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| 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 adjustmnet 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 accross a company that still had origianls in stock. |
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| 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 warmup 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!!! (0-15mv=excellent, 15-30mv=good, 30-50mv=marginal, > 50mv=you still have a problem...) |
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