Need digital side schematic for MFJ-247 Antenna Analyser

Discussion in 'Radio Circuits, Repair & Performance' started by KC1JTS, May 3, 2019.

ad: L-HROutlet
ad: l-rl
ad: MessiPaoloni-1
ad: K5AB-Elect-1
ad: Left-3
ad: Left-2
ad: L-MFJ
ad: Subscribe
  1. KC1JTS

    KC1JTS Ham Member QRZ Page

    I picked up an MFJ-247 analyser at a swap meet semi-working. I believe the issue is low signal to the digital counter circuits, as the frequency is not stable and the upper freqs read as zero even when the analog meter is working. I have the first 2 pages of the schematic, but not the page that shows the digital counter and display circuits. MFJ doesn't have them in hand either. Does anyone have these, or can you tell me if another model of the mfj used the same circuits?

    Thanks,
    Bill KC1JTS
     
  2. KP4SX

    KP4SX XML Subscriber QRZ Page

    I have a 259 which may have the same arrangement. The counter module itself was not made by MFJ and is unobtainium nowadays. The 259 schematic doesn't show any details of the counter either.
    I used a cheapo $8 chinese counter module to replace mine and it fits and it works! Easier to read too! Downside is that this particular module only goes up to about 70 MHz which happens to suit me fine.

    mfjsqualo.jpg
     
  3. KC1JTS

    KC1JTS Ham Member QRZ Page

    Thanks so much for the reply. I was really just looking for the connection information. I believe the 249 and the 247 use the same or similar digital boards, and I was able to find the connection page schematic for that model. Looks like a pretty simple setup. As part of my diagnostics, I set the MFJ247 to 'frequency' mode ("B" input on the display), and then crossed the output of the antenna jack to the freq counter input. When I do this the freq reads just fine, so I assume the issue is the buffer circuits going to the "A" input side. I'm assuming the driver transistor or it's biasing transistor are at fault, and will try replacing them from the digital board input back out towards the oscillator. Sure wish I had my old Tektronics 50mhz scope back. (Sigh)
     
  4. KP4SX

    KP4SX XML Subscriber QRZ Page

    Are you familiar with the instructions for setting the pot R32 (in the 249/259) on the counter module described as "BIAS"?
    I bought my 259 as a junker that apparently had been left outdoors for along time and the LCD counter module was toast so I have no experience with it.
     
  5. KC1JTS

    KC1JTS Ham Member QRZ Page

    No, I am not familiar with that procedure. Do you have the instructions for setting the bias?
     
  6. KP4SX

    KP4SX XML Subscriber QRZ Page

    Sorry for the disappearing act. I wasn't following the thread. Let me scan those pages so that everything remains in context. I'll post them tmw.
     
  7. KP4SX

    KP4SX XML Subscriber QRZ Page

    IMG_20190514_0001.jpg IMG_20190514_0002.jpg

    I don't know the source of this particular document. Seems like something in-house from MFJ.
     

Share This Page