[Yaesu] Re: FT-1000D - slight lightening damage to (modified) LPF unit - the solution

[Chris Codella, W2PA]

Just thought I'd follow up on the resolution to this problem in case 
anyone else runs into this.  Thanks to the group for the various 
suggestions and observations.

The lightening strike was not direct and took out a couple of other 
random pieces of electronics in the house, including a circuit board in 
the second floor air handler for the heat and A/C, the DSL modem and the 
wireless router.  When I turned on the FT-1000D no signals could be 
heard in the main receiver so I knew something got zapped (the 
sub-receiver was unaffected, as was the transmitter).  But as I was 
tuning across 40m that night, I heard very weak carriers from 
broadcasters so I knew most of the rig was fine and the damage was 
likely very close to the antenna connection and I was hearing strong 
signals bleeding through very slightly.

That tuned out to be true, and all the damage was confined to the LPF 
unit, on which two capacitors, two transistors, and a diode, got fried.  
All of the components were associated with the receiver/transmitter 
antenna switching circuit.  There are at least two versions of this 
circuit, the original one having an NPN self-biased compound transistor 
(BA1A4M) controlling the ground side of the relay coil, and the later 
one that uses a PNP version (BN1A4M) controlling the 13V side; in both 
cases it's designated Q7203 in the schematic.  My FT-1000D looks like it 
has the LPF board for the original circuit but had been modified by 
Yaesu per the service manual to become the later version.

Anyway, that relay driver transistor, Q7203, got zapped along with 
Q7202, an NPN that's half of a complementary pair of transistors that 
biases the main switching diode either to isolate the transmitter when 
on receive or connect it to the output when transmitting.  The pair also 
drives Q7203 to control the relay that isolates or connects the main 
receiver antenna.  In addition, C7288 got fried, an SMD capacitor in the 
transmit line that isolates the DC in the switching diode from the 
antenna output.  And C7278 a bypass capacitor on the collector of Q7202 
(the one that died) met its end as well. 

It's difficult to find some of the original parts Yaesu used, but there 
are readily available substitutions.  Here's a summary of replacement 
parts I used that all work fine.

Q7202 - the 2SD667 can be replaced with an NTE289
Q7201 - the complementary PNP, a 2SA684, can be replaced with an NTE290 
(this wasn't necessary in my case)
Q7203 - these self-biased PNPs seem to be available here and there.  But 
I used a Fairchild GC557B which is the equivalent to the the stand-alone 
transistor used in the module (a 2SA1175), combined with two small 10k 
resistors, one in the base lead, one base to emitter.
C7278 - 0.1uF disc that ought to be in most junk boxes, or at Radio Shack
C7288 - This one was a bit tricky.  I first replaced it with a 200V, 
0.1uF SMD capacitor (Kemet C1812 type).  Although it has the same rating 
and value as the other one in the transmit line, and matched the specs 
in the schematic, it was quite a bit smaller in size than the one I took 
out.  When I fired up the rig, it self-destructed as I applied full 
power on transmit.  I speculate that it was mismatched with its mate, 
C7287, on the other side of the switching diode and took an over 
voltage.  So I replaced both capacitors with a the 1000V rated Murata 
2220 (GRM55DR...), which by the way is just about the same size as the 
200V one I took out, and everybody's happy now.

All the parts were available from Mouser.

73,
Chris, W2PA