More 1S1 fun...a closer look at tunnel diodes and power supply ripple

Sean Turner

Back at studying my prototype 1S1. I've been systematically studying the circuit descriptions and schematics in attempt to figure out how it is supposed to work. Another potential trouble area I have identified is in the comparator circuit in the fast ramp generator. Specifically, there are a pair of 4.7 MA tunnel diodes that are part of this circuit. Specifically, D345 is supposed to control Q344 depending on what state it is in. However, the curve for D345 does not look much like a tunnel diode to me. I've uploaded a picture of both curves to ( leveraging my 577D1 to overlay them. It seems to me that D345 might be stuck 'turned on'.

Another problem I have noted during live troubleshooting is that there is still severe 120 Hz ripple appearing all over the circuits of the plug-in even after replacing the extremely crusty 100 uF filter caps on the + and -19V rails. It's about 200 mVpp, and shows up on the vertical signal out, the dc offset out, and to a lesser extent on the horizontal out. It also shows up at many of the suggested test points in the troubleshooting steps. I'm about at wit's end trying to figure out where it is coming from. It is worth noting that I am running the 1S1 using a Type 81 plug in adapter in my 585A. I believe it should be compatible though...and I have other plug ins that work fine on the same adapter!

Any ideas are much appreciated.

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