Maxtrac Receiver Adjustment - Low Sensitivity

[fireradio]

Hey all -

I just finished swapping out logic boards on some Maxtracs to get a low split, low band Maxtrac with full signaling support. Of course, I recorded the tuning values from the RF board prior to installing the new logic board, so I put the old values back in after replacing the board.

Transmitter looks great -- only 40 Hz off frequency... however, the receiver is a bit deaf... -100 dBm barely breaks squelch, and its completely silent at -110 dBm.

Not having worked on Maxtracs in depth before, I was wondering if there's any way I could improve the RX sensitivity.

Note: I am using the proper RF board for the frequency range I need - not trying to do any squirrelly out-of-band stuff here. I don't have access to the service manual right now, but I'm doing my best to come up with a copy.

Thanks for the help.

[PETNRDX]

Did you blank the board completely and "not" save the tuning values?
Sounds like that is what you did, and that IS what you should do.
The only thing I can think of is that the VCO steering voltage could be off if you moved very far in freq from where the radio was before.
Usually the Maxtrac is pretty "pliable" and will move all over with few issues.
The steering line really likes to be between 2 v and 7 v.
Check that as a start ( Both TX and RX ).

[kcbooboo]

There's nothing in the initialization procedure that affects the receiver. It seems as if yours has lost about 20dB of sensitivity. A common problem on GM300s is a shorted protection diode on the input of the receiver, usually accompanied by a blown out RF amplifier transistor immediately after it. Fairly easy to replace and Motorola can supply both parts but they are about $3 each.

Bob M.