[MRCA] Watkins Johnson blues, pt 2

[Ray Fantini]

Ok, results of the Watkins Johnson reference issues. Short review, looking at the attached drawing reveals that signal disappears at point B after the receiver gets hot along with both devices U-18 and U-19 having been changed. Did look with a meter, also installed jumpers across traces but that did not resolve the problem. Finally decided to remove all the jumpers and the socket for U-19, clean the board top and bottom with alcohol to remove dirt and flux and discovered almost every thru contact on the board was damaged. So, after installing a new socket and doing repairs that included a couple new jumpers to connect bad traces its been working so far.  But being a WJ product noticed that one of the other divide by five counters is intermediately flipping between divide by five and divide by four. That's on a socket too so going to assume that I will have to pull that, clean and do the same thing.
Figure that the dirt, flux or whatever on the pins that control the reset, clear and preloads for the counters that normally float high may be being pulled low after the crap on the board warms up? Had cleaned the flux off the bottom of the card but it appears the only way to do it right is to disassembled, clean and do a clean installation. They don't tie unused pins to anything so maybe that's a week point in the design.
You can't leave dirt and flux all around where you work without it generating issues, always a problem when you have to go back and redo someone else's work.

Ray F/KA3EKH








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