Randy Downs wrote:
Thought I found the problem....THEN I put the top back on. It failed
when the fp temp got to 37 deg c. If I leave the top off it won't
fail. The fp stays at 34 deg c. It's thermal whatever it is.
Randy,
Coincidentally, I just e-mailed you tentative instructions on how to
fix this. It takes one resistor. Please give it a try.
I discovered the problem Friday night. In rare cases, VCO operating
current may be inadequate on the highest bands once the rig has warmed
up. This can be cured by increasing the nominal current supplied to the
oscillator JFET (Q1). To do this, R10 is reduced in value from 82 K to
about 56 K.
Here are the rough instructions if anyone else needs them now (or you
can wait for the official modification doc):
1. Turn off the K3 and remove the affected KSYN3 module. (Note: If you
saw ERR PL1, it's the main synth; ERR PL2 is the sub synth.)
2. Locate a 1/8-watt or 1/4-watt 180 K resistor (or any value from 150
to 200 K). Solder it on the top side of the KSYN3 PC board, between the
pad marked "DET" and the pad closest to it (going in the direction of
J83, not the pad labeled "G"). [Photo to be supplied in the
modification doc.] Technical note: This resistor will be in parallel
with R10, resulting in a value of around 56 K rather than the original
180 K.
3. Re-install the synth board and turn the rig back on.
4. Make sure your K3 firmware is at rev 2.73 or later. If you haven't
adjusted the CONFIG:ADC REF menu parameter, do so now, using the
instructions in the revision 2.73 firmware release notes (accessible
from within K3 Utility).
5. Re-run VCO CAL (remember to tap SUB within the VCO MD menu entry if
you're calibrating the second synth).
This change can be safely made to any synthesizer module.
73,
Wayne
N6KR
---
http://www.elecraft.com
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