1 INTRODUCTION Some Amiga 2000s have a problem: the battery backed up clock does not keep accurate time (it is not uncommon for the clock to gain a minute or two a day). This problem is easily fixed. The battery backed up clock has an adjustment screw which allows you to adjust the clock using a miniature screw driver. The problem in adjusting the clock is that you need a reference source to calibrate the clock against. Although you may have observed that your clock runs fast or slow by some number of minutes each day, that doesn't tell you how much you should turn the adjustment screw. If you had access to the tools used to calibrate electronic watches you would be able to tune your Amiga's clock without trouble. Since such tools are rare, most people have had to resort to trial and error to calibrate their Amiga's clock. I have provided an alternative to trial and error: I have written a program that compares the battery backed up clock against an independent timer in the Amiga that is based on the alternating current that powers your Amiga 2000. The Amiga has several timers in addition to the battery backed up clock. One of these timers is a line frequency clock that "ticks" every time the alternating current completes a cycle (that is it ticks 60 times a second for North America and 50 times a second for Europe). My program, called Calibrate, checks the time of the battery backed up clock against the line frequency clock every ten seconds and displays the results. This gives you almost instant feedback which allows you to adjust the battery backed up clock much more accurately. The Calibrate program can be used either from the Workbench or the CLI. It can be used if your Amiga's power source is 60 cycles per second or 50 cycles per second. The only tools you need are a medium Phillips head screwdriver (in order to open your Amiga 2000's case) and a small jeweler's screwdriver (to turn the adjustment screw). The small jeweler's screwdriver should have a blade that is only about a sixteenth of an inch wide. Screwdrivers of this type are sold for working on eye glasses; also, most Radio Shack stores carry a set that contains three miniature screw drivers of different sizes. Before I adjusted my clock, it would gain two minutes a day. After I adjusted the clock with the help of the Calibrate program, it loses a few seconds a week. (Luck played a part in this success.) 2 THE CALIBRATE PROGRAM If you wish to use Calibrate from the Workbench and your country does not use 60 cycles per second alternating current, you will need to edit the tool types stored in the Calibrate icon. To do this, click once on the Calibrate icon to highlight it. Then select the "Info" menu item from the "Workbench" menu. In the "Tool Types" portion of the Info Window, you will see a line that looks like "hertz=60". Page 2 Click on this line and edit it to reflect the power line frequency of your country (if you don't have 60 cycles per second power you probably have 50 cycles per second power). Then click on the "Save" gadget on the lower left corner of the window. After you have set up the icon for the Calibrate program, you can run it from the Workbench by double clicking on its icon. To run the Calibrate program from the CLI, simply type the command run calibrate and press return. If you live in a country that does not use 60 cycles per second alternating current, specify the frequency of your electricity after the "calibrate" in the command. For example, run calibrate 50 Regardless of how you run the Calibrate program, it will open its own window to display its results. This window will have the standard "close", "window to front" and "window to back" gadgets. Next to the front and back gadgets is a orange and black gadget labeled "Restart". This gadget can be used to start a new round of testing without having to exit the program and run it again. In the window will be three columns of information. The first column is the elapsed time as measured by the line frequency clock. This time will be displayed in units of ticks since testing began. Remember, this clock ticks once for each cycle in the AC current. So a reading of 600 means 10 seconds for North America. The numbers in this column should increase by 10 seconds worth of ticks every line. The second column is the cumulative absolute error between the line frequency clock and the battery backed up clock. As is the number in the first column, this number is measured in ticks. A positive number means that the battery backed up clock is gaining time relative to the line frequency clock. A negative number means the battery backed up clock is losing time. Typically, this number will slowly increase or decrease as the test continues. The third column is the cumulative relative error between the line frequency clock and the battery backed up clock. This number is displayed as a ten thousandth of a percent. In other words, a reading of 1/10000% is a relative error of one part in one million. Thus, If your clock shows a relative error of 100/10000%, it will gain about nine seconds a day. The Calibrate program will display a line of results every ten seconds. At any time you may click on the "Restart" gadget to zero the elapsed time and restart the calculations of the absolute and relative errors. The Calibrate program multitasks well. It does not take over control of the whole Amiga or do anything that compromises the integrity of the operating system. However, it does run at a moderately high Page 3 priority (priority 5) relative to most other programs. Normally, a program that runs at a high priority will keep normal programs from running. Calibrate does not do this because it spends most of its time asleep. Calibrate sleeps for ten seconds, then spends a half second computing and displaying its results, and then goes back to sleep. During the ten seconds that Calibrate is asleep, other programs on the Amiga will run normally. During the half second that Calibrate is computing its results, most programs will seem to freeze. Do not let this bother you: those programs will resume at the end of the half second as if they had never been interrupted. Although you may run other programs at the same time you run Calibrate, Calibrate's measurements may be more accurate if it is the only program running. (The effect