So I have lots of anaog Tek stuff. Highly refurbished and upgraded 7904s and I think most every plug in. I have most all of the TM500/5000 stuff I will ever need. Mostly this stuff worked right away off ebay and then I would refurbish and make near new. Service manuals make this easy. Well,, except for the occasional custom IC,, everything I bought got fix and I have in my lab in use.
BUT I needed a digital scope.. No prob I thought.. Just grab a TDS3012B for fairly cheap off ebay. These are way newer and not much to fail.
Wow was i wrong... You guys should let me know if my luck is just really bad or do these scopes have serious failure rates ?
First scope looked great. Self test perfect. Calibration perfect. Everything worked except one knob had issues. I expected a knob issue after researching and knew how to fix it. So this was great.. UNTIL I let it run for 40 mins.. After warm up the front panel controls died and the LEDS all flashed.. It worked in every other way. I could control it via IEEE or e-scope. Just lost complete control from the front panel. After exaustive work, its something on the main board. Not power supply as all voltages on the main board at the chips involved are fine. I also swaped supplies. I swapped front panel boards. Nope. Its the main board and its complex as its something going on on the data lines to the front panel and these are hard to probe close to the CPU chip. It could be the CPU is wonky.
So that main board is pretty much hopeless..
So I bought another one, they said fully tested. Indeed when i got it I fully tested and it was great.. In calibration... BUT THEN.. about 15 mins of on tine and dense positive going spikes appeared on the waveform with no input that were full scale that caused triggering and measured full scale even with no input. Both inputs. ONLY ON SCALES ABOVE 1V.. 500mv and down is perfect. Again its a thermal issue and easily missed with a quick check. Not the power supply. Its obviously a complex main board issue that might even be a ADC chip set issue.
So I am batting 0 so far.. 2 junked main boards.. I was able to clean up 2 front boards tho. I got removing and cleaning the rotary encoders down great.
So I now have a 3rd unit coming. This time from someone who knows these scopes I am talking to about these issues. So hopefully the 3rd is the charm..
So no schematics ? No one has come up with anything ?
Are these things really that bad ? Are there lots of main boards in the trash ? Anyone have one they know works they might want to sell me ?
Sorry for the rant..
