Re: Need help with 1980 Honda CB750K charging system

Posted by sgtslag on Jun 10, 2014; 12:18pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Need-help-with-1980-Honda-CB750K-charging-system-tp4051753p4051815.html

An AGM is an excellent, and expensive battery.  Running them dead in the bike is not good.  Take it out, charge it fully, then take it to any auto parts store for a free load test -- do NOT throw parts at your bike hoping it will get better!

If you have the cash, spend it by taking your bike to a qualified mechanic, and get it running so you can ride it.  Do yourself a favor and order this book:  Motorcycle Electrical Systems: Troubleshooting and Repair (Motorbooks Workshop).  The author is very good at explaining electrical systems, how they work, what tools you need and some you can make yourself, as well as how to troubleshoot electrical systems on old, and new bikes alike.

Luke is almost correct on how to use a DVM.  However, using the lowest resistance setting (Ohms), may, or may not, give you a valid reading.  Diodes have what is called a "break-over voltage" -- after you reach this voltage, they will conduct, but not until you apply the minimum voltage.  For Silicon Diodes, the break-over voltage is 0.6 Volts, at which point they turn on and conduct, in one direction, or polarity.  Only if your DVM's resistance mode applies 0.6 Volts, or higher, in the proper polarity, will it give a reading other than infinity.  The Diode Test mode applies 0.3-0.6 Volts (Germanium Diodes conduct at 0.3 Volts), to check for conduction, to see if the diode is working properly.  Cheers!