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February 24, 2012, 12:08:51 amThanks to Eugene52 now I have the schematic I can look at some mods maybe a micro to drive the TX coil and vary the frequency. Some analogue inputs to monitor parts of the circuit. As a tip the 1 meg resistors may go higher value over time due to ageing. The higher the value of a resistor the more likely to ageing on a 30 yr old circuit. As they are used in setting the gain of the amplifiers the gain will increase with ageing and may become unstable. R53 carries a high current to switch the TX coil so this may have also gone high with a lot of use. Hope this helps. Last modified by: echoshack February 24, 2012, 12:10:17 am