Ten-Tec Jupiter Line Input Mod: I’ll skip this one, thanks

I love my Ten-Tec Jupiter. Very good rig! But I noted earlier that I had trouble feeding it audio for HF digital work because the line input via the AUX1 connector is remarkably sensitive. I had to put a 10:1 voltage divider in the SignaLink USB to cut the audio down to what the Jupiter would accept. It works, but the Jupiter is still too sensitive and the adjustment takes some finesse.

As it turns out, the later (black) Jupiters had a “small” modification so they wouldn’t be so sensitive. Thanks to reader Sal for pointing this out. Here’s the deal. Ten-Tec now offers a sound card interface similar in concept to the SignaLink USB, although without the knobs and adjustments. It’s called the “MODEL 712 – USB SOUNDCARD DIGITAL MODE ADAPTER CABLE.” But…there’s a warning that comes with the 712:

“NOTE ON USE WITH JUPITER HF TRANSCEIVER
“The earlier version of the Jupiter with the gray case and green screen is not usable with the 712 as a plug-and-play device. The later black case/blue screen Jupiter can be used as-is with 712. There is too much gain internal to the transceiver on the line input which makes use of the 712 problematic with the earlier Jupiter. There is a small hardware modification to the earlier Jupiter which will allow use of the 712 as a plug-and-play device; contact TenTec Service at (865) 428-0364 or service@tentec.com for information.”

I contacted Ten-Tec to inquire as to the “small hardware modification.” Garry Green, N4CJX, at Ten-Tec replied with a single JPEG image. I zero in on the relevant part in the following photo.

 
I wouldn’t exactly call this single photo a complete set of instructions for making the modification, so I investigated further prior to opening up my Jupiter. I dug into the instruction manual, which comes with extensive parts-layout drawings, schematics, and bills of materials. Here’s a close-up of Figure 4-15 from the original instruction manual, which is the parts layout diagram for the Digital Signal Processing (DSP) printed circuit board (PCB). Note that this is a high-res scan.  
 
As it turns out, the part is R52 on the DSP PCB. Okay, let’s find out what R52 is. Here’s a closeup from Figure 4-11, the audio input/output portion of the DSP PCB.
 
All right, we’re swapping out a 330K-ohm resistor with one that’s 33K-ohm, a factor of ten between the two. Fair enough. But, actual inspection of the circuit board reveals this:

Uh…yes, it’s a “small modification.” Very small. I put a dime in the photo so you can see just how small it is. Compare the size of R52 (orange arrow) with the “N” in “One Dime.” Also note that the integrated circuit just to the right of the part is actually a surface-mount device, itself very small.

So, I’d say the modification is “too small.” I’d need a microscope to fix this! Frankly, I don’t think John Q. Ham can attempt this without some seriously uncommon equipment. I certainly can’t! So…I guess my gray-box Jupiter will stay unmodified, and I’ll live with the quite-sufficient work-around I made to the SignaLink USB. It was a lovely journey into the depths of my Jupiter, but it has all the attributes of “look but don’t touch!”

P.S. Opening the Jupiter requires dealing with some screws with a weird star pattern that won’t accept a traditional screwdriver. I didn’t have the right tool, but found that a 5/64-th hex key (Allen) wrench, if used gently, works.