that other programs have on Calibrate's measurements depends on what the other programs are doing and their priority.) For the most accurate results, Calibrate should be the only program running. Since Calibrate does not interfere with the system, you may want to try running it before attempting to calibrate your battery backed up clock to become familiar with its display and controls. You may also want to run it a few days after calibrating your clock in order to check its accuracy. The line frequency clock that Calibrate reads in order to do its job is actually "owned" my the Amiga's operating system. Since Calibrate only reads the value of this clock, it does not interfere with the operating system. However, since the operating system is using that clock for its own purposes, the operating system sometimes interferes with Calibrate. About every ten to fifteen minutes, the operating system will alter the setting of the line frequency clock behind Calibrate's back. This means that Calibrate will report terribly wrong results about every fifteen minutes. If Calibrate seems to be reporting erroneous results, click on the "Restart" gadget to start testing over. 3 ADJUSTING THE BATTERY BACKED UP CLOCK Turn your Amiga and its monitor off. If your monitor is setting on your Amiga, take it off and set it to the side. Unplug the keyboard and mouse for your Amiga. Remove the five screws that attach your Amiga's case. Two of the screws are on the right bottom edge of the Amiga. Two more are on the left bottom edge of the Amiga. The fifth screw is in the middle top of the back of the Amiga next to the fan. Remove the case by gently sliding the case forward. If you feel the case hang, it may be catching on wires in the Amiga. If this happens, try tipping the back of the case up a little bit so that it clears the Page 4 wires. WARNING: Once the case is off the Amiga, it becomes sensitive to static electricity. Do not touch any of the circuit boards in the Amiga. A simple touch could destroy the Amiga. Plug the keyboard and mouse back into the Amiga. Boot your Amiga with the case off. Run the Calibrate program. Locate the adjustment screw for the battery backed up clock. Standing in front of the Amiga, the housing for disk drives will be on your right hand side. Just to the left of the drive bays, will be the first slot of your Amiga. This slot is the CPU expansion slot for plugging in a 68020 board to speed up your Amiga. Between the end of the CPU slot and the front of the Amiga is the small variable capacitor used for tuning the clock. This capacitor is labeled VC800, and on my Amiga is colored bright yellow. This capacitor is a small cylinder with a small screw in its center. This screw is used to adjust the battery backed up clock. If the absolute and relative errors shown by Calibrate are positive, your clock is gaining time. To make it run slower, turn the screw clockwise. If the absolute and relative errors shown by Calibrate are negative, your clock is losing time. To make it run faster, turn the screw counterclockwise. When I was adjusting my clock, it appeared that the adjustment range of the screw was only 90 degrees. Turning the screw more than 90 degrees merely puts you in a different quadrant were a clockwise turn in that quadrant slows the clock and a counterclockwise turn speeds it up. So, do not turn the screw more than 90 degrees. After you adjust the screw, wait a few seconds, click on the Restart gadget in the Calibrate window. The reason for waiting a few seconds is that the clock seems to behave erratically for a few seconds after adjustment. After you click on the Restart gadget, the Calibrate program will display the statistics on the newly adjusted clock. After a few lines of measurements are displayed, you may want to make further adjustments to the clock. After you are satisfied with the accuracy of your battery backed up clock, turn your Amiga and monitor off, unplug the mouse and keyboard, and replace the cover. Reboot your Amiga. Set the time, and use the SETCLOCK OPT SAVE command to save the time to the battery backed up clock. Later on, after a few days pass, you may want to compare the time stored by your Page 5 battery backed up clock to the correct time. This is the best method to check the accuracy of the battery backed up clock. 4 ACCURACY OF THE CALIBRATE PROGRAM The Calibrate program may not allow you to adjust the clock as accurately as you might like. The major problem is the accuracy of the power line frequency. Averaged over the period of a day the line frequency is extremely accurate (otherwise electric clocks would gain or lose time every day). However, over the course of a few minutes the frequency may be slightly off. For example, as small a change as the line frequency being only 59.994 cycles per second instead of 60 cycles per second when you calibrate your clock will result in a nine second per day error in your clock. After calibrating my clock, comparing the time after week long intervals showed that it was accurate to about a second a day. However, if I ran the Calibrate program at certain times of the day, the program would report relative errors that predicted a twenty second a day miscalibration. At other times of the day, the Calibrate program would report relative errors that showed my clock to be perfectly accurate. Once, the Calibrate program showed absolute errors that were positive and increasing for awhile, then the errors would decrease to zero and then become negative; finally, the absolute errors would began increasing until zero and then become positive again. The absolute errors described as sine wave with period of about a hundred seconds! The conclusion: I had adjusted my clock to be more accurate than the power line frequency when measured over short periods of time. This meant that I could now use the Calibrate program to find the errors in the line frequency on the basis of the battery backed up clock rather than vice versa! Even if the power line frequency is perfectly accurate, each measurement of Calibrate program could be off by one tick. This means that you should not make an adjustment simply on the results of one or two lines from the program. After making an adjustment, allow the program to run for a few minutes to confirm the trends in the statistics displayed.