Weather Station Troubleshooting

The manual for the ID-4001 gives a pretty good explanation of how the unit functions in the section 'Circuit Description'. I recommend reading it, if you haven't done so already.

Having worked on many of the ID-4001's and also having helped to design the replacement CPU adapter board, I've stumbled across several 'gotcha's'. It is my intent to try to document what I've found and hopefully save some of you some time.

Typically, if your unit is displaying all (or most) of the digits, it may not need a new processor. The display is multiplexed and requires the processor to be running in order to display more than one digit. If only one digit is displayed and it is exceptionally bright, then, odds are, you need a new processor. Next check the 50/60 Hz input pin to the Mostek CPU. This should show a nice square wave of the 'mains' frequency. If not, then either Q401 or that input pin on the CPU could be bad.

Check the power supply. If the unit is completely dead (no LED's at all), you probably don't have power somewhere.

If both indoor and outdoor temperatures read -40, and barometric pressure is 0.00 (or 29.00), then the V/F converter is probably not running. This is equivalent to reading all 0's by the CPU. All of the analog readings are converted to a frequency that can be read by the digital processor. The V/F converter is comprised of IC's U202, U203, and part of U207.

The V/F converter has a very wide range of operation and it is possible to move past the desired setting quickly on the Barometer adjustments.  Take care when turning the 'coarse' pressure adjustment.  It is best to adjust this using a frequency counter or oscilloscope measure pin 16 of the Atmel CPU using our 'Calibrate' function.  The actual range used for the Barometer is 280 - 305 Hz.  The range of the 'coarse' adjustment is from below 150 Hz to well over 800 Hz, so you ar trying to find a very small section of the adjustment.  If you don't have those tools, then center the 'Fine' control by turning it over 20 turns in one direction, then back 10 turns.  This should place it close to the center of adjustment.  Next adjust the 'Coarse' control 1/2 turn until you get a reading of close to 30.00 on the Barometer display.  You will have to wait for the ID-4001 to make its reading after each adjustment.

Make sure that both temperature sensors are connected.  When either of the temperature sensors are missing, the analog signal from the missing sensor moves outside of the normal operating range.  This can cause the analog switch (U207) to not be able to read one or more of the other inputs.  This can throw off the calibration, or even make the unit stop working.  This is a very common problem when working on the ID-4001.  Even if you are only working on the Barometric pressure circuit, a missing temperature sensor can cause troubleshooting problems.  If one of the temperature sensors is not working, this can also cause the analog switch to not function because the input from the bad temperature sensor may be outside the normal operating range.  Check the table below to see if both temperature senosrs are close to thier normal operating range.

The wind direction function does not use the CPU.  Remember this if you plan to use the RS-232 interface on our new board.  You must connect the 4-bits of the wind direciton from the ID-4001 to the 4 pins on our board.  The instructions included with the CPU board give more details on this.  The wind direction can be fully operational even though the processor is dead.  Wind speed does use the CPU and will not function if the CPU is bad.

Replacing the Processor

Follow the instructions included with the new CPU adapter board to replace your processor with our new one.  Remember to remove the 3.579 crystal, static RAM (U206), and the bias diode D205.  D205 should be replaced with a piece of wire. 


One of the nicest features of the new CPU adapter board is the addition of a 'Calibrate' mode.  Make certain that both temperature sensors are connected and turn the unit on.  You should see the time and temperature displayed on the front panel.

Hold the Clear button down until the time display reads CAL 1.  You can now cycle between CAL0, CAL1, and CAL2 by pressing the Clear button repeatedly.  You will notice that only the appropriate display is lit when the unit is in each of the calibrate modes.  This can help to ensure you are adjusting the right control during calibration.

