The value of D9, assuming it was a glass Zener diode, is a bit of a problem. Based on the clamping voltage of the MOV (82V), and the maximum working voltage of C1 (25V), R2 must have at least 30 mA through it for C1 to be protected at clamp time. That would mean that R5 would be dropping 12 V, leaving another 12 V at D9's cathode. D9 would have to be conducting by then, else C1 would be over-voltaged. So it's at most a 12 V Zener, and can't be a glass Diac (which has a breakover voltage higher than that).
If D9 was a forward-biased signal diode R3 must have approximately 0.5 mA through it before Q3 can start conducting, that would pin D9's _anode_ voltage (the cathode in the schematic) at around 1 V when regulation began. R4/R1's current would be approximately 0.7 mA, so R5's current would be 1.2 mA. That would make the voltage on C1 approximately 1.5 V, which seems too low. From this I conclude that D9 _is_ a Zener diode, of less than 12 V in value. Zener diodes start at around 1.8 V in value, but I think I'll first try something like a 6 V rating. The 1N6309-20 diodes are glass, at 2.4-6.8 V in rating. 1N6319 is a 6.2 V glass Zener. 1N746A-59A are glass, at 3.3-12 V in rating. 1N753A is also a 6.2 V glass Zener. There are plenty of candidates to try. -- Jim _______________________________________ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
