[Yaesu] FL-2100B, Help Troubleshoot...

Fri May 18 21:31:21 EDT 2012

Roger there is... Didn't think I would need to mention it since I mentioned 
the SWR. Dug out my old Heathkit HM102 and put it inline, SWR is about 
1.5:1 on 10m, a slight tweak of the coil and its flat now.
The problem was a bad solder joint on the tap at the tank coil, turns out 
when the amp was warmed up it got intermittent and it was driving me buggy 
finding it. As you could imagine, I would test it, nothing, let the amp 
cool and rest and walk away for a while and come back and start going 
through everything and it all looked good continuity wise through the input 
and bandswitches, etc. But warm it up and I would get a blip or two of 
output and then nothing again! Talk about a hair puller. Then I decided to 
get the chicken stick out, pull the plug and bleed everything off and check 
continuity quick while it was still warmed up after being on the net and low 
and behold its an open circuit on the output side! A little heat, solder, 
and its all better now.
73,
Scott KBØNLY
-----Original Message----- 
From: Bill Aycock
Sent: Friday, May 18, 2012 8:13 PM
To: KBØNLY
Subject: Re: [Yaesu] FL-2100B, Help Troubleshoot...
Scott--
I'm puzzled; you appear to be very knowledgeable, but I don't see any
reference to checking drive signal on 10. Is there any drive, at the right
frequency?
Bill--W4BSG
----- Original Message ----- 
From: "KBØNLY" <kb0nly at mchsi.com>
To: "Yaesu Reflector" <yaesu at mailman.qth.net>
Sent: Friday, May 18, 2012 11:39 AM
Subject: [Yaesu] FL-2100B, Help Troubleshoot...
> Hey all! I got a question here on the Amp I have been working on, I have 
> worked on a few of these but this one is acting odd.
>> Here is the story... The amp had a burned band switch, I helped Multi Tech 
> Industries design a new one, it will be on the market soon in case anyone 
> needs one, and I got the switch installed. New tubes.. A couple new 
> capacitors, the 1000pf cap on the plate end of the RF Choke was broken by 
> the previous owner removing the blown bandswitch. And one cap on the T/R 
> relay, a bypass cap, was broken as well, looks like someone just caught it 
> on the bench and cracked it while trying to work on the amp.
>> Tossed in a new set of tubes, let it warm up a bit, checked the bias, 
> adjusted. Tried 80m, perfecto... 600w output with 50w drive and the tubes 
> are looking good, voltages and current looking good, no problems. Drop to 
> 40m, same thing 600w and no problems. Drop to 20m, again no problem and 
> 600w output. Drop to 15m, about 400w output and a very hard to find dip 
> on the plate, but otherwise the current is where it should be and it looks 
> ok, I think on 15m I actually just have a bit of an input SWR problem and 
> the coil for that band has been adjusted its not in the stock location so 
> I will have to put the analyzer on it and tweak it.
>> Now comes the problem... 10m is dead. According to my radio the input 
> SWR is below 2:1 as its not backing off, the current on the amp comes up 
> but the plate capacitor has no apparent dip, meter never moves, tuning 
> capacitor doesn’t seem to make any difference either, there is ZERO output 
> on 10m. I mean dead dead dead. So the only thing I can think, since the 
> output bandswitch is brand new is that I have a problem in the input 
> section of the amp. I checked the input bandswitch for continuity in the 
> 10m position and its fine, I inspected it with a flashlight and a small 
> dental mirror, no contact problems there. The coil for 10m looks ok, and 
> the tuning slug doesn’t appear to have been moved.
>> So, could the cap on the 10m input, 1000pf, be bad causing this? If so 
> why wouldn’t my radio be complaining about a high input SWR? And why 
> would the plate current come up when drive is applied but no output? Very 
> very odd....
>> 73,
>> Scott KBØNLY
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