[Boatanchors] URT-23 update

[eugene at hertzmail.com]

Hello all,
Seasons Greetings!

The last update I had indicated that the amp was putting out 500W on
35mw input from my rf generator, but that my exciter (T-827D) was not
putting out any RF and that I had begun the investigate. Thanks to
several of you, I switched my 5MHz oscillator to "INT/COMP" instead of
"EXT (NORMAL)."  But unfortunately, still no joy.

I spent the last 4 days working full time to figure out the problem.
First, I have to say how incredibly impressed with the navy manuals on
these units (The flexible blue plastic covered 4" thick manuals).  The
trouble shooting procedures are really excellent and easy to follow,
even for a novice like me. Kudos really to those who write these
manuals. I've never had any previous experience with military manuals,
but this is really top notch.

Unfortunately, the manuals I have are not quite right for the actual
versions of the components of my system. So in 90% of the cases, the
manuals are exact. But in about 10% of the time, the manuals are not
quite right. 

Using the manuals, I began to follow the procedures and discovered that
the band selector assy (not the switch, but a module) was not getting
the expected control voltages.  This further led to K3 which is a PTT
relay.  I was able to determine that K3 was not energizing when PTT.
But why? This then took my two full days to figure out what the problem
could possibly be with the Key Interlock circuits (which prevent the
Keying of the system when various conditions are met).

The navy manuals I have indicate that the amp has 3 printed circuit
boards next to each other (A8, A9, A10). Whereas my amp has only 2 PCB's
(A5 and A6). The navy manuals also indicate a 4th PCB called the ARC
protector assembly, also which my rig does not have.  It seems this is
an area that underwent some major changes during this rig's production
life.

I was able to figure out that the K3 relay in the exciter is actuated
from a 28V power source in my amp on board A5 (A5Q8).  This power source
could be switched off if an interlock condition exists (it is the output
of a switching pnp Q8). I found the base of transistor was behaving
properly under interlock and no-interlock conditions, but the output
(collector) of the transistor was not outputting the expected 28V when
it was saturated.  At this point I was suspecting a faulty Q8.

To test my theory, I disconnected the collector of Q8 from returning to
the card edge connector and the rest of the rig.  Instead I substituted
my own 28V voltage source.  SURE ENOUGH! This allowed me to energize K3
and lo and behold! I now have the exciter outputting RF! With the
exciter as the RF source, the amp is now outputting 1KW on CW, about
300W on AM at idle.  

So I have ordered a few 2N2905A's and will perform the replacement. I do
wonder, however, what could have caused it to go bad? And should I
expect it to go bad again if the true root cause of its failure has not
been addressed? Who knows! I guess I'll just have to wait and see.

There is still MUCH, MUCH work to be done. I plan to look at the output
of the exciter in my spectrum analyzer to check its purity and carrier
suppression.  Then I will try to do some checks on the amp for IMD etc.
But that will be off a while. I also want to play around with the built
in FSK module in the exciter which can connect directly to my 60ma
current loop and then interface with my teletype 28ASR and KSR loops.  

Lastly, once I know this radio can be put back on the air, I will have
to attempt to replace the fan with something MUCH quieter. Otherwise
keeping a microphone in the same house as this thing will be a challenge
(Literally, the xyl keeps thinking I'm vacuuming in my shack, ha!)  Then
there will be the project of getting the RF-601A remote antenna coupler
integrated and installed, maybe this spring (and oh, did I mention
trying to get a vertical installed). It never ends!

Thanks again to everyone who has helped with ideas along the way.  This
has been the singularly most challenging troubleshooting project I've
encountered (the problem of K3 is just one of several problems I've run
across!). 

Happy Holidays, 
73 Eugene W2HX