[ICOM] 751A Main RF Board

[EP Swynar]

Hi Guys,

Here's a good one...

A year ago, my venerable back-up rig --- the Icom 751A --- suddenly went belly-up in the transmitting department. A tekky friend of mine, who is in the business of consumer electronics repairs, had a good long look at it, & determined that a 9-MHz crystal-controlled stage on the main RF circuit board wouldn't oscillate in transmit...no idea why, either (all the parts, voltages, etc. therein apparently checked A-OK).

Anyway, last summer I bought a complete 751A board (less filters) from a fellow who was parting-out his rig. Great! I'll just swap out the "bad" board, & replace it with the new one...

Well, to-day I proceeded to carefully dismantle my board from the rig, recording which connector goes where, etc. etc. etc. ... and all went well, too, until the end, when I finished-up with a black wire that pulls out of a post at the juncture of diodes D-161 & D162 in my 751A...

The problem is, there is no such post on the board that I purchased...and no diodes D161 or D162, either.

I examined my 751A service manual schematics, circuit board outlines, and parts list --- and learned, to my complete & utter dismay, that these diodes aren't listed in the manual, either!!!

I must have a newer-vintage transceiver which was manufactured AFTER the manual was printed, or an older transceiver & a new manual --- with a brief history of any & all engineering revisions made to the rig being NOT duly noted therein...(sigh!).

The black wire goes from the afforementioned post, and plugs into the Matrix board.

I am debating whether, or not, I should simply proceed with the swap & tape the wire off to one side (the same way automobile manufacturers do with redundant underhood wires in the face of upgrades) & hope for the best, or do as my friend did last summer, & simply part this sucker out to the world, piece by miserable piece...

~73!~ Eddy VE3CUI - VE3XZ

PS: How come I never have this problem fixing-up my old Drake & Hallicrafters rigs...?!