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Next Issue The March 2016 issue of SILICON CHIP is due on sale in newsagents by Monday 29th February. Expect postal delivery of subscription copies in Australia between February 29th and March 5th. Serviceman’s Log . . . continued from page 43 going around in circles for an hour, I decided to replace all the electrolytic capacitors since these devices are notoriously unreliable once they have aged. There weren’t many so it was a cost-effective way to hopefully make some progress. Replacing these capacitors actually seemed to make a bit of a difference, so I packed up and returned to the glasshouse. However, I wasn’t convinced that I’d found the fault, so I took the precaution of taking the signal tracer, an oscilloscope and a floodlight along with me, just in case. After reconnecting the module and turning on the power, I was dismayed to discover that nothing had changed! I listened in with my signal tracer and again there was lots of noise but it was now quite loud – much louder than at my workshop. It seemed to be everywhere, even on the supply rails, and then I had a light-bulb moment! The nearer I got to the battery with the signal tracer, the louder the noise became. I put the tracer aside, grabbed my digital voltmeter and checked the battery voltage once again. This time though, I held the meter there long enough to see that the battery voltage, now sitting at 46V, was fluctuating minutely. I then went from cell to cell with the voltmeter and each one read a nominal 2V until I got to about cell number 20 (yes, I had started at the wrong end). This cell had a reverse voltage on it and it was fluctuating wildly. In fact, it was producing enough noise to break through the filtered supply rails and regulators of the control module and create havoc. Since the cell was effectively dead, I bypassed it with a jumper cable and everything sprang to life. The solenoids worked as they should and the rear wheels accelerated smoothly. When I looked inside the faulty cell, I could see that the plates were quite distorted and almost corroded away. I made up a more permanent link to bypass the dead cell and advised the “Duck’s” driver that doing so would put more load on the other cells and that they would probably have to have the lot replaced one day soon. My guess is that it would cost at least $2000 for a new bank of batteries so I was happy that I had at least given them time to consider whether to spend that money on a new heart or to retire “The Duck” when it eventually broke down again. I also told the maintenance man not to leave the charger on for extended periods and to carefully monitor the state of charge. And the clue I had missed right at the beginning? Having unplugged the charger when I first looked at “The Duck”, the freshly-charged battery should have measured at least 50V and probably as much as 56V; certainly not 48V. The dead cell was not only not contributing its normal 2V but because it was negatively charged, it was subtracting that amount from the overall voltage. Advertising Index Altronics.................................. 66-69 Core Electronics........................... 57 Digi-Key Electronics....................... 3 DSCAPE...................................... 95 Hare & Forbes.......................... OBC High Profile Communications....... 95 Icom Australia................................ 5 Jaycar .............................. IFC,45-52 Keith Rippon ................................ 95 LD Electronics.............................. 95 LEDsales...................................... 95 Master Instruments...................... 13 Microchip Technology................. IBC Ocean Controls............................ 11 Rohde & Schwarz.......................... 9 Sesame Electronics..................... 95 Silicon Chip Binders..................... 37 Silicon Chip Online Shop........ 88-89 Silicon Chip Subscriptions........... 53 Silicon Chip Wallchart.................. 87 Silvertone Electronics.................. 65 Tendzone........................................ 7 Tronixlabs.................................. 8,95 There is a well known adage in the industry that I had failed to apply – always thoroughly check the power supply before anything else! A bad power supply can be the root of so SC many problems. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. 96  Silicon Chip siliconchip.com.au