Fixing a fake ADF4351 synth board

A couple of months ago, I bought some ADF4351 synthesizer boards at a very attractive price from a Chinese supplier.  Sadly, the supplied boards turned out to have fake, or out of spec, 4351 chips which actually behaved like 4350s, with no /32 or /64 divisor.  As a result, it was impossible to use them below about 130MHz.  Several UK microwavers including RadCom columnist Andy Talbot G4JNT were also supplied with these fakes

Following up Andy’s suggestion in his Design Notes column in the Nov 2016 RadCom , I decided to swap one of the fake devices for a new  ADF4351BCPZ bought from RS (stock no 796-8710, £9) and can confirm that the board now behaves correctly at /32 and /64.  It just needed a bit of concentration, a fine soldering iron, lots of flux and a stereo microscope, then a 100W iron to flow the solder into the heat transfer pad from the underside.

I removed the fake chip by applying the 100W iron to the underside of the board beneath the chip, then used a hot-air blower to melt the solder on the top side of the board, lifting the chip away with tweezers.  Next, I applied a good dose of liquid flux, then cleaned off the pads with desolder wick.  I applied a bit of solder to one of the pads, then more flux, positioned the new chip, melted the solder to attach the device with the chip firmly held down, then did the same at the opposite side, but followed the technique recommended by Andy and others, using a flood of flux and a fair excess of solder.

I ran the iron across all of the pins and pads on each edge of the chip, then removed the excess using desolder wick, ensuring I cleared all bridges. Surface tension did the hard work, although I did have to reflow two of the pins after close examination under the microscope.

The repaired board is in the picture. The chip is 5mm square. Notice that the markings appear very sharp and the pin-1 dot is very distinct,.

Replacement ADF4351 ship mounted on a green PCB

Now compare one of the fake originals. The soldering is much better of course, but the label is indistinct and the dot is almost absent, as though the top surface of the chip was abraded and then printed with a new identifier. The lettering does look 100% the same.

Fake ADF4351 before replacement- actually a re-marked ADF4350

3 thoughts on “Fixing a fake ADF4351 synth board”

  1. Hello Mr. Smithn

    Recently, i have planned to make a RF generator with ADF4350 but i faced the same problem to you. I bought 2 boards ADF4350 and ADF4351 from aliexpress (links: and about 2 months ago and used Arduino Uno R3 to control them via SPI interface in Arduino. Here is libraries i have try: ;; . The result is that both of these boards generate nothing (measured by a 500 MHz oscilloscope, no waves, no frequencies, PLL Led on board also isn’t lighted). I hope i can hear your advice to solve this problems soon.


  2. Hello Mr. Smithn

    I just want to clarify is on the picture really repaired board or this photo was made before the repairing?

    I have bought ADF4351BCPZ chips on Aliexpress with absolutely the same marking (literally the same, each symbol) as on your photo, and they behaves as ADF4350 – devisors /32 and /64 do not work.


    1. Yes the image is of the new chip I soldered to the board after removing the old one. I’ve added a second picture to the page now, showing one of the original boards which I haven’t modified yet. The chip markings are 100% identical apart from the fake one lacking the pin-1 dot and having very indistinct markings. Hope that helps.
      Neil G4DBN

Leave a Reply

Your email address will not be published.