OK, by way of an update, TX is fine into a dummy load. I've visited a friend today using their tribander and exactly them same problem on RX though SWR is fine, flick to the same antenna on there FT1000 and there's not a problem RX or TX.
Unfortunatly I don't have access to a sig gen, I have tried connecting the antenna and then checking the boards for flex or loose connections with no joy.
All those jumpers are fine and doing a great job?
Really no further forward..
OK, this is getting fairly strange.
Just to re-cap: On dummy load transmitting is OK?
Then when you go to a friends house with a "known good" antenna the receive goes dead when connected to an antenna that the normal station rig uses OK?
If that's the case then we know only one fact: The problem, whatever it is, is in the 706.
That is only one step towards fixing it.
My706 started exhibiting strange behavior with fluctuating SWR and power out on VHF which was eventually traced (not by me) to a cold solder joint on the VHF final.
Not that it has anything to do with your problem...
I'm out of ideas, mate.
Maybe someone else?
Open up the 706 and locate the MAIN UNIT (MAIN 1) and disconnect P1 from J101.
Connect the antenna shield to the chassis of the 706 and connect the center conductor of the coax to CP101.
See if the reception returns. If so then you have a problem in the FILTER UNIT. If not then it's farther down the RF path but shouldn't be too much farther then this point.
Make sure you have a dummy load connected to the usual antenna jack or disable the transmit so you don't accidentally transmit into an open.
Service manual here at; http://www.repeater-builder.com/icom...ice-manual.pdf and the information is on page 10-2. The FILTER UNIT is later in the manual.
Wait a sec....could be the wrong model. Look at this service manual and see if it's the correct one; http://www.repeater-builder.com/icom...ice-manual.pdf.
If so then you need to disconnect P1 from J1 and connect the antenna to the jack J1 (page 11-2). The earlier models of the 706 are a bit more difficult to work on as far as test points are concerned.
Anyway, see what that does.....
Get back to us with the results.
Hope this helps
Last edited by KO6WB; 09-08-2013 at 02:42 AM.
Originally Posted by KO6WB
Tried exactly what you suggested and the fault is still there when the antenna is connected to J1...
Not sure if you are having the problem with or without the pre-amp enabled. If the pre-amp is on then apply the antenna center conductor through a .01ufd blocking capacitor to pin 6 of IC1 (uPC1658G).
Also check the voltage at the top end of R7 and make sure the pre-amp selection voltage is within specification. See if that helps.
Also, what is the s-meter reading when you're using the antenna? Could be something overloading the entire frontend and causing the receiver to simply blank out.
Originally Posted by KO6WB
Pre-Amp and ATT for that matter are functioning perfectly. I don't think there are issues with overloading, the S-Meter reads as it should in terms of RX.
Strong Broadcast Station
+60 with Pre-Amp to the point of overloading
S7 without no overload
Connect the sheild
S0 with Pre-Amp just about readable
Nothing without preamp
Connecting the chassis to the PL259 shield without it being connected to the SO
With preamp S7???
I hope that makes sense? To summarise, the shield of the PL connected to the shield of the SO drops from +60 to 0, the shield of the PL not connected to the SO but bridged to the chassis drops +60 to S7. The anttenuation is not as severve when the PL is bridged to the chassis rather than the SO
R7 - Whereabouts?
Last edited by M3BPK; 09-09-2013 at 08:57 AM.
My eyes are really getting old.....Sorry, R7 is for the selection of the appropriate band filter, so just ignore the goof up.
The voltage is at the cathodes at the junction of D12,D13 and looks like D28.
It could be there is a filter being selected when it shouldn't be but darned if i can figure out how that'll cause this problem.
Here's the area I'm looking at and remember....Old eyes......
Hope this helps some but it's a head scratcher for sure.