W4RT's OBF817 CW narrow doesn't work properly in New 817ND

To refer FAQ of W4RT's site,
"Does the One-Board Filter work the same in both the FT-817 and the FT-817ND? Yes."
But in my case, it was No.
Although W4RT Electronics says
"The OBF has been installed many times in both the 817 and 817ND without any problem." ,
here's a story 'bout my trouble fix of installing OBF to 817ND below.

Yamada Radio Clinic

W4RT's site has been updated in September 2006.
Now,their FAQ has been changed like this.

I have the FT-817ND. Does the OBF install the same as in the FT-817?
Maybe, but some of the FT-817ND units have two very-small SMT resistors placed in the filter circuit where SMT capacitors were used before. If your FT-817ND has the resistors, they need to be preplaced with the proper capacitors. This requires proper SMT skill and equipment. If you don't have both, then we strongly urge you to have W4RT Electronics perform the installation for you. Please see the manual.

That's nothing but what I pointed out below first time in November 2005.

The other day, a good ol' friend of mine Steve sent me a e-mail.

" Hi, I'm going to purchase W4RT's One-Board Filter for my new FT-817ND. Can you install that ? "

I read the Installation Manual and it seemed to be very easy for me.
So I told him, " Yeah, I think I can. Go ahead. "

Steve has two sets of FT-817. He sent me both of them.
The old one has stock Murata SSB Filter and Yaesu genuine optional Collins CW filter.
And I installed OBF to the new one carefully.

After I installed OBF, I compared performances between these sets.
Then I realized that there were multiple beats when I received CW-narrow with OBF.

I thought that something was going wrong in OBF.

# It may be hard to realize this symptom because it has nulls certainly aside the peak.
# But other peaks exist over the null.
# Please try to listen to a single carrier and turn your tuning knob.

Steve sent a e-mail about this difficulty to seller, but they didn't understand the fault on this OBF.
May be they are doubtful about my skill.

Well, I've been a ham radio and a hand crafter for more than 35 years.
It seems to me that the faster way is resolving by myself rather than spending time for boring negotiation.
I'll test this OBF. I'll fix this symptom.

This is the multi beat symptom. I connected SSG(Megro/MSG-2610) to the antenna terminal and read AF output by Volt Meter. Receiving frequency was fixed at 10MHz and I swept SSG frequency around 10MHz. The blue line is OBF and the pink line is stock Murata SSB + Yaesu genuine Collins CW filter. I thought that SSB filter was alive even when receiving CW-narrow with OBF.

If both of the wider filter and the narrower filter are active simultaneously in paralel, you may think that the wider will be dominant. (concerning only with the amplitude factor) But it's more complicated matter. The mixtured overall performance will be turbulenced with nulls, because the narrower one has a great deal of time-delay/phase changes near at shoulders of it's corner frequencies like ==>> this (by Rockwell Collins) I guess that's the reason of the symptom in my case.

old FT-817 IF The SSB filter is coupled by capacitors.

new FT-817ND IF It had changed to be resistor coupled in new 817ND.

problem between OBF's SSB-fil and new 817ND The OBF filter has "T" shaped resistor network in its input. It makes current flow like this, and makes Diode switches always ON. The SSB fiter is alive even when receiving CW-narrow.

Fix Step 1 Change jumper wires (from OBF to 817ND main board) into 0.01 micro farad capacitors.

Fix Step 2 Short cut the R1498 and R1499 on 817ND main board. Gotta be critical work !! Maybe you can leave them.

Then I plotted the filter response again. Now, it's working properly.