| Electronics > Repair |
| Wavetek 2520a 0.2-2,200MHz RF sig gen repair |
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| dazz1:
Hi I may have found the source of the next fault. The built in diagnostics routine for testing the DACs helped confirm that the DAC/OpAmp combination IC506 DAC1020 and IC513A 5532 shown on the lower part of the schematic are not responding to the digital inputs. The VCO drive voltage should range from 2VDC to 12VDC. I am seeing a constant 1.2 DCV. I am reading 0.7V DC across pins 2,3 of the Op Amp, which points to that being the failed part. I am going to look for a suitable op amp in my parts bin. That is the simplest, cheapest, fastest way forward right now. I have considered using the SSA as a sig gen but my main effort has been towards the digital and low freq (<10MHz) circuits. I haven't even measured the outputs of the 4x VCOs to see if they are working. The main reason I have been working on fixing the Wavetek 2520a is to gently exercise the brain as part of my recovery from a major road accident in Feb 21 that nearly killed me. That is also why it has taken so long to get to where I am fixing the 2520a. Doing diagnostics on some old test gear has been therapeutic. Dazz |
| dazz1:
Hi Achieved a major step forward today. I replaced a suspect op-amp that is between a 12bit DAC and the VCOs. The DAC sets the coarse control frequency in the main control loop. The op-amp outputs the VCO frequency control voltage. Another DDS loop sets the fine frequency. I also replaced a number of tant caps. The same type and voltage that have already failed. That should improve future reliability. After replacing the op-amp, the AutoCal routine No.19 for tuning the VCO frequencies passed. This proves that the Sig Gen is functioning. This does not eliminate a fault somewhere degrading the RF output. Next step is to do performance testing and calibration to prove full operation. Dazz |
| tautech:
Cool Dazz, your therapy is working ! :) |
| dazz1:
--- Quote from: tautech on June 02, 2021, 09:51:36 pm ---Cool Dazz, your therapy is working ! :) --- End quote --- Hi I know I am not operating within spec, but the Wavetek 2520a just might be. Dazz |
| dazz1:
Hi I connected up the Spec Analyzer and got a good output signal during AutoCal. I left the 2520a to run for a couple of hours to stabilize and ran AutoCal again. While I was running AutoCal, the output RF went to zero and the AutoCal routine failed. I have another fault but at least I know that it was working. The symptoms are identical to the previous fault so there may be a deeper issue. First thing I will look at is the power rails. It is possible that one of the many remaining Tants has released their magic smoke. Dazz |
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