A few days ago I posted a request for help with loss of sensitivity on my K3's main and sub-receiver. The problem was quickly identified by Van, W1WCG as a known issue - failure of PIN diode D5 on the KXV3 board. D5 is a pinhead-size 3-terminal surface mount device (actually two diodes in one package) that routes signals to the main and sub-receivers during receive. Failure of the diode is caused by electrostatic discharge (from thunderstorms) or a strong RF field from a nearby transmitter (which was the cause of my failure.)
It is possible to replace D5 either by sending the KXV5 board back to Elecraft, or simply by replacing the diode in one's workshop, which is what I did. The Elecraft part number is E560047. Replacement diodes are also available from Digikey (p/n 568-1932-1-ND) and Mouser p/n (771-BAP64-04W-T/R), and the manufacturer's part number is BAP64-04W. The cost is only $0.54 in small quantities, and it is advisable to buy a few spares. The PIN diodes in this device are rated at 100V reverse breakdown. Since failures of these diodes are a known problem, it is better to replace them with a more robust substitute. Fortunately diodes having identical electrical specifications are available at the same price, but with a 175V breakdown rating. For these, the part numbers are Digikey: p/n 568-1931-1-ND, Mouser: p/n 771-BAP64-04-T/R, Manufacturer: p/n BAP64-04. There is a small problem with ugrading D5 to the higher voltage version: the package sizes are slightly different. The 100V diode has package SOT323, whereas the 175V diode has package SOT23, which has marginally wider pin spacing. Fortunately, there is enough overlap between the pins of the larger device and the solder pads on the KXV3 PCB to ensure a reliable solder contact. However the magin of error for alignment is reduced, and so if you want to substitute the more robust diode, you must use particular care in making the substitution. Replacing SMT devices requires a steady hand and good eyesight. Although, replacing D5 is not difficult, I don't recommend it unless you are comfortable working with SMT components. I also recommend that Elecraft specify the larger PIN diode in any future revision of the KXV3 board in order to increase reliability. 73, Jim Garland W8ZR ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
