I am looking at a 148 DX (late version with MC145106 PLL) for a friend of mine. It would not stay on frequency is why he asked me to look at it.
After a few futile attempts to "tweak it in" I replaced all of the electrolytic capacitors in it (they were all original) and gained a little ground on it. I then noticed that the binary adders had wires added to the solder side of the board and every front panel switch was "repurposed" for extra channels. After discussion with the owner, I removed all of the "extra channel jumpers" and returned all of the front panel switches to their original configuration.
I was able to get the PLL aligned and restored all of the proper (as designed) channels of all 3 bands. The AM receive is very weak (volume at max to hear static/hiss) but SSB is working fine. The radio transmits and receives SSB very well and has good sensitivity. AM does transmit on frequency.
It appears that the mode switch is OK as I measure 8.24vdc from the AM position pins of the mode switch with no shorts to other modes. I have measured transistor leg voltages per the Service Manual to no avail.
With limited equipment (VOM, RF Probe, Frequency Counter), is there anything I can check to attempt to return the AM receive sensitivity to this 148GTL-DX?
Any and all help is appreciated.
73's
David
After a few futile attempts to "tweak it in" I replaced all of the electrolytic capacitors in it (they were all original) and gained a little ground on it. I then noticed that the binary adders had wires added to the solder side of the board and every front panel switch was "repurposed" for extra channels. After discussion with the owner, I removed all of the "extra channel jumpers" and returned all of the front panel switches to their original configuration.
I was able to get the PLL aligned and restored all of the proper (as designed) channels of all 3 bands. The AM receive is very weak (volume at max to hear static/hiss) but SSB is working fine. The radio transmits and receives SSB very well and has good sensitivity. AM does transmit on frequency.
It appears that the mode switch is OK as I measure 8.24vdc from the AM position pins of the mode switch with no shorts to other modes. I have measured transistor leg voltages per the Service Manual to no avail.
With limited equipment (VOM, RF Probe, Frequency Counter), is there anything I can check to attempt to return the AM receive sensitivity to this 148GTL-DX?
Any and all help is appreciated.
73's
David