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Hey, here is tom.
I serviced 2 7104 in the past and the story is still ongoing.
The first thing you have to do is to renew ALL coils and capacitors at the digitizer PCB and at the Y amplifier, check at ebay with SMD types. Most of the fails will disapear and you might come to a valid calibration. If only ONE module is defective you will just hear clicking relais at cal procedure.
NEVER turn any potentiometer andturntable capacitors because they are very critical to readjust. Tell me your results after theat basic service i told you. nice regards, tom
ok, this sounds good. Why. Built OUT all digitizer and Y ch 1-4, Choose only place ch4, ONLY put the digitizer and the Y ch in there and calibrate. do first the default procedure in cal menue. Then, in the cal menue see if you have high values, not more than 32000, if so hou have to calibrate DC and HF gain. Basically wait for warming up the Y ch to see if you reach the zero line, switching from GND to AC to DC in the 2mV range.(the Y ch is getting hot, dont worry, the relais are providing heat as most of them are activated) Hit the zero line key before. If there is no signifant moving when switching you can start a recal hitting the three buttons getting the cal menue. the cal procedure should not need more than 3 minutes for 4 ch. if he sees great values it will loop and loop again. also, on the digitizer change the 2 coils and all the caps !!! WHY ? These leaky capacitors hits down the supply voltage and are destryoing the DC filter coils, even when they loooks good. (measure the coil value in ohm, not more than 1 OHM is ok) good speed. tom
i think what tom was meaning was to resolder everything in the bad channels and see if that fixes the problem. if it doesn't, you can use the good channel as a reference for measuring voltages in the bad channels, because the circuits for all 4 are identical. when you begin replacing parts, a few will be in locations where it doesn't affect the calibration of the scope, but there are many components that will require recalibration, mainly any components in the signal path will affect the calibration. components outside the signal path (such as in the power supply) won't have much of an effect. you can do a rough calibration by using the known good channel as a baseline, and adjusting the repaired channels to match, but if you really need to know that what you are measuring with the scope is accurate, you should get the scope calibrated. maintaining traceable calibration standards is a bit too expensive and time consuming to be in the realm of the hobbyist (i have seen some people that collect old cal lab equipment, and some of them make the effort to maintain it, but as a hobby, that's a very small one, and usually the hobbyist also works in metrology as a career)