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OT: MFJ-259B Fault


#1

Hello All,

Earlier on while pruning my 4m slimjim (it is now on song, more on this at a later date) I noticed my MFJ-259B was acting strangely.

On certain ranges, the unit is displaying nonsensical frequencies at the bottom end of the TUNE knob’s travel. On the 114-170 range the unit displays “0.0000 MHZ” until about 119MHz is reached. Tuning LF on the 27-70 range the unit gets to about 28MHz and suddenly displays 140.60MHz. You have to tune all the way back up to about 38MHz before the thing regains its senses.

I know a lot of people in SOTA use the same bit of kit, so before I go delving further,with precision capacitors and resistors and seeing if I can make any sense of it all, I thought I’d have an ask here and see if the tale is a familiar one. In this instance it would seem that Google in not my friend!

Any and all suggestions gratefully RX’d!

73,

Dave M0MYA.


#2

In reply to M0MYA:
Dave are you running on internal batteries or an external power source. Mine did similar things a few years ago - turned out to be batteries running low…

73 Graham G4FUJ


#3

In reply to G4FUJ:

Hi Graham,

Long time no QSO! Thanks for the suggestion. Indeed, it is something I have considered and have not yet tried to disprove. The startup V indication checks out OK, however I have noticed that my 259 always reads voltages (batt and external) lower than my DMM, which I find curious. It would have been my first recourse had I not left the “barrel connector to bit of wire” lead in Bangor. Sadly, I was there today to gather some experimental data for my honours project and did not think to pick it up.

I could hear a slight rattle inside and took the cover off it to investigate - as soon as I did this it started to play the game again.

I’ll explore this avenue ASAP, it sounds hopeful, asuming I can duplicate the fault conditions!

73,
Dave M0MYA

Edit: I forgot to log Geoff out again, sorry!


#4

In reply to M0MYA:
Try to push the tuning knob down and tune to see if this hapent again.
Mine have familiar problems and it seems to be the tuning variable capacitor.
When you use external power make some turns of the power cable on a ring ferite to have the correct results on your display.

73 de SV2KGA - DM1SV


#5

In reply to SV2KGA:

Try to push the tuning knob down and tune to see if this hapent again.
Mine have familiar problems and it seems to be the tuning variable
capacitor.

Yes, that seems to be where the problem lies. Push the knob in and it works, pull it out and it (sometimes) replicates the fault. Thanks for the suggestion.

73,
Dave M0MYA


#6

In reply to M0MYA:
Yes, long time since we’ve worked Dave - been keeping up with your Dad though!
Well done SV2KGA - another one of these 259s (locally owned) had the same fault which I’d forgoten about. I think the owner cleaned the capacitor Dave, will pass on his fix if I hear him.
73 Graham G4FUJ