[sdiy] 4051 spikes

[rsdio at audiobanshee.com]

Thanks for that analysis, MC.

I've seen products as recent as a decade ago suffering from CMOS latch-up when the input voltages exceed the supply. Amazing how so many designers don't understand the limits.

Brian


On Apr 27, 2015, at 6:34 PM, Michael E Caloroso <mec.forumreader at gmail.com> wrote:
> When I started restoring my OBX I was determined to uncover why so
> many of these show up broken.
> 
> Turned out that these things eat 4051s because the Vdd 5.6v rail
> circuit is a poor design.  It was derived from the 15v rail using a
> diode/resistor drop, which isn't a regulator at all.  It will vary
> with load current.  When the CMOS ICs are in transition they are
> drawing more current which pulls down the 5.6v rail, zapping the 4051s
> over time until Poof!
> 
> The OBSX and OBXa have that design error too.
> 
> It didn't help that they used first generation RCA CMOS with ZERO
> overvoltage input protection.
> 
> MC
>