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links are not installed) but it functions as a half-wave voltage doubler when the links are installed for 110VAC operation. I also noticed that there appeared to be a thermistor wired in series which had burned out. There were also two optoisolators on the board. One seemed to be used to indicate to the control circuit when the AC input was present. I think this signal may be important when power is first applied but I did not trace the circuit further to find out. For 110VAC input, the optoisolator was connected via a 27kW resistor to the incoming AC line. For 240VAC input, there was an extra 27kW resistor in series. When the wire link is installed it shorts out the second 27kW resistor. But for cost-saving reasons, the manufacturer did not install the second resistor when factory configured for 110VAC input. This made me question whether the optoisolator may have been blown when 230VAC was applied. I thought at this point I might as well make the changes required for the unit to operate from 230VAC, plug it in and see if it worked. I didn’t have much to lose; if anything else had failed, it would probably just blow the fuse when powered up. I didn’t have a replacement thermistor but even though a chunk had blown out the side, the resistance across its pins didn’t seem too high at 32W. This was probably higher than a good thermistor but still low enough to allow the power supply to operate with a light load. At least I would know if it still worked. So I made the changes and replaced the fuse. I didn’t have the correct slowblow type of fuse on hand so I decided to use a regular fuse for testing purposes. I hoped that the inrush current at startup would not blow it. Sometimes, you have to try your luck! I put the PCB back into the chassis and sat it on top of a cardboard box to ensure that it was insulated from the top of the workbench. I connected the mains power cord via an earth leakage circuit breaker and switched it on at the power circuit. The fuse did not blow but there was a loud crack as a spark shot out of the side of the thermistor. Without touching the power supply, I carefully connected my Fluke multimeter across each of the DC output connectors. The voltages measured +5.1V DC, +11.95V DC and -11.96V DC. Whoopee! All was OK; I guess one can be lucky sometimes. But I still needed to replace the thermistor and put in a proper slow-blow fuse. On Saturday morning I made a trip to the local electronics store and fitted the new parts that afternoon. The power supply passed a no-load voltage test. Luck was on my side. The fuse had blown before any damage was done other than to the fuse and thermistor. The power Mosfet was clearly OK and the optoisolator had not blown up with only one 27kW resistor in circuit. I made a phone call to my friend to tell him that it was ready to be picked up. We decided to have a BBQ on Sunday and he would collect the power supply at the same time. I did not hear from him whether the power supply worked OK when installed into whatever it came from. I suppose if it had not worked, he would have let me know straight away. Sometimes no news is good news! SC New Rohde & Schwarz oscilloscopes Rohde & Schwarz have recently introduced the two-channel RTC1000 series, a compact, lowcost, high-quality digital storage oscilloscope. It can double as an eight-channel logic analyser, four-channel pattern generator and a protocol analyser for I2C, SPI, UART/RS-232, CAN and LIN; and as a digital voltmeter, component tester, spectrum analyser and counter. With this eightin-one instrument integration, users get more value with a minimal footprint on bench space. For further information contact: Rohde & Schwarz Ph: (02) 8874 5100 Email: sales.australia<at>rohde-schwarz.com Website: www.rohde-schwarz.com/RTC1000 siliconchip.com.au R&S RTC1000 oscilloscopes are available with bandwidths from 50MHz to 300MHz. Bandwidth upgrades are available via software license all the way to 300MHz and can be purchased as needed. The maximum sample rate is 2 GSample/s and memory depth is 2 Msamples. LAN and USB interfaces are standard. Silicon Chip is expecting to obtain an R7A4000series scope/spectrum analyser (another new product) for review in the near future. Celebrating 30 Years February 2018  63