays on the same level.
I connected antenna and suprise: I had loud, screaming audio in AM, but PA module disconnected.
I connected back PA, power went up to 50W carrier, modulation goes down to previous level.

40 mA bias on driver, 32mA on final, pot is at the edge, no chance to go further with bias on final.

Someone have an idea why is that and how to fix it? I never saw that before.
BTW PA is built with SD1446, SM says that it should have 2290 in place. Is that normal?
Mike
 

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