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I have recently built the Digital Effects Unit described in the February 1995 issue but cannot get it to function correctly. I am therefore wondering if you can shed any light on the prob­lem. The supply voltages appear OK, although the +16V rail actu­ ally reads about +17.5V at IC1 and IC2. When the unit is switched on, the two dashes are displayed OK but after that, the “delay” and “vibrato” rates are read out alternately on the display about once every second, with the “delay” LED flashing on each time the delay rate is displayed. The display values themselves are OK and correspond with the different DIP switch settings at power-up but no other switches/ the frequency of the sound, as though the roles of the ground and sensitivity controls are reversed. Yet, as I have said, I can see nothing wrong. If you can help me, I would really appreciate it. (B. D., Narooma, NSW). • We suspect that the ground control is not operating. Check that the wiper of VR3 does vary in voltage from 0.64VDC down to about 6mV as the potentiometer is rotated. A similar voltage should also be present at the pin 14 output of IC1b. The metal locator is operating correctly apart from the ground control problem. The sensitivity control will adjust the output tone since it amplifies the offset provided by the ground control. Speed regulation for model trains I have built myself a model train layout which has the tracks divided into 12 sections and incorporates a block system, preventing one train from running into the back of anoth­er. When the throttle is set, if one or more trains stop, the others speed up and this can cause derailments. After reading the September 1995 issue of SILICON CHIP on the Railpower Mk.2, I wondered if it were possible to incorporate this concept into my system. When the throttle is set, the trains functions appear to work; ie, none of the momentary switches do anything and the echo switch doesn’t do anything. Obviously, all connections and switches and switch orientations have been checked. All ICs appear to be seated correctly and in contact and all components are oriented correctly. Are you able to shed any light on the situation? (T. T., Auckland, NZ). • The vibrato switch, S7, or associated tracks leading to IC5 at pin 31, must be shorting to ground. Check the orientation of S7. The switch must be oriented with the “flat” to the bottom of the board as shown. Alternatively, the wiring between the PC boards should be tested for a short using a multimeter. Pin 31 of IC5 will be shorted to ground and show a low resistance reading. should run at the original setting. (R. W., Buderim, Qld). • If we are interpreting your letter correctly, it sounds as though your throttle circuits or your power supply have very poor regulation; ie, the voltage output varies depending on the size of the load. The simplest way to avoid this problem is to run each throttle from a separate power supply. In this way, there can be no interaction between throttle controls. Notes & Errata Railpower Mk II, September & October 1995: the component overlay diagram on page 33 shows a .0047µF MKT capacitor connect­ed to pin 10 of IC1. The capacitor’s value should be .047µF. Electric Fence Controller, July 1995: it has been brought to our attention that Australian Standard 3129-1981 for Electric Fence Controllers has been superseded by the new standard AS/NZS 3129.1:1993. This specifies a maximum fence output of 10kV com­ pared to the previous limit of 5kV. In order to increase the output of our Fence Controller to 10kV, we recommend changing the 6.8Ω 1W resistor in series with the ignition coil to 1.2Ω 0.5W. No other changes are necessary. AVICO POWER PRODUCTS APPROVED I E C CONNECTORS Avico Electronics now have available, a range of NSW Dept. of Energy approved “IEC” 3 PIN connectors. Features Include: • Rated at 240Vac 50Hz <at> 10A • 5mm wide solder or spade terminals • Clip or screw mounts • Integral fuse holder MODELS AVAILABLE IEC1 - Standard panel “clip mount” 3 pin Male socket......... RRP $1.45 IEC2 - Panel “screw mount” 3 pin Male socket............... RRP $1.45 IEC3 - Standard panel “clip mount” 3 pin male socket with fuse holder......... RRP $4.45 IEC4 - Panel “screw mount” 3 pin Male socket with fuse holder............... RRP $4.45 IEC5 - Standard panel “clip mount” 3 pin Female socket...... RRP$1.45 IEC6 - Panel “screw mount” 3 pin Female socket............ RRP $1.45 IEC7 - Dual socket panel “clip mount” 3 pin Male/Female......... RRP $4.95 IEC14 - Right angle plug screw terminating 10A 240Vac 3 pin Female plug.... RRP $2.95 IEC15 - Inline plug screw terminating 10A 240Vac 3 pin Female plug........ RRP $2.45 Imported and distributed by AVICO ELECTRONIC PTY LTD PHONE: (02) 624-7977 FAX: (02) 624-7143 Trade Enquiries Only ASK FOR AVICO PRODUCTS AT YOUR FAVOURITE ELECTRONICS RETAIL STORE Troubleshooting the Digital Effects Unit December 1995  91