Re: 7A26 no signal


 

Do you have a service manual for the 7A26? If not, here are PDFs of the manuals http://w140.com/tekwiki/wiki/7A26

Looking at the images of the 7A26's insides it should be easy to trace an input signal from the attenuators through the amplification stages and then to the backplane, assuming that you can connect the module to the backplane in a way that allows you to access the insides (I assume that there are extension plugins that let you run a plugin outside the main housing, though I can't find reference to such a thing on TekWiki).

I did something similar with a 475 a few weeks ago, and tracing the signal was quite simple to do, given schematics and board layouts, and a second scope to test with. In my case the issue was an unseated channel switch IC, and tracing the signal through channel 1 lead me straight to the problem.

Looking at the images it doesn't look like the 7A26 has the channel switch that the vertical system of a 475 has (I assume that's located in main unit), which means that the common failure must be elsewhere. The obvious places to look are where the signals exit the plugin, and where power enters the plugin, but you really need to see how far the input signal gets through the amplification chain to make any real diagnosis.

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