8970A的NF数值例如从-18.00漂移到+18.00并且连续上下移动

我购买了8970A，在+ 15v电源中有一个差的2400uf / 40v滤波器帽。
取下盖子，仪器活了起来。
我按照手册中定义的调整进行了操作。
一切似乎都很好，一切都在调整的范围内。
然而，在关闭仪器几天然后再打开它之后，存在一些奇怪的行为，我似乎无法找到根本原因。
当我第一次打开仪器时，它会校准和操作我通常会考虑的内容。
然后在大约20到30分钟后，NF和增益显示开始上下移动，这意味着NF的数值例如从-18.00漂移到+18.00并且连续上下移动（这些值只是一个例子，实际
值随时间而变化但效果相同）。
增益显示也是如此。
最终NF显示屏显示为空白并显示 - 但最终会自动返回。
然而，在未校准的自NF模式中，显示的值符合手册中的要求。
然而，该值也具有类似的恒定周期漂移但是更小，在0.5到-0.5范围内。
从-18到+18的漂移时间从峰值到峰值约为20到30秒左右。
最终，在大约2或3个小时后，显示器有些稳定，尽管它们从未保持为零。
我有另外三个8970，两个A和一个B，但没有一个表现出这个问题。
有谁知道这可能导致什么？
我看过（o'scope）所有电源，它们坚如磐石。
1750MHz LO确实漂移，最初约为2.5MHz，但它现在正好。
就像我说的那样，其他调整按照手册调整说明正常工作。
任何帮助将不胜感激！
-Bob Simpson



     以下为原文

  I purchased an 8970A that had one bad 2400uf/40v filter cap in the +15v power supply. Replaced the cap and the instrument came alive. I went through the box doing the Adjustments defined in the manual. All seemed well, everything was with in the range of the adjustments. However, after turning the instrument off for a few days and then turning it on again some strange behavior exists and I can't seem to find the root cause. When I first turn the instrument on it calibrates and operates what I would consider normally. Then after about 20 to 30 minutes the NF and Gain displays began to move up and down, meaning the numerical values of the NF for example drift from -18.00 to +18.00 and continuously up and down (the values are just an example, the actual values are different with time but the effect is the same). Same is true of the Gain display. Eventually the NF display goes blank and displays - - but will eventually come back on it's own. Yet, in the uncalibrated self NF mode the value displayed meets the requirements in the manual. However that value too has a similar constant periodic drift but much smaller, in the 0.5 to -0.5 range. The drift time from -18 to +18 is about 20 to 30 seconds or so from peak value to peak value. Eventually, after about 2 or 3 hours the displays somewhat stabilize although they never remain at zero. I have three other 8970's, two A's and a B and none of them exhibit this problem. Does anyone know what might be causing this? I have looked (o'scope) at all the power supplies, they are rock solid. The 1750MHz LO does drift and was originally about 2.5MHz off, but it is right on now. like I said, the other adjustments worked fine in accordance with the manuals adjustments instructions. Any help would be greatly appreciated! -Bob Simpson