Please forgive me for wandering off on a tangent during this fascinating discussion on audiostoopid but I actually spent a couple of hours at my bench today working on
test equipment.
![Roll Eyes ::)](https://www.eevblog.com/forum/Smileys/default/rolleyes.gif)
I replaced the Tek power plug on the 184, which is a right pain in the ass, with a power cord, and no longer have to look at this:
![](http://u.cubeupload.com/worsthorse/IMG1042.jpg)
Letting it warm up for two hours
![Scared :scared:](https://www.eevblog.com/forum/Smileys/default/scared.gif)
as suggested in the service manual, I was pleased to find that the local oven-ized 10MHz oscillator running at a steady 10,000,032 Hz and drifting no more than +/- 1Hz. While that is well within spec, we will see if we can do better a little later. And to be honest, the oscillator was running at that frequency within ten minutes of turning it on and didn't move after that.
First thing I found was roughly 200mV of 10MHz ripple on the DC rails (12, -30, 125). This is a good bit higher than it should be, if I am reading the specs correctly.
Then I worked my way through different combinations of markers. At 1us and longer, it puts out a good signal:
![](http://u.cubeupload.com/worsthorse/TRACE3.png)
But at 500ns, things start to look not so good:
![](http://u.cubeupload.com/worsthorse/TRACE1.png)
Same for mixed markers (500ns and 100ns):
![](http://u.cubeupload.com/worsthorse/TRACE2.png)
The top trace is the marker output channel, the bottom the trigger output channel.
It is not surprising that there's cross talk here, nothing in the box is shielded:
![](http://u.cubeupload.com/worsthorse/IMG1014.jpg)
![](http://u.cubeupload.com/worsthorse/IMG1016.jpg)
There's also a little 500MHz filter board on the side and in the open that I didn't photograph. I have to check the manual, but I would guess that the crosstalk is small enough that it would meet spec. But even if it is, the marker output below 500ns isn't right and needs to be addressed.
I will start by looking at the power supply more carefully tomorrow and see if I can clean it up. It has been a while since I worked on anything generating frequencies like this...