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This site has a pretty good discussion about your issue with the TC-2.
In essence, CR-1 (not ID'ed above) can be replaced with a 1N4007 without any issues, except that the 1.2k resistor (shown as "1200Ω" in the schematic) may have to be adjusted so the meter can be accurately zeroed.
Have you tried putting the new (or old, for that matter) diode into the circuit in reverse of the schematic (as Nigel offered in post#4)? That action certainly won't hurt the diode.
The site I referenced had a post stating that HK screwed this one up (hard as that may be to believe ). Even suggested that the Knight(Kit) 600 schematic had it right... (and you'll note that it is, indeed, reversed from the HK schematic).