Hi, I am cross posting this from my blog. The blog is here:
http://cupcakecarnival.net/2013/03/07/ten-tec-t-kit-1260-6-meter-fm-transceiver-final-dying
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/tentec_kenwood.jpg.html
In the picture above, ignore the Kenwood TM-261A 2 meter radio on top
of the Ten-Tec. I got T-Kit as a Christmas gift in 1998 just after
getting my license in October of the same year. I had a ton of fun
with it the following summer on sporadic E band openings and I have
QSL cards from up in the north eastern and eastern parts of the US to
prove it. At some point though it stopped transmitting. Last I checked
I could hear it fine on my Dad's handheld Icom IC-T81, but only
really, really close by, like within half a block. Hooking it up to a
MFJ-864 SWR Wattmeter shows *no* movement in needles when
transmitting. I went through the manual and tested all the voltages at
the test points and they were mostly within the expected ranges. So I
called Gary at Ten Tec T-kit tech support and he said he was 99% sure
it was the final and suggested replacing it. Unfortunately the
original 2SC1971 is no longer available. The replacement for that is
the NTE 342:
http://www.mouser.com/Search/ProductDetail.aspx?R=NTE342virtualkey52600000virtualkey526-NTE342
I got this and replaced it and tried it out and what I observed was
that the needle on the MFJ-865 SWR Wattmeter moved once and then went
down immediately. The T-Kit went back to operating the same way it had
before I replaced the final.
Originally this kit came with a Supplement and a Tech Bulletin to the
Supplment. In the Tech Bulletin it provided an extra capacitor and a
resistor to create feedback "to reduce gain at lower frequencies,
therby stabilizing the amplifier." I had alway suspected something
might be wrong with this circuit that could cause the final to short.
First, here is the tech bulletin:
Tech-Bulletin-1260-498-1:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/Tech-Bulletin-1260-498-1.jpg.html
Now looking closer at the resistor in this circuit today I noticed it
looks brown in the middle, like it is shorted out! Here, take a look:
feedback circuit 1:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191305.jpg.html
or
feedback circuit 2:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191339.jpg.html
Am I on to something? Before I replaced the 2SC1971 with the NTE342 I
wanted to remove that circuit for fear it was at fault, but I didn't.
In addition to that you may have noticed in the tech bulletin from
above it added a DC blocking circuit on the SO-239. I thought maybe
something could have been wrong there, but I have no "smoking" gun
like the browned resistor from above, but here are some pics of that:
DC Block 1:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191347.jpg.html
DC Block 2:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191425.jpg.html
DC Block 3:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191434.jpg.html
Do you think I should be worried about that?
Especially after finding that browned resistor I'm tempted to remove
it completely or replace it and buy another NTE342 and try again! Any
advice appreciated.
For reference here are some of the relevant documents from the
instruction manual:
(as in the above links there is an arrow above and in the middle of
the reduced size image that shows the full size scan)
Schematic 1:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/Schematic.jpg.html
Schematic 2:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/Schematic2.jpg.html
Schematic 3:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/Schematic3.jpg.html
RF Section schematic and drawing:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/Phase7-1.jpg.html
Circuit Board X-Ray:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/CircuitBoard-X-Ray.jpg.html
Mechanical Assembly:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/Mechanical_assembly.jpg.html
Top of circuit board after NTE342:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191508.jpg.html
Close up of RF section showing NTE342:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/IMG_20130307_191522.jpg.html
Bottom of board after original construction:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/tentecbottom.jpg.html
Top of board after original construction:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/tentectop.jpg.html
Back of radio after original construction:
http://cupcakecarnival.net/gallery/main.php/v/Radio/Ten-Tec-_T-KIT-1260-6-meter-transceiver/tentecback.jpg.html
73,
John, KG4AKV
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|
