[Premium-Rx] Racal 9400 reference osc "jumpy"

[Karl-Arne Markström]

The Racal 9400 is prone to component ageing, especially when in continuous 
operation.

Most cases are the parallel capacitor C1 across the trimmer, and in some 
cases the feedback capacitors in the Colpitts oscillator circuit.

Even the crystal itself can be aged so it shows "jumpy" behaviour.

I have sent a schematic scan to Stein-Olav via PM.

73/

Karl-Arne
SM0AOM


----- Original Message ----- 
From: "Stein-Olav Lund" <stein.olav.lund at hist.no>
To: <premium-rx at qth.net>
Sent: Tuesday, April 14, 2009 1:17 PM
Subject: [Premium-Rx] Racal 9400 reference osc "jumpy"


> Hello,
>
> I have an older VHF transceiver tester from Neuwirth which uses a Racal
> 9400 reference oscillator at 5 MHz.
>
> I discovered that the built-in frequency counter was off by around 12
> ppm, and as I measured the output
>
> from the ref osc (with a calibrated Fluke 1900A) this was also off by
> the same amount.
>
> The 9400 has a hole for a trimmer tool, but as the freq sometimes seems
> correct, I am reluctant to "twiddling" the adjuster.
>
> Are these oscillators possible to open for repair without destroying
> anything? Any tips are welcome.
>
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