I picked up a Yaesu speaker-mic at a hamfest. It came with a broken Yaesu / Vertex VX-150 HT.
Radio problem: squelch is stuck open.
Stuck open to the degree that even tone squelch didn't make any difference.
CPU reset did not help.
I examined the schematic found online and noted the squelch and lamp buttons are shared on the same CPU pin, selected by differing resistance to ground. Coincidentally, the lamp on the unit was stuck on, too. Hmmm.
I disassembled the unit and found under 10x magnification that pin 3 on the CPU physically was not attached to the trace below -- I could push it down with a pick. A bit of flux and fine solder to reflow the pin resulted in a completely working unit.
If I interpreted the circuit correctly, this line is tied high via a resistor. Also connected are the buttons via two resistors of varying value. When a button is pressed the voltage varies on the pin. When the pin is not connected or floating -- it's indeterminate. Not logic high, probably low? As such the radio interprets the pin as having both buttons -- light and squelch -- held down permanently.
Pin in question
Disassembly -- remove knobs, remove rubber gaskets around knobs. Unscrew antenna, leave SMA connector in chassis untouched. Pull charge / mic plugs loose from jacks but leave rubber flaps on chassis. Remove belt clip, remove battery, remove sticker under battery. Remove two large flat silver screws under the sticker. Note a "personality board" that is likely stuck to the sticker. Leave two black philips screws in upper battery compartment alone. Case should now separate from the bottom like a clamshell. Note battery snap will fall loose in this process, remember to replace later. Also, note that the flat board that probably came out with the sticker inside needs to be replaced for the radio to turn on during testing.
This page last modified Mon Apr 12 08:24:04 CDT 2021 by timc!