KPA100 Voltage checks

[Rick-94]

Hello all, I am to the point of the first voltage tests on my KPA100 and may
have a problem.
D13 - (90-150), mine is (165.4)
U4 pin 8 should be (-5 - -25) mine is (-28.9)
TP1 is at (0) as per spec.
J3 + lead should be (0) mine is (-38mv)

Are these acceptable before i move on??

Thanks for any info

Rick

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Nick Waterman]

Rick wrote:
> Hello all, I am to the point of the first voltage tests on my KPA100 and may
> have a problem.

I'm glad it's not just me. I have very similar symptoms and was about to
post about them... Did you get any answers yet?

> D13 - (90-150), mine is (165.4)

Mine also varies from about 155-170. It seems to do this periodically
too - it'll ramp up to 170 and hold, and ramp down to 155 and hold, then
ramp back up to 170 again. It's oscillating at about 1.5 - 2Hz.

> U4 pin 8 should be (-5 - -25) mine is (-28.9)

Mine's also varying from about -27 to about -30, and again it's looping
every couple of seconds.

> TP1 is at (0) as per spec.
> J3 + lead should be (0) mine is (-38mv)

Mine's also a tiny bit negative, but I figured a few millivolts is
probably "close enough" to zero.

I can see current varying up and down a bit at about 2Hz in the
"DISPLAY" voltage/current indication too.

I've also noticed that the above high values and 2Hz oscillations happen
only when I'm powered at 13.8V. If I drop the supply voltage a bit, the
values come down a bit and stop oscillating. They might match yours at
some point. If I drop further, to about 12V, they actually match the
"expected" values.

What supply voltage are the "expected" values specced for? What is the
"expected" behaviour if the supply voltage is raised a bit higher?
What's the highest acceptable supply voltage, and what might the above
readings be at that supply voltage?

> Are these acceptable before i move on??

Having discovered that my voltages match with a supply voltage of 12V, I
decided to keep the supply at 12V, and push on, and noticed another
oddity. My power transistors are photosensitive!

I noticed my fan was running as soon as I power up. I checked the "FAN
LoHi/Hi/nor" settings, but it was "nor". I discovered the fan DOESN'T
come on if my desk lamp was turned off. I checked "CAL tPA" and the
temperature would allegedly rocket well above 150C with the lamp on, and
a sensible 19C with the lamp off.

The lamp is warm, sure, but it's not roasting my hands and giving me a
tan or anything! I then tried with a tiny AAA maglite torch, and found
that yup, shine a bright light at either Q1 or Q2 and the "temperature"
rockets up. Shine almost anywhere else and it's fine. If I understand
right, Q3 is supposed to be the temperature sensor, but that didn't seem
to be so light-sensitive at all, it definitely required quite bright
light to be shone at either Q1 or Q2.

--
"Nosey" Nick Waterman, G7RZQ, K2 #5209.
use Std::Disclaimer;    [hidden email]
Everyone has a photographic memory. Some don't have film.
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com