Resolved.
After finally doing some real voltage checks per the manual rather than just
the board swaps, I found the +8 (REG) line at 13.8V. I ordered and replaced the
MC1723CL on the source logic board. Popped the board back in, and sure enough
---13.8V. What the heck?
Opened the schematic in my original manual, traced it around, and noticed the
octal plug. Checked the wiring versus the manual, 2 to 4, 6, 7, and 8 together
etc. Looks ok. Back to the schematic... 2 to 5 and.... huh?
The original 540 manual text is wrong (page 2-4)... says short pin 2 to 4.
Schematic is correct: 2-5. Previous owner had read the manual when they built
the plug, not the schematic. 2-4 shorts and backfeeds the 13.8 line to the +8
regulated line (which is used on the SSB board... no wonder my audio was “hot”
and distorted). He must have been a CW-only guy.
Corrected the octal plug, full re-alignment, rig works and sounds great. Got
several good audio reports on 20m this weekend.
I Googled this manual issue and found nothing; I can’t believe I am the first
one to find this. The pdf version that is floating around the web is correct.
The original hardcopy that I have is wrong. Anyone else heard of this?
I found an original resistor on the logic board that was also way off versus
the schematic – 180 vs 4.7 ohm in the schematic.
Bill W1PA
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