I didn't notice any amplitude changes on ch1 has I changed the scale on ch2, leading me to believe that maybe the relays are just routing the signal so I would need to find the final output where I see those changes take place. When I adjusted the vertical scale on ch2 where distortion occurs I could still see a clear square wave on channel 1. I ran the 5V probe signal into channel 2 on AC coupling and probed with channel 1 noticing the signal passing through all 3 relays just fine. Best to do this with another scope, but you can also do it by feeding the calibrator into your bad channel, then tracing the signal with a probe on the good channel. Another thing you can do is to trace the signal, see where it starts going sideways. From there you should be able to trace the path of connectivity through the other two relays. I'm guessing the DC block capacitor is to the right of the topmost relay on each channel. That relay ought to be bridging over the DC block capacitor when either closed or open. the BNC input should have connectivity with some pin or pins on the first relay. I don't get it - can you buzz out the signal path from the BNC input through the relays? E.g. Does the scope still behave the same way? Some relay contacts are allegedly self-cleaning, and may come good with usage, though I've never seen this happen. I can't see any problem with those measurements, and I'm guessing 0.2Ohm is your DMM's lead resistance. Well then - so much for my theory of dicky relays :/. I am wondering if maybe I have a bad hybrid, maybe changing the capacitors will help, or perhaps I have bad chips on the main board which I am hoping not! What do you think is going on? tds380_1 This is the scope itself tds380_2 When I power on the scope all the lights come on as normal and I hear relays clicking tds380_3 Every time this scope powers up I get this screen, calibration fail but at least power up passes tds380_4 I take at the calibration screen to notice the signal path failed but all other tests passed tds380_5 Taking a look at the error log I see calibration error relative amp gain, what does that mean? Also the memory read error is from the floppy drive tds380_6 Both channels show normal traces with no sources connected tds380_7 Both channels connected to the 5V probe pin, no problems here tds380_8 Both channels seem to work fine on ac coupling tds380_9 With both channels on dc coupling, ch 2 seems to have a dc coupling problem tds380_10 Here I am feeding both channels a 1kHz square wave output from a sound card in the good portion of the vertical scale, everything is fine tds380_11 When I adjust the vertical scale to the group of of bad settings, both channels seem to slightly drop out and show distortion tds380_12 and tds380_13 With the vertical scale set in the bad region and both channels connected to 5V probe pin, we again see abnormal results (both channels ac coupling) Other than these issues I have, everything seems to work perfectly fine. If I apply enough ac signal into ch 2 on dc, I start to get a signal but a distorted one. And to add, the dc coupling for channel 2 doesn't seem to work, I get a flat trace with either a ac or dc signal applied. In fact I don't know why I get a calibration error message because both channels seem to be measuring accurately. When I roll the vertical scale past this bad section, either lower or higher, everything works fine again. Basically what is going on is the vertical scale seems to have group of bad spots affecting both channels, the the input signal seems to distort and drop out. This is my first oscilliscope by the way. Hello I recently bought a used TDS 380 that is for the most part functional with the exception of some issues with the vertical scale and dc/ac coupling, I have attachments to show you what I mean.
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