MFJ-266 Analyzer help

[KD2GOE]

I have/had a working MFJ-266 I need the schematic or need to know what "D3" is on the RF board
it is a SOT-23 device with the markings "AH" mighty be a HV but I am 90% sure it is "AH"
the unit powers up and tunes I can here it on my radio but there is no SWR or impedance readings the device D3 was smoked I can only guess some one plugged it in to the radio and keyed off in to it "dam friends I am never lending out my testing gear" any way I think it is a 5.1v zener diode..

http://www.s-manuals.com/pdf/datasheet/m/m/mmbz5221b-mmbz5261b_semtech.pdf
I have removed D3 all the other zeners test good

 

[Robb]

If static electricty makes it into that thing; it takes out the diodes. I would call up MFJ and talk to a tech and get some replaccement diodes. This is a common failure point with antenna analyzers.

But if one used it as a freq counter - as some have ignorantly done with that much RF - it is hard to say just how much damage can be done. Not saying that is what happened; but have read all manner of abuse and misuse.

 

[KD2GOE]

If static electricty makes it into that thing; it takes out the diodes. I would call up MFJ and talk to a tech and get some replaccement diodes. This is a common failure point with antenna analyzers.

But if one used it as a freq counter - as some have ignorantly done with that much RF - it is hard to say just how much damage can be done. Not saying that is what happened; but have read all manner of abuse and misuse.

Thanks rob I am going to call them up
I am going to hope with RF getting in to it will be ok and it just popped the 1 diod. ill call them up and make Shure I order the right part and pop it in and hope...

 

[Robb]

I've alsso heard many say that it is best to ground the conductors of your antenna coax/ladder line before you attach it to the analyzer, in order to keep excessive static from damaging the analyzer. Makes sense.

 

[KD2GOE]

well looking deeper in to it... they look to be Schottky diode not Zener... I though it was odd that the code on the part came back 5.1v zener when it is in an RF circuit.... so I whent and ordered the Schottky diode 's and 20 IRF520's to have on hand

I called MFJ guy there told me to call back Monday

I found this info on the MFJ-269
http://802.11junk.com/jeffl/MFJ-269-repair/

 

[KD2GOE]

well it looks like MFJ cant help me. they cant even give me a schematic. I know 2 diodes D1 and D3 and R1 where cooked I replaced R1 I got the SWR reading back.
I used the info from http://802.11junk.com/jeffl/MFJ-269-repair/ to give me a guess at what there diodes where so I ordered 6 and was going to swop out D1, D2, D3, D4
at first I just did the 2 that where shot... ok seemed to help I did D4 and lost the SWR readings put the old one back and got the SWR meter back... so there leaves me to guess the diodes are not right at all...

I can't believe MFJ cant give me any info on a product they still sell!

ill have to Call them up Monday and press them some more.. I am trying not to get pissed at them...

 

[KD2GOE]

I have to do some more testing but I think I have it working 90% +
I tested some old schottky diode I snagged out of old radios..