7A12 attenuator board clone

Martin Hodge

Last year I was lucky enough to find a Tek 7704A scope on CL for free! The scope came with 7A12 and 7B523A plugins. Wanting a 4 channel scope I found another 7A12 on eBay but it turned out to have a broken attenuator board on channel 1. These boards are made of some kind of transparent, rock-candy-like material and are extremely brittle. This one had cracked and separated several traces. I jumped the traces with thin wire and got the board working again. The traces were to two of the relay magnets, no signals running through them. But in the process of unplugging and re plugging the board, one of the connector mezzanines crumbled into several pieces. Something came over me at this point and I decided to waste a lot of time building a new board using modern FR4 process. The photo album linked below shows the process. I was going to make another for channel 2 out of Robertson material and run a comparison with FR4, but before I even priced a board at pcbway I realized I didn't have a signal source with a rise time fast enough to test with. In the end I grew to dislike the 7A12 for it's overly complicated internals, sticky buttons, and meek performance and got rid of them. Though I did like the front panel layout.

(Be sure to read the photo descriptions for more info)

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