| Electronics > Repair |
| TDS3014 adventures |
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| giosif:
Just wanted to thank James, as well as the other contributors, for the nicely detailed repair and mods here, as I just brought a seemingly dead TDS 3034B back to life. The culprit? The same 75.757 MHz crystal which had stopped oscillating. New replacement crystal ordered (currently using a 50 MHz one I happened to have in the spares box). Now, on to the next issues: acquisition test fails and channels 3 and 4 seem to be "linked" with each other (i.e. if I feed signal straight into channel 4, I don't get any waveform displayed for channel 4; if I feed the signal into channel 3, I get the same trace displayed for both channels 3 and 4). |
| james_s:
That's an odd one, there must be some kind of mux? Hopefully it's not inside one of the ASICs. |
| giosif:
I suspect the same, but I need to do more investigations. Will report back any findings. |
| james_s:
Put the proper oscillator in there first before you expend TOO much effort. I doubt that's the issue here but it's not impossible. When I put the 27MHz oscillator in mine for testing it booted up but it was not usable. It's possible that the multiplexing is dependent on the timing. |
| giosif:
That did cross my mind but, then, strange it would happen only with channel 4. As you say, it's unlikely that is the culprit but I'll check once I've installed the correct crystal. From another perspective, I was wondering how it could happen that signal fed into channel 3 shows up for channel 4 as well. From an analog input perspective, it can't happen, since each channel is independent all the way to the ADC, including. From a digital point of view, the ADC shouldn't matter (as in, whether it is working or not), since each channel has their own. So, the problem must be with storing/retrieving the waveform data to/from memory. Specifically, I'm thinking that maybe one address line might be stuck either high or low and, whenever the memory range for channel 4 is being addressed, it ends up accessing the memory for channel 3. |
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