[TowerTalk] Servicing an MFJ 259B

[Joe Subich, W4TV]

On 2014-08-30 9:35 AM, Herbert Schoenbohm wrote:
> I even gave the solution provided to me by Joe W4TV of changing the
> value of the voltage divider resistors to cause the pass transistor
> to shut off completely when not selected.

The changed resistor values in the RCS-12 source drivers are a patch.
The issue is a basic design defect - the "pull up" resistor is on the
"wrong side" of the base current limiting resistors which mans the PNP
pass transistor is not cut off when not selected.  The defect can be
seen when comparing the RCS-12 schematic with that of the W9XT HSD-9
"high side driver" board.

While this is not a service issue, it is indicative of the overall
lack of attention to detail/quality control in the MFJ family in
general.

73,

    ... Joe, W4TV