MSF5000 fails to transmit

[n8xpq]

I have a digital capable 70cm UHF MSF5000 that suddenly failed to transmit. There are not any error codes displayed. he receiver seems to work properly. It will not TX from received signal, front panel TX switch, or the front panel mic jack. It seems to try to TX for a split second, then reverts back to RX. I have checked the connections on the Uni board to the PA and they are good, the PA has supply voltage. Does anyone have any ideas what I should check next?

Thank you

Mike

[Doug]

First of all let me say welcome to the board. I'm afraid a little more information is required. Is the station running internal filters or an external duplexer. Is this a new setup or has it been on the air for a while. The transmitter keying is dependent on the feedback voltage coming from the circulator in the amp, too much reflected voltage will cause the station to act as it is. I've also had them doing the exact same thing when the power output resistor on the front of the station has gone bad. I would first try and lower the output as low as it will go and then try keying the station and see what happens.
Doug

[d119]

I have a digital capable 70cm UHF MSF5000 that suddenly failed to transmit. There are not any error codes displayed. he receiver seems to work properly. It will not TX from received signal, front panel TX switch, or the front panel mic jack. It seems to try to TX for a split second, then reverts back to RX. I have checked the connections on the Uni board to the PA and they are good, the PA has supply voltage. Does anyone have any ideas what I should check next?

Thank you

Mike

Also, there is a molex connector between the PA and the station RF tray (controller). Make sure that's plugged in, or you'll get those same symptoms. Same thing if the PA is missing, or not powered up.

[wa6ylb]

I have a digital capable 70cm UHF MSF5000 that suddenly failed to transmit. There are not any error codes displayed. he receiver seems to work properly. It will not TX from received signal, front panel TX switch, or the front panel mic jack. It seems to try to TX for a split second, then reverts back to RX. I have checked the connections on the Uni board to the PA and they are good, the PA has supply voltage. Does anyone have any ideas what I should check next?

Thank you

Mike

Check the three pole exciter filter, under the PA, on the left side. Its a exciter to PA filter. If its slightly off, there won't be enough power to drive the PA. (hence the split second transmit)
The tuning screws are silver plated, and tarnish after awhile. Notate their original position and rock them back and forth a bit to cause them to clean the oxide on the threads of the screw.
Alternatively, you can disconnect the output and then meter it to peak the power from the exciter. Its rather broad in tuning.
B.