[TenTec] 540/Triton Transmit Audio Distortion

[Bill ACITO, W1PA]

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