RCI-2980 boxcars

[TM86]

Have a RCI-2980 that I was running through an alignment on and got to AM modulation. Boxcars all day long and VR14 doesn't do anything.

I did find R249 clipped and replaced it. R245, R246, R247, and R248 appear to be intact. Checked the resistance of VR14, it does change relative to where the wiper is in relation to the fixed legs.

Tested TR53 and D92 with a TC-1 tester, both show good. Measured voltages on TR53 during AM XMIT are E=2V, B=0.99V, C=7.82V. There are no cut traces or bad solder joints that I can find.

FWIW, SSB ALC adjusts fine, no issues.

So now I'm stumped. The AMC is inoperable and I'm not sure where to look next. I'm considering swapping out TR53 but I don't think it will help much.

Any suggestions?

 

[Handy Andy]

Do I have this right?



Are you working in this area?

Does VR12 affect AMC in AM mode?

Why? It may not be related to AMC Not working - it may be from ALC Not turning off. AMC doesn't send much to work with even though it's screaming...

 

[TM86]

ALC (VR12) did have an effect. Which got me thinking about other adjustments that may also feed into this one. Found that AM carrier was a little bit too high to leave any headroom for modulation. Turned that down just a hair and had a beautiful envelope, just like the books show. My fault for not checking that after replacing R249.

Amazing what a good night's sleep and some good advice can do.

So now I've redone the AM power, ALC, and AMC portion of the alignment and everything looks good.

Hey, kids! Pay attention <tap tap> when Andy's talking to you.