Those with very good memories ( or who were even paying attention ) might think I'm spending an inordinate amount of time on this project. Truth is, although I posted about this months ago, I'm only now getting around to working on it, as with most of my projects. ( In the mean time, I've battled everything Mother Nature can throw at me while building a 2nd story 12'x24' deck for my home ) The problem was an intermittent disappearing trace on my old Tek 465 o'scope. I had suspected a problem with the triggering circuit, because I could sometimes make it work by fooling with the front panel controls. I was very lucky to find a manual online to download, and I printed the schematic portion from it. I set up the Tek to be diagnosed with a good scope I have, a B&K precision 2120B (see photo) the Tek is connected to the 2120B's calibration output, and that trace is shown on the "bottom" trace ( or right trace and the traces are vertical in the picture ) The 2120B is showing the negative going sweep signal that is generated by the Tek in response to the trigger signal, which is in turn generated from the 2120B's output. Also, the "top" or left trace on the Tek is the trigger signal. I had to use the Tek to scope its own trigger signal, as this is a very high impedance signal, and the higher capacitive probes of the 2120B kills it.
3 days into the experiment, and the Tek has yet to exhibit the failure. But it's all good because it allows me the opportunity to probe all the relevant signal while they are "correct." My suspicion is somewhat confirmed, however, because I can see signs of previous service on the same circuit. There are some suspect solder joints, which could cause the problem I've been seeing. I might just touch up the soldier, slap the case back on and call it a day.
The Tek is a nice instrument, and it's good to have a circuit which can actually be analyzed and diagnosed. The design is elegant and straight forward. They use a cleaver way of arming/firing the trigger, which uses tunnel diodes as memory elements to make a sort of state machine. I was thrown at first about how this part of the circuit operated, but the manual has a real nice theory section, and I was able to figure it out.
Well, the next rainy day, I'll try the solder iron repair and put it back together. Going through the schematic, I realized if the problem returns, I can isolate it a certain degree by switching over to the delay trigger, as it uses a similar, separate circuit to generate the trigger and sweep. Hopefully, I'll get many more years of service from the 'scope.
3 days into the experiment, and the Tek has yet to exhibit the failure. But it's all good because it allows me the opportunity to probe all the relevant signal while they are "correct." My suspicion is somewhat confirmed, however, because I can see signs of previous service on the same circuit. There are some suspect solder joints, which could cause the problem I've been seeing. I might just touch up the soldier, slap the case back on and call it a day.
The Tek is a nice instrument, and it's good to have a circuit which can actually be analyzed and diagnosed. The design is elegant and straight forward. They use a cleaver way of arming/firing the trigger, which uses tunnel diodes as memory elements to make a sort of state machine. I was thrown at first about how this part of the circuit operated, but the manual has a real nice theory section, and I was able to figure it out.
Well, the next rainy day, I'll try the solder iron repair and put it back together. Going through the schematic, I realized if the problem returns, I can isolate it a certain degree by switching over to the delay trigger, as it uses a similar, separate circuit to generate the trigger and sweep. Hopefully, I'll get many more years of service from the 'scope.
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