These are the output boards. I have completed
the right channel board here. Boards are defluxed
and washed. All new Capacitors, polished
connectors, and new "Thermalcoat" on
transistors. I have installed a Vishay multi-turn,
precisions trimmer (bias adjustment). If you have
never used a trimmer like this, you're missing the
boat. These are great and make adjustments very
precise. Each turn only changes resistance by a
small amount. The standard trimpots will change
as much as 10% with the smallest adjustment.
Bias on this is set to 50mv.
There is no DC offset adjustment on the 700M.
This is handled by two matched transistors
(2SA620WL). These have been out of production
for a long time. I found some equivalents, but I ran
across a company that still had originals in stock.
I found a complete set of original transistors for each
board, but only had to replace the two in the NFB
circuit, to bring the unit into good operational spec.
After a 15 minute warm up the right channel is now at
12.5mv (a long way from the original 870mv
reading!!!). The left channel is at -14mv (originally @
-50mv). The new values are excellent!!!
(0-10mv=excellent, 10- 20mv=good, 20-30mv=not
anything > 50mv=you still have a problem...)