| Electronics > Repair |
| Wavetek 2520a 0.2-2,200MHz RF sig gen repair |
| << < (18/22) > >> |
| dazz1:
Hi I replaced all of the Tant caps on the -15V supply plus the toasted one on the +15V supply. I didn't bother testing the removed caps, I just replaced them. After recapping the -15V supply was restored to normal. So that fixed at least two more faulty components. Now I am doing functional checks. The internal AM/FM modulation works fine. I just had to adjust the modulated signal amplitude. I connected an external AF sig gen to the modulation input and that doesn't work. The signal disappears in the circuit somewhere. Initial testing indicates the problem may be digital. A DAC is used to adjust the modulation level from 0 to 100%. This appears to be stuck on zero so the DAC blocks the modulation signal. The DAC is driven by a register with all output pins = low, so the fault is probably not the DAC. I need to do some more testing to identify the root cause. |
| dazz1:
Hi I did some functional testing today. The aim being to check that everything is working. All testing shown here was at 500MHz with a 0dBm output from the Wavetek 2520. The input of the spectrum analyzer was fitted with a Minicircuits 10dB attenuator to ensure a 50ohm load for the Wavetek output. This will have the effect of raising the RF noise floor seen on the spectrum analyser. The first image is a 500MHz CW signal looking from 0Hz to 2.1GHz There is one chirp above the noise floor, just to the left of the 500MHz signal. Zooming into the main signal at 500MHz with a 10kHz span. Looking more closely at the main output at 500MHz with a 1kHz span. The first peaks either side of the main output will be offset by the closed loop frequencies for the frequency control circuits. The images are supposed to be inline expandable thumbnails, but they aren't. |
| dazz1:
Hi Here is a the Wavetek 2520 output with internal AM modulation active. In theory, there should only two frequencies, one either side of the main output. The spectrum is messy but still useable. Note that the Wavetek and spectrum analyser don't agree on the frequency by 640Hz. I don't yet know which one is the most correct. |
| dazz1:
Hi The FM internal modulation produces a nice clean output when the Wavetek is setup for wideband FM modulation. |
| dazz1:
Hi I have proved that the internal FM/AM modulation functions work as intended. I still need to figure out why the external FM/AM modulation isn't working. |
| Navigation |
| Message Index |
| Next page |
| Previous page |