Place the unit inCAL 0.  Connect a frequency counter or oscilloscope to pin 16 of the old Mostek CPU socket, or pin 16 of the new Atmel part on our adapter board.  Adjust the 'Coarse' pressure adjustment for approximately 290 Hz.  The barometer should display 30.00.  You should now be able to bring the adjustment to the correct setting using the 'Fine' adjustment.  If you need to use the 'Coarse' adjustment, don't turn it very far from the point where you measured 290 Hz.

Place the unit in either CAL 1 or CAL 2 mode.  Submerse both of the temperature sensors in an ice/water bath and allow them to stabilize in temperature.  With the Cal/Norm switch in the 'Cal' position, adjust the slope control to read approximately 400 Hz on the frequency counter.  Now adjust the other temperature sensor slope control likewise.  Remember to change theCAL function to the appropriate Indoor/Outdoor setting that you are adjusting.  Remove the temperature sensors from the ice/water bath and allow them to stabilize at room temperature.  Place the Cal/Norm switch in the "Norm" position and adjust the intercept control read the correct temperature.  Now adjust the other intercept control to also read the correct temperature.  See Alternate Temperature Calibration below.

This should complete the calibration of the analog portion of the ID-4001.  Hold down the Clear button again until the ID-4001 goes back into the normal operation mode.

The above calibration steps do not work when the ID-4001 is using the old Mostek CPU.  Our 'Calibration mode' will lock the ID-4001 into reading only one specific analog signal at a time, so you will be able to take the frequency measurement going to the CPU.  Since the Mostek part did not have this mode, constant switching between barometer, indoor temp and outdoor temp, causes the frequency to change and the reading to be invalid.

The following Voltage chart has been useful to me in troubleshooting the analog temperature circuits in the ID-4001.

                 Black Wire         White Wire          U201 (3)        U201 (1)       U201 (7)

32 (Cal)           2.71                   -4.26                   2.71             2.71            -4.86
32                   2.71                   -4.26                   0.36             0.36            -0.73
60                   2.84                   -4.14                   0.52             0.52            -0.96
85                   2.96                   -4.01                   0.68             0.68            -1.18

Alternate Temperature Calibration

Sometimes the 'Cal/Norm' switch will cause the ID-4001 to lock up reading -40 for both temperatures and either 29.00 or 0.00 on the barometer.  I have seen some of these switches so bad that they will also cause the latch-up problem even when stationary in the 'Norm' position.  Check this switch if you are having analog to frequency problems.

To avoid using this switch during calibration, use both a 'cold' and 'hot' source for calibration.  A bowl or glass of mixed ice and water will give a constant 32 degrees.  A second bowl or glass of water at about 100 degrees will provide the hot source.  Use a fairly good thermometer to monitor the 'hot' source.

Leave the switch in the 'Norm' position.  Place both temperature sensors in the 'cold' source and allow them to stabilize for a few minutes.  Then adjust the 'Intercept' controls to a reading of 32 degrees F.  Then place both temperature sensors in the 'hot' source and again allow them to stabilize.  Then adjust both 'slope' controls to reach the temperature of the water. 

These controls will interact with each other, so it will be necessary to go back and forth a few times. 

Can't get either 'Intercept' or 'Slope' to calibrate

First see if the problem is with the temperature probe or with the circuitry.  Temporarily swap the temperature sensors and see if that channel will now calibrate.  If it does, the problem is probably with the temperature sensor and not with the circuitry.

If it is not possible to achieve calibration, you can try changing the values of R204 (Outdoor) or R221 (Indoor) up or down to reach calibration of the 'Intercept' control.  Changing R208 (Outdoor) and R223 (Indoor) up or down, will affect the 'Slope' adjustment.  In some cases, I have had to change these resistors by as much as 5k Ohms.

