[TenTec] Corsair II keyer problem

[James C. Owen, III]

--- peter barville <peter@barville.freeserve.co.uk> wrote:
> 
> 

> When the keyer decides to send uncontrollable dashes, pin 19 is
> sitting
> at almost zero volts (instead of the 5 volts which should be
> present
> without the dash contact of the paddle being made). 

If Pin 19 is at zero volts when it should be 5V then there are
only two possibilities. 1) the pull-up resistor R14 is bad or the
5V to the hot side of R14 is going away. 2)there is an internal
failure in the chip U10 that takes that pin to ground.
I'm betting on a bad R14 or maybe a bad solder joint.



> I am surprised that any chip fault is a) intermittent,
> and b)
> manifesting itself in two different ways.  Why does the rig
> never power-
> up with the keyer fault present?

Chips can and are intermittent. This assumes that the failure is
not a complete junction failure. There are quite a few wire
bonding failures that crop up from time to time. Thermal cycles
cause stress on the wire bonds and if not enough slack was left
can cause a bond to break.
I think that the reason it may not show up at power-up is due to
temperature. When cold good contact is made-hot, bad.
If you replace the chip and find it really bad and you want to
know what was the cause of failure; if you will pop (easier said
than done) off the case top I will be glad to to inspect it under
my Zeiss microscope and take pictures of said failure, if found.
Oh! you're in "G" land, guess shipping it not a good idea.

                        73
                      Jim K4CGY

> 
> Does this sound like a chip fault to you?


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