Here is the complete calibration procedure for the 259B. A quick scan
through didn't show a way to change the oscillator, just check it.

http://www.w8ji.com/mfj-259b_calibration.htm

Dick - W6CCD

On Mon, 19 Jul 2004 02:04:12 GMT, Gary Danaher
wrote:

It seems to read about 250 hz high. As you say, perhaps close enough for
government work, but I needed it the other day. A new ham came by with
one of the RS 10 meter rigs he bought last year on sale. From my
Kenwood, he was about 250 low and sounded just horrible, but the only
counter I had at home was the 259B and it showed it was real close, so
later I tried it on some 2 meter fm radios and it ran consistently high.
I used to have an original 259 that died and I recall the counter
circuit was on the back of the display and was adjustable. Even GOOD
counters can be adjusted, so there should be something here as well, but
I hate to take it all apart without a clue where to look.

Fred McKenzie wrote:
Is there an adjustment pot on the MFJ259b for the freqency counter and
if so, what number is it on the board?

Gary-

It looks like the counter module is purchased as a unit, probably from
Optoelectronics. Therefore, MFJ may not know anything about it they don't need
to know.

I've looked for anything that might calibrate the frequency, but couldn't find
it. Perhaps further disassembly would have revealed a hidden trimmer
capacitor. I doubt it would be a pot, but you never know.

How far off is yours? Mine is close enough for its purpose of checking
antennas, but I wouldn't adjust a transmitter's frequency with it.

73, Fred, K4DII