If you have replaced the temperature sensors with my replacements

The original temperature sensors (single IC) did not draw quite as much current as the discrete replacement solution that I offer for sale.  The typical current consumption is within the specification of the ID-4001, however the maximum value is not.  Normally these will work in the application without any changes to the circuitry.  In some cases, it is necessary to provide additional current to the temperature sensor by changing the values of R201 (Outdoor), R216 (Indoor), R202 (Outdoor) and R217 (Indoor).  These should be changed in sets of R201/R202 and/or R216/R217.  I have found that replacing the 9100 Ohms with a 4700 Ohms and replacing the 6200 Ohms with a 2700 Ohms works in all cases.  If you have replaced the temperature sensors and can't get them to calibrate, try this first.  If you still can't get it to calibrate, then go on to fiddling with the other resistors as above (Can't get either 'Intercept' or 'Slope' to calibrate).


Input signals from Weather Boom

The LED's are wired like typical Christmas Tree lights, in series.  If one LED is open, then none of them will be working.  The voltage across the Black/White wires should be around 8 Volts.  If it is 15 Volts, then the circuit is definitely open somewhere.  This is a current limited 15 Volt source.  The current should be limited to about 20 mA with LED's or 38 mA when shorted.  Simply place a mA-meter across the two terminals and you should read about 38 mA.  This means that the 15V supply and current limiting resistor is good.  These are Infra-Red LED's and are not visible to the naked eye.  If you view them using a camcorder or digital camera, you should see them glowing.

The input signals from the weather boom should range between .5 Volts (Logic Low) to over 2.0 Volts (Logic High).  If the boom is not sending these values to the ID-4001, then the LED's or photo-transistors may be a problem.  If you are not quite reaching a 2.0 Volt level, then adjusting the LED and/or the photo-transistor may help.  Remove the two boards from the wind sensor body and re-assemble the two boards facing each other outside of the plastic, without the interrupter disk in the middle.  Make sure that each LED/phototransistor pair are facing directly into each other.  You may find by gently bending the LED and/or phototransistor, you are able to achieve a 2.0 Volt or greater output.  Be careful not to mechanically overstress the parts or they may break.

Also note that the wiring of the ID-4001 and ID-5001 booms is a bit different for the wind speed outputs.  The wind direction wiring is exactly the same for both.  Make certain that you are using the correct boom.

If you have purchased replacement LED's and/or photo-transistors from me, please note that the 'smokey' colored parts are the photo-transistors and the lightly tinted (yellow or pink) parts are the LED's.  It's best to not open the individual packages until you are ready to install them.

If you find that the encoder disk is scratched or rubbing on the LED's or photo-transistors, you can touch up the black portion of the disk using dark model paint.  Be sure to add the paint to the painted side of the plastic disk.  You can also add an additional # 6 lock washer on each of the mounting spacers, to add some extra space between the LED's and photo-transistors to keep them from rubbing in the future.  A rubbing plastic disk may also be caused by bad bearings if the lock washer trick doesn't work.

'Scratch' Test

For a quick test to see if the wind speed is working.  Remove the Green wire from the wind speed sensor screw, then use a small jumper wire to jumper from the Blue wire (+5 Volts) and 'scratch' the other end accross where the Green wire would be connected.  This 5 Volt noise should create a reading on the wind speed indicator.

Replacement 'Dummy' Temperature Sensor

Many people have asked me if there is a way to place a 'Dummy' temperature sensor on the ID-4001.  Here is a circuit that you can use to replace the actual temperature sensor while working on the ID-4001 or just to see if your problem is with the sensor or with the circuitry inside the box.  This uses a 10k Ohm linear control with a 6.8 Volt Zener diode across the outside terminals.  The white wire will go to the outside terminal where the Anode of the Zener is connected.  The black wire will go to the other outside terminal (Cathode), and the Shield will connect to the Wiper or center contact of the control.  This represents half of a bridge circuit.

This will look electrically like one of the temperature sensors.  Adjust the control to get about 3.0 Volts on the Black wire.  This will, of course, not respond to any changes in temperature.  Moving the control slightly, should cause the temperature to change.  You may want to use a 10-turn control, since very little change in voltage will cause a change in the reading.