After the very first production run of the keyer, the parts driving the PTT
outputs
(and CW outputs for that matter) were replaced. Both were photo-darlingtons,
but the newer part was empirically shown to pull enough current for the
Yaesu rigs while the original part was not. I have forgotten the exact
serial
number where the parts were switched over, but it was something in the 130
to
150 range. (This all happened several years ago).
After opening the box, its easy to spot the ones with the old parts because
the original configuration was 4 by 4-pin DIP packages, part number
H11A817CQT, Each one drove one CW output or one PTT output.
The new configuration is 2 by 8 pin DP pages.
The new part, (the 8 pin one) is available from digikey: PS2501-2.
It fits in the same circuit board holes as the old one.
Wayne
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