| Electronics > Repair |
| Tek 2445 issue with CH2 |
| (1/1) |
| giosif:
Hi, Recently, I got my hands on a broken Tektronix 2445 scope which, at first didn't even power up. With help from people on this forum, I was able to fix the PSU and the scope is now turning on. However, CH2 has an interesting problem, where the signal I feed into it is showing at 50% vertical amplitude from the expected value. That happens with the channel set in DC coupling mode. In AC mode, the signal is displayed with the correct amplitude. Also, in DC coupling mode, the resistance I measure for the CH2 input is infinite, while CH1 is measuring the expected 1 MOhm. Looks to me I need to remove the CH2 attenuator assembly and check for any issues there. Would you agree or do you think I should do some other checks first? Thanks! |
| m k:
You can also check different termination and attenuation modes. Since AC is ok upper side of 1st and 2nd switches are ok. For lower parts you can check calibrator input, 0.2V for DC coupled 50 ohms load. If removing an attenuator is not a punishment you can also swap them and be sure. |
| giosif:
Thanks, m k! In the meantime, I decided to remove and disassemble the attenuator from CH2. I then proceeded to clean the contact pads on the ceramic substrate which make contact with the relay "fingers" (I very gently scratched the pads with some tweezers and under the microscope). I also cleaned the relay contact "fingers" using IPA. I reassembled and reinstalled the attenuator and now CH2 is working great. :-+ |
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