Sears RoadTalker 934.38260700 Dead... :-(

[Justin B.]

Hopefully somebody can help me with this or tell me it just needs to go into the scrap bin!

I picked this up a couple of years ago and stuffed it into the "someday" pile. The someday pile is nearing the end so I pulled it out the other day and started messing with it. Lights work, slight background hiss out of the speaker but no change when attaching antenna. Hooked signal to antenna input, set channel selector to multiple channels and adjusted sig gen output accordingly - no signal. Luckily I had a Sams for it (thanks Dan!) and started in on the alignments. The first step is to verify the 10.240 MHz signal at IC701, pin4 - no signal. I figured maybe a wonky crystal so I hooked my sig gen across it and injected a 10.240 MHz signal and the radio is still dead.

IC-701 is a SM5104 G PLL chip and maybe the chip is bad and and keeping the crystal from oscillating? I also spot-checked several inputs to the chip according to the truth-table and the levels were wrong and on wrong pins, etc.

Any suggestions on troubleshooting this thing? I've never had to deal with a PLL before and not really sure where to start!

TIA and 73,

 

[doffo]

I have a few of those radios. One behaves like the one you have. I did start to recap the radio section by section, but still no luck. There is one part of the board I still need to recap, but I worked on the radio about 5+ years ago. Someday I will run into it again.

 

[nomadradio]

Not to put too fine a point on it, but did you verfy the PLL chip has power? Troubleshooting a dead radio should begin with an inventory of all the power supply branches and regulated voltages. A radio old enough to use zener diodes to regulate critical circuits especially. Dead zeners were a common failure back in the day when this was the common design choice.

73