Need help with a GR1225 repeater

[mcx1000]

Received via e-mail from a fellow club member:

The 145.21 receive is -96dbm. I need a service manual or experienced in receiver adjustment on the 1225. I do not want to open and guess.
GR1225 Motorola. I think it is the same as GM300?? not sure . I was planning to install Thursday evening . Al and myself were going to drive up.
I will home tonight and Wed night working on it .

What is the receiver section based upon? I assumed it was built from M1225 radios, are these similar to the GM300/Radius type radios?
Any info would be appreciated.

[Will]

The GR1225 has one radio, a R1225, in it. The R1225 radio chassis is a whole different radio, designed from the ground up to be a repeater.

Sometimes the RF amp in the receiver goes bad. This is all surface mount construction.

[chartofmaryland]

The 1225 has a separate RX port from TX so the PA failing would not cause the RX to degrade.

Below 146 Mhz the performance does cut some, .45 instead of .3 uv but not 4.0uv.

It does sound like a component problem. All of this is SMD and most of the components are very small.

If that does not stop you then find a manual and you should find your problem.

1 note, there is a clamping Diode CR1 which limits the drive into Q1 the first amplifier, if you find this blown or shorted, then you may have an isolation problem with your duplex setup.

I've replaced a few too many of these from other peoples work.


CoM