Restoration of the Tempo 2020 transceiver
(New material added 12/16/2009)
The Tempo 2020 HF transceiver is quite a rig. Until I hooked up with Erwin, KI4TBD, I'd never heard of it, at least I don't recall it. Maybe it was popular during a period where I wasn't much involved in ham radio stuff; i.e., during my tour of duty in the Navy, and establishing a career in the nuclear energy field thereafter.
The 2020 has quite a following among boatanchor aficiandos. Check out the Tempo_2020 group at www.groups.yahoo.com.
To check out the receiver's sensitivity and to calibrate the S-meter, I normally would have used my formerly-trusty URM-25D signal generator, but I haven't gotten it working after changing out all of the paper capacitors (very gooey mess, all of them...they are the ones that look like vintage postage-stamp micas.) So, I decided to use my K8IQY-designed homebrew -20 dBm test source, which is a fixed frequency 14.060 MHz device. However, that's not low enough to check the minimum discernable signal, even with my homebrew 80 dB step attenuator. So, I built a 40 dB fixed attenuator to go between the source and the step attenuator. The source and 40 dB attenuator combo checked out accurately at -60 dBm on the log power meter, by the way. Those three pieces of equipment are featured on this site, under "Completed Projects".
Calibration of the S-meter was just a bit of a hassle. I intended to use the international standards for S-meter calibration. First problem, the Tempo (Uniden, actually) procedure doesn't speak in terms of dBm. Rather, it uses uV from the sig gen, and also dBu later in the procedure. Fortunately, there are several online calculators to convert from uV at 50 ohms, dBv, dBu and dBm. Second, the three pots used to set the S-meter are interactive. It's very easy to peg the meter on a reasonably strong signal, and inexact adjustment of the meter at the low end can cut the received signal to the rest of the receiver chain. Lots of back and forth with the low, S9 and high end pots. Third issue, and I missed this fact until late in the process, Uniden designed this rig for 4 dB per S unit instead of the standard 6 dB per S unit. I ended up settling for a fair calibration between S6 and 10 dB over S9, obtaining between 4 and 6 dB per S unit. Oh yes, and I checked the situation using a replacement board from a parts unit with the same middling result. Inexact S-meter readings are common with modern rigs, so that's about all I could expect from one that's over 25 years old.
During my work on a couple of these rigs, I've documented some procedures for dealing with some common issues. Broken or cracked sprockets in the preselector and Bandswitch ladder-chain drive trains are very common due to aging. Sometimes the cracks are small enough that the sprockets may be repaired. For some, replacement is the only option. I've done both, and I've documented the process in detail with procedures and photos. Also, the shaft couplers may be broken. I've replaced one for the PA compartment shaft coupler (the most difficult one to replace). All components, knobs, sprockets, shaft couplers, etc. are on 6mm rather than 1/8" shafts. This can make finding replacement parts more difficult. The following PDF and zip files are available for download:
"Tempo 2020 Preselector Sprocket and Chain Replacement"
"Tempo 2020 Preselector Sprocket and Chain Replacement Image Files (zip)"
"Tempo 2020 Sprocket Repair"
"Shaft Coupler - PA"
You'll need a PDF reader such as Adobe Acrobat Reader, or even better, the much less hard drive space-consuming Foxit Reader, available from www.foxitsoftware.com...That's what I've used for several years.