[TenTec] Corsair II display problem encountered and repaired

[Jerry Volpe]

Display problem encountered and fixed.

Two weeks ago during the CQ WW DX contest I suddenly lost my display on 
the Corsair II. The internal keyer also ceased functioning as well (the 
keyer and display are controlled by the same processor). Turning the 
Corsair off and then on again resulted in a blank display (except for 
the decimal point). In all other ways the Corsair II worked correctly. 
Turning the Corsair II off for 20 minutes or more brought the display 
back to life... for a while. I did notice that it took  up to 10 seconds 
or more from the time the Corsair II was turned on till the display 
initialized itself. Before its initial malfunction the display always 
initialized with a second or less.

Ad investigation of the display circuit pointed to three suspects... U10 
the display processor, the 4.05 MHz crystal, and C6 a small electrolytic 
capacitor that provides a reset pulse on power on. As the frequency 
display was stable and accurate until the freeze I didn't think the 
crystal was an issue. The processor was still a suspect but it made 
sense to check the capacitor first. I removed C6 (connected to pin 28 of 
U10) and upon testing it I obtained very erratic capacitive readings. I 
replaced C6 with a known good 2.2uf/50 vdc electrolytic.

The Corsair II's display now initializes correctly and shows the 
operating frequency in about one half a second from power on. Since this 
repair there have been no further display lock up incidents.

Perhaps this may be of value to other Corsair II owners. If your display 
is initializing more than a few seconds after power on this capacitor is 
probably changing values and that is a good precursor to the problem I 
just experienced.

73,

Jerry, KG6TT
Fairfield, CA

-- 
Ralph Jerald "Jerry" Volpe
Amateur Radio Operator KG6TT
ARRL Member & VE
FISTS 12304

788 Chestnut Drive
Fairfield, CA 94533

kg6tt at arrl.net

510 325-7724
707 399-8838 FAX