[Yaesu] FT-101EE Modulation Problem

[Walter A. Hutchens]

Thomas asked:
> What's been happening is that I'm getting an approximate 100 watts out at
> 280 mils in the CW/TUNE position but only approximately 30 watts out at
> 100 mils on USB phone. Also when I modulate in USB the ALC swings way left
> out of range, even with the mic gain cranked way back to 2 or less. This
> excessive swing ALC happens whether the RF processor is on or off.

Evidently those in the know have been doing as I have and not reading the 
list closely as we struggle with whether Yaesu service does or does not, um 
... technical term ... suck.   So you have the second team taking a stab at this.

This sounds like instability -- something is oscillating but considerably off 
frequency.   The large ALC response with low gain setting says that the ALC 
detector (grid of PA, right?) sees it but your wattmeter does not; first thing 
I'd check is PA neutralization, though I'd expect problems there to show on 
the wattmeter.  

If not neutralization then the bogus signal is getting through the driver 
stage.   However if the problem occurs *only* in USB then some 
considerably earlier stage must also be in the game or may be solely at fault 
so I'm wondering if it's also on LSB.     

Since the problem is only on the new bands, the final mixer stage is the 
earliest likely participant.   

If you have access to a spectrum analyzer it will point you in the right 
direction rather quickly -- a heck of a spur is reaching the PA grid and its 
frequency should announce the stage in which it was generated.   If no s.a., 
I'd reexamine the installation of the WARC mod first, looking for 
component location, lead dress and bypassing problems, then checking any 
special alignment requirements.   Yaesu didn't plan for this conversion 
scheme so there's the possiblity of more critical adjustment to avoid an 
undesired mixing product that could lead to instability.   For example they 
may say something like "Adjust Lxx for exactly 0.2 v RMS at test point" and 
if so, 'tune for max' could cause problems.

If the WARC mod is okay, recheck the processor.   I did the processor 
install on a -101FX; the only thing I found tricky was that due to its location 
that board is subject to pressure on the filter if the set is placed upside 
down with the covers off and I had to troubleshoot some connection or 
broken trace problems.   The details have been lost in the internal ear-to-
ear winds ...

Walt Hutchens
KJ4KV