Good Morning Don / Andrew: I very much appreciate both your suggestions.
DON: I do have the KPA100UPKT installed and R4 is 100K. So, I will lift D8 and see what results I get. BUT first, I'll check the caps in the rectifier section as Andrew suggests to make sure all is well there. Now to call Mouser and get another MAX1406 on the way............ Thanks guys and I'll keep you up on how things work out. 72 Jerry N0JRN On 12/14/2009 6:22:37 AM, Don Wilhelm (d...@w3fpr.com) wrote: > Jerry, > > I will take back what I said about U4 - it is faulty. > That negative voltage is there only to allow the RS-232 drivers to > produce a negative level, the current draw should be minimal. > The only thing U4 does is convert RS-232 levels to TTL levels and > vice-versa. > > Actually -28 volts is a bit much and does exceed the maximum speced > voltage for the chip. -12 volts is more than sufficient and even -5 > volts is OK, so lowering the voltage a bit will help with the life of > the chip. > Do you have the KPA100UPKT installed (look for blue toroid cores at L16 > and RFC1)? If installed, change R4 to 100k if it is not already. > If R4 is already 100k or you have red toroid cores at L15 and L16, > remove D8 to drop the negative voltage to about half its present value. > > The KPA100 amplifier will function fine without U4 installed, but you > will not be able to use the RS-232 portion of the AUX I//O connector. > > 73, > Don W3FPR ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
