[R-390] Repair of Crystal Oven for 1.0 Mhz Calibrator Crystal

[nryan at mchsi.com]

Hi, Paul and group,

The likely cause of failure in the crystal oven is corroded wiring inside.  The wire usually is braided untinned copper and apparently the solder flux used on it has eaten through the connection.  Open up the oven, take the crystal out and I think you will see what I'm referring to.

I haven't found a way to repair crystal ovens easily, so I just reach for a working oven and place it and the crystal back in service.  Replacement ovens are easily found at hamfests, but take your multimeter along for continuity testing.  You do want the oven to heat your crystal so that it may work at its specified frequency.

73 de Norman, KG4SWM


----- Original Message -----
From: Paul Dulaff <pdulaff at embarqmail.com>
To: r-390 at mailman.qth.net
Sent: Mon, 23 May 2011 15:25:50 -0500 (CDT)
Subject: [R-390] Repair of Crystal Oven for 1.0 Mhz Calibrator Crystal

Everyone

I am repairing an R390 and I am having trouble getting the calibrator signal adjusted precisely beating with WWV at 10.000 Mhz as the adjustment runs out of range. I found that the oven for calibrator crystal is not working and may be keeping the crystal frequency low. I suspect the thermostat is not contacting.

Has anyone been able to open the thermostat and clean the contacts ?

Best 73's

Paul - WB2NMI