Connex 3300 HP frequency problem

[nomadradio]

I'd like very much for someone to explain what causes the 4008 chips in these radios to fail.

A 'scope on the divisor-input pins of the PLLchip will typically reveal 'bad' logic levels, hovering between logic high (8 Volts) and logic low, which should be under a Volt. Anything in between is a failure.

73

 

[Handy Andy]

I've always thought theses "fails" were from static and end user abuse - rapid rotation (channel change) and heavy modulation - the swing peaks can easily force a drop in voltage to feed these chips - even in a high-impedance state like driving a PLL chip. They do use diodes - so it may be they "rectify" and can force lines higher than supply rail during those "peak demand times" and a reverse bias moment and poof...shot or blown output