Topband: Additional MFJ-259B

Tod -ID tod at
Wed Apr 22 15:10:23 PDT 2009

I have continued to work on the repair of my MFJ-259B and think I have found
a way to determine by a set of simple measurements whether or not the diodes
are blown as opposed to the unit simply being out of calibration. There are
several Test Points on the PC board that can easily be reached by simply
removing the back of the case. 

I would like to have folks who are interested -- who have either known good
or known bad units [or maybe unknown status units] ---  make some
measurements and send them to me. The URL below tells how to make the
measurements and provides a table form for the data collected. Once you fill
in the table all you do is click on a button and they will be sent to me for

If you wish to participate in the data collection exercise go to this URL => It will show the location of the Test Points and how to
open the unit to reach them.

In addition, I made some estimates from the schematic of what the voltage
values of the Test Points should be for a good unit. [remember, this is not
'for sure' stuff, just best current estimates]. Also, there is a link to the
cleaned up schematic.

If you want a copy of the schematic or want to see my best estimate of what
the Test Point voltages should be go to this URL: =>

Tod, K0TO

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