| Electronics > Repair |
| Aeroflex IFR-2398 / calibration / repair help |
| << < (4/16) > >> |
| andy_silicon:
Nope - with the cover off - all self tests fail - no YIG The YIG is in the RF module - and I suspect without the cover it swamps everything. I tried replacing the cover with TiN Foil :-) , but same result. I could remove the part and bypass it ( to see if we lose more gain - or it remains the same ) but I may as replace the part. KJDS - any suggestions/experience in debugging such units ? I suppose I could use some thin wirewrap to connect the bias network to an external variable resistor ( 200-700ohms) - then I could vary the resistor to see if the device is working as it should. |
| KJDS:
Clamp an aluminium sheet with a 1cm hole in it over the housing to act as a lid. Move it so that the hole is positioned over where you want to probe. Check with a scope that the voltages are ok on each amplifier. A multimeter probe can cause an RF gain stage to oscillate. Make up a probe with a 470R resistor on the end of some thin coax. This, when probing a 50R system gives you a 20dB passive probe that won't have much effect on the circuit being tested. With care then this can work ok up to about 3GHz. If you bare the end of the coas so it touches the lid then that will give an ok ground path. A 24dB fault should be easy to locate, it's hunting down the missing 2dB as that sort of circuit is being designed that's the real pain. You can check most of the circuit if you've got a fast scope, which will just leave the first IF to check, assuming that it's not an LO driver faulting causing high mixer loss. |
| andy_silicon:
Well - I have enough appropriate test equipment :) - but there is no way to be able to clamp an aluminium sheet in place ( the RF module plugs into a motherboard - and there is no space. A full disassembly of the chassis would be required ( the module is between a support and another module ). I may have to prepare an aluminium sheet of the exact size with some of the screw holes in place. Then solder a 470R in place and feed through a hole - attach the sheet - solder the coax - put the module in place. Thanks for the 470R tip. |
| andy_silicon:
Minor update. I managed to get the unit apart enough to do some probing of the RF section. ( and shield the Yig enough to get Yig lock ) The calibration signal is verified at -30dBm as it enters the attenuator chain. By the bottom of the chain it's a couple of dB down. After the low pass filter and first amp it's back to -30dBm for input to the first mixer ( a minicircuits MCL-1 ) The 1st seems to be somewhere around -10dBm to 0dBm ( difficult to measure with the probe ) After the first mixer I'm having trouble reliably monitoring the cal signal - will try again later. |
| andy_silicon:
I'm beginning to suspect a bodge on the input to the 1st mixer. There is space for a single smd ( probably an R ). However three components have been soldered to the board in an hf boost filter. ( R in parallel with C and this combination in series with an R ) If the C has gone bad , it might explain the reduced gain and overall HF fall off. ( about 30-40dB down at 2.7G compared to 40Mhz ) |
| Navigation |
| Message Index |
| Next page |
| Previous page |