Hello:
I've been trying to repair my osciloscope, it's not a well known brand but it's fully discrete and the circuit is similar to a tek 465. The problem is that i can't see square signals, they are very distorted on both channels. I tried to follow the signal with another scope but didn't get far, because my readings didn't show a similar signal to what was displayed and maybe because i don't know how to properly measure on a diferential amp. I tried the trick of shorting the transistors shown on the tek guide on how to repair scopes and it didn't help me, and i tried replacing the diode switches with new ones and isolating each chanel but could never reach a conclusion.
I'm lost.
I made a test circuit to get some reference signals: a 20MHz dip oscilator module (8 pin metalic can) feeds two 51 ohms resistors, that go through 20cms of rg174 coax into a bnc male that goes into a bnc tee were the other ends go to the osciloscope input and to a 51ohm resistor. This circuit displays the"20Mhz" pics.
I also probed with a X10 osciloscope probe a board that has an 74hc74 flip-flop clocked at 16MHz and got the "16MHz" and "8MHz" pics, these last one didn't come out the same because i had to capture the event but it shows the ringing at the rising and falling edges. For the osciloscope probe i used a tiny (1cm) piece of wire from the tip ground to the ic ground pin, not the usual ground clip.
The pics are at:
Osciloscope history of repairs that i made was a bad bridge on the power supply (intermitent open diode) and a logic chip that togles the chanels in ALt mode.
Any help/pointer are apreciated.
Thank you
Best Regards
Steve Sousa