Often, I get emails from hams who have seen my videos or found the blog and will ask questions regarding radios/rigs I have worked on. One showed up yesterday from a ham in one of the Scandinavian countries. It involved a Ten Tec Model 544. I have some videos on You Tube covering several Ten Tec Radios and that is, I guess, how he found me. Here is summary of one of the problems.
The radio receives on 8oM but does not transmit on 80M and when in transmit there is no indication of power output either at the antenna or on the meter. But if you open up the power level it trips the circuit breaker.
I should mention that Ten Tec Triton series radios are some of my favorite radios to operate and to repair. The reason is simple as the radios are built by using plug in modules and the service manual likewise is set up on a module basis. Pins on the modules actually let you look at key test points.
The Triton radios are intended to operate with a circuit breaker in line (or built in) with the power supply so when he said the breaker trips -- the radio was seeing 20 Amps of current with no output.
So how to respond to the inquiry and the answer is to start 1st by looking at the facts or information not provided. The email was clear that the receive section worked and that it was a problem limited to 80M. Thus you surmise the radios works on other bands.
Yes you have to be a detective to sort through the noise to find "whodunnit".
From the information supplied I went to one module schematic that was very familiar to me and that is the SWR ALC Board. In passing I spent a lot of time with this board in trying to fix a Triton II -- I will explain in a bit.
Not much to this circuitry but it provides several critical pieces of information. At the very bottom of the schematic is a reed relay that has its normally closed contact in line with the antenna to the receiving circuits. When the rig is placed in transmit that receive antenna line is shorted to ground thus protecting the Rx section from RF. Critical fact#1: It can Receive on 80M while the transmitter section has an issue!
In an earlier version of this circuit there was a pair of back-to-back diodes on that line connected at the point where you see Rx Ant. I bought a Triton IV that supposedly was struck by lightning while being off but connected to an antenna. I got it really very really cheap as it was listed as being blown! Yep, those two diodes were fused like a short. The total repair cost was 4 cents and the radio worked perfectly after replacing the diodes. I got lucky!
Look now at the upper left-hand side and you will see where the RF from the power amp stage passes through a small sampling transformer that provides a sample of the RF output to generate the ALC voltage. If there is no output from the Low Pass Filter, you will see no ALC and if cranked wide open the breaker will trip as you are feeding an open circuit!
Now look along the right-hand side a look for the terminal marked ALC Lite. The Triton series early vintage had a small incandescent 6.3 VDC grain of wheat bulb that would flicker on voice peaks which was intended to show only a flicker for proper operation. Just looking at that nomenclature you would think a Voltage was being supplied to that bulb. Well after a week of chasing my tail I realized that the bulb was not being supplied a voltage but in fact was supplying the voltage for the Darlington pair.
Well in the master schematic off in a corner it showed that small bulb being connected to 12VDC and then to the terminal marked ALC lite. The bulb filament was blown and thus no juice to the Darlington circuit! Later versions had an LED which was more durable.
So, my conclusion was there was no RF being supplied to this circuit on 80M but that indeed RF was being generated thus the Circuit Breaker tripping. Often on 80M operating with a high SWR will burn the switch contacts on the switch wafer.
I suggested another test before looking at the 80M wafer. That was to pull the RCA plug that feeds the RF Amplifier brick and to terminate that connection with a 50 Ohm dummy load. The next step was put a scope across the load. If he sees normal output and secondly you know the RF Brick works because you get output on other bands -- you are left with the switch wafer or the Low Pass Filter as the culprits. On the LPF it could be the same high SWR caused a shorted capacitor in the LPF.
I then said I would look at the switch wafer 1st as obviously you cycled it several times and if the contacts were dirty, they would have cleaned up and you should have seen some output. Mind you all this was done from 5000 miles away.
Well, I get an email back. Problem solved --he cycled the band switch, and the power output is now at full strength.
Then the off-frequency issue the second problem. I said that on 20M the PTO and Carrier Oscillator are used directly for the frequency generation. Thus, align that for 20M and then since this now is a 50-year-old radio the heterodyne crystals have drifted for the other bands and so align each of those to get the frequency correct on all bands.
After receiving the email back, I was sorry that I wasted so much of my time helping this guy -- time is critical to me. The other sad part is that I know how to do it --- and likely all he did was jiggle the band switch and did not look at the fault tree analysis on how to fix the radio by understanding how it works. My time was sapped and likely he got a free repair without understanding the how to fix it!
The next time I may just chose not to try help a fellow ham. I felt a bit used just because I know stuff. I thought of Mary Jo and all it took was a Bob's Big Boy hamburger...
73's
Pete N6QW