How to Align a Ten Tec Omni 6 Plus With Ease

Alignment Methodology

Aligning a radio is a lot like treating an illness. You should do as little as possible to achieve the desired result. If the system already meets the published specification, don’t mess with it. In other words,

First do no harm.

On the other hand, a repair that scatter-shots a variety of parts into the radio will likely need at least some alignment. That’s the situation here. In a recent repair of a Ten Tec Omni 6 Plus, I found numerous problems. What follows is the minimal alignment process I used to get the radio back within spec.

Besides wanting to molest the radio as little as possible, the Ten Tec Omni 6 plus documentation is minimal at best. And, there aren’t any professionals at Ten Tec to consult. We’re on our own. So consider each adjustment carefully and understand what it does before proceeding. Is it really necessary?

Further, there are many more adjustments available in the Omni 6 Plus than are mentioned in either the Operator’s Manual or this blog post. Resist the urge to play with them. Unless there’s been a serious insult to the radio, they’re unlikely to have changed much in the 20 or so years since the radio was new. Also, more sophisticated gear and techniques than most Amateurs have access to are required to adjust them successfully.

You Have Been Warned

Ten Tec Omni 6 plus: Module by Module

Here is the alignment process, roughly in the order I pursued. As you read through each section, be sure to click on the accompanying photos, since many of them show details that are not visible in the thumbnails.

Set Master Clock (Logic Board, 81606)

As mentioned in the previous post, the Master Clock is the place to start. Connect an accurate frequency counter to pin 9 of U12 on the Logic Board and adjust C31 for exactly 10 MHz. Patience and a steady hand are your friends here. Be sure to use a non-metallic alignment tool. After adjustment, the clock seemed stable as I looked at it on the counter. But as we’ll see, we weren’t done with it yet. More later.

Another post in this series describes one approach to a very accurate and stable frequency reference. You might find it helpful.

9 MHz Crystal Filter Board (81782) (Rcvr Tuned Circuits)

The alignment for the Receiver Tuned Circuits on this board is described clearly in the Omni 6 plus manual. There are four tuned circuits in the receive path to peak. I used the Elecraft XG3 for the signal generator and a Digital Volt Meter (DVM) for this adjustment.

IF/AF Board (81602) (IF)

There are two tuned circuits (L3 and L5) to peak on this board. An off-air signal or the XG3 signal generator mentioned early can be used.

Pass Band Tuning Board (81781)

A Voltage Controlled Oscillator (VCO) on this board is used to adjust the receiver Pass Band Tuning (PBT). The “test point adjacent to the coax jumper cable” didn’t exist in this radio, so I simply connected a test lead to the center conductor of the coax next to L17.

Pay careful attention to the PBT knob on the front panel of the radio as you adjust C24 and R18. I missed this detail at first and wasted some time trying to understand why the alignment didn’t seem to work. Once I reread the instructions, the alignment worked perfectly.

TX Audio Board (81597) (BFO)

I spent a lot of time on these adjustments. As mentioned in the previous post, the instructions have errors and the tiny trimmer caps are jicky. Be patient and don’t drink too much coffee before trying to set these caps.

The corrected trimmer order is as follows:

• CW transmit or Tune, adjust C16 for 9.000400 MHz
• LSB receive, adjust C10 for 9.000000 MHz
• USB receive, adjust C12 for 9.003000 MHz
• FSK Space, adjust C13 for 9.002295 MHz
• FSK Space adjust C18 for 9.002125 MHz

You might find reading the section on this alignment process in the previous post helpful.

Xtal Osc. – L.O. Mixer Board (81595) (VFO/LO)

Not much is said in the Ten Tec manual about aligning this board. After a considerable amount of noodling around the ‘web, I found this posting: “Ten-Tec Omni VI Plus Model 564 Frequency Adjustments.” I wouldn’t try making any adjustments on this board without reading the document. Be patient, it loads slowly from an overseas archive. I’ve also linked a PDF version of it below. If you know who originally created the document, I would love to know it. Please post it to the comments below.

IF/AF Board (81602) (S-Meter)

The S-meter alignment should be done after all other receiver adjustments have been made. You’ll also need a calibrated signal generator. Again, I used the Elecraft XG3 to obtain the 50 uV signal (-73 dBm, equal to S9 on the S-meter) and ran it through a switchable attenuator to obtain the S3 calibration (-103 dBm).

This adjustment is challenging, even after correcting what I think were wiring errors in this particular transceiver. Getting the radio to accurately indicate S9 is easy, but S3 not so much. I ended up settling for plus or minus 1 S-unit. But then again, have you ever encountered a receiver from this era or earlier that accurately indicated signal strength?

9 MHz Crystal Filter Board (81782) (Final amp Pwr, Ic, SWR Mtr, ALC)

You’ll need a 50-ohm dummy load, an accurate RF watt meter and a DC Ammeter for the transmitter alignment. I used a clamp-on DC ammeter that covered the 20-30 amp range, and that worked fine.

The manual’s description is a little sparse, but the goal is to adjust R46 (ALC) for 100 Watts, R52 (FWD Power) for 100 Watts deflection on the radio’s multimeter, Calibrate R57 (Ic) to correctly show input current to the radio, and set current limiting with R54 (Ic Set). This prevents the radio from drawing too much current with antenna mismatches.

The adjustments are not difficult and the instructions in the manual are accurate.

Power Amplifier (81611)

There are only two adjustments in the PA module — PA bias, R19 and R15. The process is clearly described in the Ten Tec manual. On this particular radio, I found that one of the pots was all the way at one end of its travel. The radio still made full power though, so I accepted it.

This completes the alignment. The Ten Tec Omni 6 plus now met specs in sensitivity and power out as expected.

Testing – Master Osc. still unstable

After completing the alignment, I thought it was ready for FT8 use. After hooking it up in the shack though, I could see that the frequency instability was still there. Checking with my GPS disciplined (GPSDO) frequency counter, I could now see that instability clearly. The damaged TCXO was borked, and I didn’t have a spare logic board to canabalize.

Well, the GPSDO project also suggested a fix, although a little more work than I would have preferred. We’ll talk about that in the next post.