R2550 (R2600) Ant Input Reading Low (not BNC fuse) Problem

[Mike Peterson]

Hi,
I have a R2550 (about the same as the R2600 I think) that is reading about 12-15 dB low on the measurements for the Antenna Input jack. Mine happens to have the tracking generator option and when tuning duplexers I have to throw a little amp on the antenna input to give it a boost of sensitivity. The antenna input fuse in the BNC connector is good (first check on this unit). Anyone dig into this part of the monitor and have any advice? I don't have a schematic and have been looking at buying a jpeg manual that is out there from China to try. Unless if anyone knows where you can get a PDF service manual? That might be a bit better copy than a jpeg one. Thanks an d any input would be appreciated!

[jry]

You may want to verify the continuity of the cable from the FP ant jack to the SMB that goes into A8 J1 ( RF input module ). Often times the fuse is good but the connection is bad.

Is the input level correct from the RF i/O connector ....there is a pad in between so the R/F I.O.so it does take a higher signal. ( 30db IIRC)

Do the 20db and 40db attenuator levels work correctly ?.

If the level from the RF i/O connector is correct and the 20 and 40 db attenuation works than you may have bad /shorted input protection diodes or a bad RF switch IC .

You would have to pull the module and test the diodes since it's DC blocked from the FP ant connector J1

[Mike Peterson]

Thanks for the info jry. I will check in that direction. Yes, if I remember right, the 20 and 40 dB attenuator works. I'll post my findings when I get into the unit. Thanks again!

[jonnyc]

Did you MEASURE the fuse, or just look for an indication of continuity?
I once had a similar prob and when I suggested a high res fuse I was laughed out of court by all the cognoscienti.
But when i measured it, ..............51 ohms! Replaced fuse and prob gone!

JC

[Mike Peterson]

Interesting on what you found one time JC. I did a continuity check on it with a meter and it was good. I did dig into it a couple of weeks ago and injected a signal into the module and same problem, low measure for the RF input. Now I have to try and do a some digging into the module. Looks like it could be a bit of work to service the board. Been busy with radio work so not much time lately with my own stuff on the bench as this is a farming area up here and they are keeping me busy. I'll do a post on my findings when I get a chance to try and do some further trouble shooting. Thanks for the note!