Saturday, December 14, 2019

Icom IC-746 DC Filter Board Repairs

This post is about the repair of the DC power input filter board B5143D in an Icom IC-746. This is an uncommon failure in some of Icom's amateur and commercial gear of this era. The metal used in the plating of some parts will grow "dendrites" (metal whiskers) over time and cause arc-overs of some of the higher power portions of the PC boards. In this case, there was only a small distance between the high current DC positive voltage input terminal and the PCB ground trace of the power supply filter board B5143... one the metal whiskers got close enough to ground, and BOOM!! ... A short circuit appeared, and the high current capability of the power supply turned this edge of the board into an arc welder. 

Upon initial inspection it looked bad, but it wasn't too difficult to rebuild. These boards are no longer available, so replacement wasn't a simple option. I cleaned the board to determine how much of the board the fire had consumed, then used the scroll saw and cut that part of the board away. Since the damaged part was now carbon impregnated from the fire, it was conductive and had to be removed. 

Next, I cut a piece of perfboard, and bonded it to the original board with fiberglass resin. Another coat of resin was applied to the top and the bottom of the new part to better bond it to the OEM board. The new piece was then drilled and fitted with the power connector and the discrete components that were burned away. 

The repaired board was reinstalled, reconnected, and the radio was as good as new. Here's a few pics of the work...











C1 & C2 are the discrete capacitors that were blown away from the OEM board...




Finished and ready to go!

Dave WB4IUY
http://www.WB4IUY.net


Friday, November 15, 2019

MyHamShack.com, Check it out!


There's a cool, free service at www.MyHamShack.com . You can upload pics, meet people, post items for sale, blog, and more... and it's totally free. I've had a page over there since 2010, have made almost 400 ham radio friends, bought and sold some ham radio stuff, and enjoyed thousands of photos of other ham shacks. Check it out!


Dave WB4IUY
www.WB4IUY.net


Wednesday, November 13, 2019

JARSFest This Sunday 11/17/19!!

JARSFest This Sunday 11/17/19!!

Don't miss this great hamfest, 8am-1pm, tailgating, food, indoor spaces, lots of stuff!! Benson NC USA, at the Armory. More info online at: https://jars.net/jarsfest.html  

Tuesday, August 13, 2019

Ameco R5 Resto Update...

In 2017, I restored an Ameco R5K (kit version) shortwave receiver I received from my friend Joe KA9QAT. It worked pretty good, but while surfing the web I stumbled across a blurb with an update published by Ameco on Dec 13, 1967. It converts all I.F. amps to common emitter configuration, and boy does it make a difference!! Below is the R5K schematic, followed by a marked up version with the mods. I wanted to get this uploaded before I lost it forever :-)

The original R5K Restoration blog is on my site HERE...