[CQ-Contest] Mods to MFJ-432 Voice Keyer?

[k8cc]

At 08:00 PM 11/2/00 -0800, Dennis Vernacchia wrote:
>We offered to fix it ourselves if MFJ supplied us a schematic.  THEY WOULD 
>NOT, even after we suggested we sign a non-disclosure for any propietary 
>information.

Funny - my MFJ-432 (purchased in March 1997) had a schematic in the 
manual.  I'll see if I can find it - if its not marked proprietary maybe 
I'll scan it and put it on the web for other's benefits.

Its stupid for a manufacturer to refuse documentation for something as 
simple as the MFJ-432.  Most of the design is an adaption of the data sheet 
for the main IC.  Anyone wishing to clone the unit could trace out the 
circuit on the PC board in short order.

One thing I did not like about the MFJ-432 is that the +5V bias for the 
internal electret mic also appears on the external mic as well.  While I am 
not certain that this will hurt a Heil headset, its not good design 
practice so I cut out the resistor the bias is applied through.  The 
internal mic no longer works, but since this has no use for my intended 
purpose, its loss was irrelevent.

On the other hand, the way MFJ uses DIP jumpers to configure the unit for 
ICOM, KENWOOD, or YAESU is pretty clever.  I've made good use of this 
feature, using the '432 with many different rigs.


Dave/K8CC


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