At cold start, with 0.1us selected, the output checked 9.9981MHz. After about a 90 minute warmup, the crystal can is warm to the touch, cycle time is much longer, and the output still checks 9.9981MHz. I was going on memory that the output frequency was 9.999x and that's incorrect.
I'll have to check the components as well as the interaction of L9. I think I adjusted that for uniformity of the markers but I don't think I tried checking to see whether I can reach a compromise between L9 and C8 to get good results for both frequency and marker uniformity.
Thanks,
Barry - N4BUQ
toggle quoted message
Show quoted text
----- Original Message -----
From: "Eric" <ericsp@...>
To: "tekscopes" <[email protected]>
Sent: Monday, December 6, 2021 11:55:53 PM
Subject: Re: [TekScopes] 10Mhz under frequency in 184 Time-Mark Generator
How long a warmup time are you giving the crystal before trying to cal.
Also how is your probing set up? This circuit is incredably sensitive to
capacitance. Not enough heat in the crystal and or too much capacitance in
the probing set up will drag the crystal off to the low side of things.
Eric
On Tue, Dec 7, 2021, 12:41 AM Jeff Dutky <jeff.dutky@...> wrote:
The advertised spec is +/- 0.001%, so (if my math is right) you are will
within the advertised precision.
The circuit in which Y11 operates looks pretty simple, the only components
around it are C11, R11, L18, and V10. I'd have a look at R11 to be sure it
hadn't drifted (the parts list seems to indicate that it's an unremarkable
carbon comp resistor, with 10% accuracy). You could also remove the
Nuvistor and the crystal in order to check C11 in place. I expect that both
V10 and Y11 are socketed, but I can't really tell about the crystal oven
from the pictures in the service manual, so it might be easier to unsolder
C11 than to remove Y11.
-- Jeff Dutky
