| Electronics > Repair |
| Aeroflex IFR-2398 / calibration / repair help |
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| andy_silicon:
Ignore my previous ramblings - the block diagram does fit :-) I'm looking in the wrong place. The 24db amp is a tiny 4 pin square device bottom right - after the 210Mhz bpf filter ( string of RC along the bottom ) and before the 3rd mixer ( white blob MCL device right hand side ) So the marking is hard to read 028 or 02B And I confirm that the board matches (more or less ) with the described bias conditions for this amp. 2 parallel 470 ohm resistors feed the bias from the 15v ( via an inductor ) So that gives 235 ohms over 15v - and assuming 3.7v drop across the mmic - thats about right. ( 11.75V = 235R x 50mA ) |
| andy_silicon:
Could the device for the 24dB amp be an MRF5711 ? http://pdf.datasheetcatalog.com/datasheet/motorola/MRF571.pdf The package style is correct , the bias current is correct , and the gain is correct. The noise figure is a bit better. |
| andy_silicon:
Like this - but with an 8 or B instead of an N. http://www.ebay.co.uk/itm/380067514769 |
| KJDS:
I don't think I've ever seen a 24dB gain amp fail in such a way that it became a 0dB stage. More usually when a MMIC or transistor amp fails it ends up with about 10dB of loss, so I wouldn't rely on the current loss as the fault finding mechanism. The good news is that there is enough signal loss that it would be easy enough to trace the signal through to find out where it's failing. |
| andy_silicon:
Seems a bit weird to me as well. The problem with fault finding is that the RF module doesn't work with the cover removed. I will have to improvise with some tin foil/copper tape. |
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