amateur radio operators MFJ-266 antenna analyzer

[mkube396]

I am trying every thing to fix this analyzer I have contacted the people at MFJ and they cant help me and 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 the diodes on the RF board are SOT-23 device with the markings "AH"
I found some info on a MFJ-269 Repair I found "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... did not do much 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...

So if any one has an MFJ-266 antenna analyzer can you look inside on the RF board next to the N-connector and tell me what value of Resister "R1" is or the print in it i think it is a 50 Ohm and if they can identify what D1, D2, D3, D4 are .. I can't believe MFJ cant give me any info on a product they still sell! 

[mkube396]

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 an old radio..

[German_EE]

Try posting your question in the Repairs section of Eham.net. There are a few hams here but not many of us may own an MFJ 266.

[David Hess]

I am trying every thing to fix this analyzer I have contacted the people at MFJ and they cant help me and cant even give me a schematic.

If they do not do their own design and development, then they may not even have one.  Their lack of support is the major reason I have avoided their products.

It is especially annoying with an instrument like the MFJ-266 where most of the failures will be repairable.

[Fraser]

It is always worth asking yourself what likely happened to the unit in order to kill it. Connection to the RF output of a transceiver would be a possibility. From the failure scenario you can often assess which components likely took a hit and died. I own MFJ259's so regret I cannot be of much help. The schematics that I got for my 259 from MFJ were hand drawn by one of their techs and not a professional schematic diagram.

I often have to work without  a schematic and after assessing the 'patient' and the likely cause of the fault, I draw the schematic for that area of the PCB (or sometimes all of it!) Repair is so much easier with a schematic and such is always good to have in case of need in the future or modifications. It is worth the effort.

Good luck with the repair

[Andy Watson]

Appears to be a re-badged Feature Tech AW07A.

[Fraser]

Excellent spot Andy !

AW07A internal pictures here:

http://www.radioscanner.ru/forum/topic43564.html

https://translate.google.co.uk/translate?sl=ru&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.radioscanner.ru%2Fforum%2Ftopic43564.html&edit-text=

Picture attached.

Useful pictures of SWR analyser input-output here:

https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=ru&tl=en&u=http://www.rigexpert.com/index%3Fs%3Darticles%26f%3Daas%26l%3Dru&usg=ALkJrhjgtlj00dFP9MXQDz9gzppDVf64mw

https://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.co.uk&sl=ru&tl=en&u=http://www.rigexpert.com/index%3Fs%3Daa520%26f%3Dinside%26l%3Dru&usg=ALkJrhhs257ULbBi-N51auDn7RUpOmzweQ


AW07A is made by BA5RW. It may be worth contacting him and asking for a partial schematic for the area of interest.

BA5RW Blog is here:

http://ba5rw.blog.sohu.com/

Email address is:  ba5rw@hotmail.com

Personal data:

https://translate.google.co.uk/translate?hl=en&sl=zh-CN&tl=en&u=http%3A%2F%2Fba5rw.blog.sohu.com%2F

[mkube396]

ok thanks guys you have been a ton more help them any other forum

[GreyWoolfe]

It is always worth asking yourself what likely happened to the unit in order to kill it. Connection to the RF output of a transceiver would be a possibility. From the failure scenario you can often assess which components likely took a hit and died. I own MFJ259's so regret I cannot be of much help. The schematics that I got for my 259 from MFJ were hand drawn by one of their techs and not a professional schematic diagram.

I often have to work without  a schematic and after assessing the 'patient' and the likely cause of the fault, I draw the schematic for that area of the PCB (or sometimes all of it!) Repair is so much easier with a schematic and such is always good to have in case of need in the future or modifications. It is worth the effort.

Good luck with the repair

Could you post the schematic for the 259?  I have one that I got from a ham radio "yard sale" that works fine, but the schematic would be nice to have.  Mine is the straight 259, no letters.

[kc9qvl]

Mfj-259b  Mostly the same as 259

[albert22]

Here
http://www.w8ji.com/mfj-259b_calibration.htm
 is plenty of info on the 259BR. probably uses the same resistive bridge as the 266 and the same diodes (HSMS2820).
If R1 is part of the "legs" of the bridge then it should be 50 ohms. If not, it could probably have a symmetrical on the other side of the bridge.

[GreyWoolfe]

Mfj-259b  Mostly the same as 259

Many thanks, Kemosabe!

[KD0CAC John]

I have a few different antenna analyzers MFJ-259 & B , MFJ-269 , Timewave TZ-900 and miniVNA Pro .
I've repaired a few of the MFJ's , watched the AW07A show up and MFJ bought the rights to it and raised the price $100-150 , this is a BS markup and MFJ seems to be monopolizing , or attempting to the ham radio market .
Up until this , I thought MFJ provided marginal products at a non-highend price .
If you consider them to be an occasional partial kit , then it may not be too bad
As far as MFJ's diagrams , they just plain suck , when chasing some down I came across Tom's W8JI's post on a ham radio forum , as I remember , he made a comment about doing some consulting in the 259 , 269 and mentioned not to use the calibration info from MFJ , he has a page that is referred to here on cal. & diagram that seems to come from Russia - the diagram ?
Looking at your picture & comment about diodes near the RF connector , just a SWAG , they may be detector diodes , that can be damaged by RF from transmitter , as mentioned earlier , and also from static - I know keep connected 50 ohm dummy loads to all my analyzers , I am also suspecting that the RF can be a number of sources like local broadcast stations , common mode current .
Grounding RF feedline before connecting to gear is good practice , and maybe build a meter to check for CM , stray currents etc.
Again , hoping your picture of adding wired components on to the board is just a test , I can not imagine that you would get useable readings with that type of repair ?   

[Fraser]

For those wanting the hand drawn MFJ259 (NOT 'B') schematic, I attach it here.

MFJ259 calibration manual added and this includes useful info as well.

Aurora

[mkube396]

sorry for my late post 

Well i fixed it i was unable to fined the right diodes for some reason  i ended up sticking in some old detector schottky diodes from an old CB radio and it works fine now! i tested it with a few resister values to simulate different SWR readings and every thing was dead on.

may i ask how did it break?

static discharge... it killed the schottky  detector diodes...

[Richard Head]

A BAT54 (SOT-23) would probably be suitable.