Hey! This is another Flight Deck solution that is intended to use real avionics hardware to create a real flight simulator, in this case a Boeing 737-300.
Hey! I have a new Digital Chronometer from a Airbus A320, which is similar to the used in the Boeing 737.
The Unit...
Brand: Smith Industries
PN: 2610-13-1
Likely this unit doesn't work with AC power source, so a normal low DC power supply can be used between 24 and 28Vdc.
Lets see inside...
Here you will see the power supply of the device.
This board is providing 5V to the digital bus and aprox -24V (negative) to drive the LCD display.
And this is the processing unit.
Perpendicular to the processing unit and the power supply there is another board that has all the drivers of the LCD display (CD4056B).
This device is also providing an Arinc 429 output with all the information regarding the UTC time, Chronometer Information and Date.
Later I will evaluate the proper Arinc Labels that this unit is sending!!
Repare process...
The first time that I powered up this unit nothing was happening. I checked the power supply and was working nice and the microcontroller (MCU) was receiving the proper power feed.
After further checking I could see that the RESET signal of the MCU was active as pulses all the time, which is not ok... that means that the MCU is being reset periodically not giving it the chance to execute the code inside.
I did a schematic of the reset circuity and it was clear what was happening.
The signal /RES_IN is one pin of the TL7705 which is a Supply Voltage Supervisor used to manage the RESET condition of the MCU.
The circuit above is a very simple oscillator that generates RESET pulses.
If the MCU starts properly, the firmware is going to clear the proper pin which is going to produce the reset oscillator to stop, so then the circuit stops generating RESET pulses.
All of this was working properly, so then after this I could find the mayor issue... the main oscillator of the MCU was not working!!! so that means that the microcontroller was not able to execute any code.
A picture of the broken part:
So I couldn't find the original part, but this oscillator has a standard oscillation frequency (3.6864 MHz), thus it was easy to find a replacement.
Here you can see the board with the new part:
Due the fact that the footprint of the new oscillator was quite different I had to place it in other location... even better because it is closer to the MCU... kidding!
The Pinout...
So this is what I got after tracking the boards:
The Unit working...
First power up looking:
At this point the device is expecting that we introduce the first UTC data in order that the device can start working.
Chronometer function:
This feature starts pressing the button CHR ones.
If this button is pressed again the chronometer stops... pressing a third time will reset the counter.
Unit in normal operation during the flight:
The down-left switch is set in RUN position, that means that the Flight Timer is running, and this value is being shown in the ET display.
Ok.. I got two Engine Oil Quantity Indicators and this is the way to find them:
Brand: Simmonds Precision
PN: 10031-0000-01
Boeing PN: 10-60722-8
This how this part looks like:
This unit works with a power supply of 115V 400Hz and I believe that it is measuring the level of oil using the capacitance method, I'm really not sure at this point.
Let see inside:
As we can see it is a pure analog device.
After doing back engineering I could discover this pinout:
Again I don't have a picture of the oscilloscope when I tested this, but the pins 2 and 3 are 400Hz sinusoidal outputs.
The pin 3 provides a sine wave where the amplitude is proportional to the position of the pointer.
This signal is compared outside of the instrument with the signal provided by the pin 2, which is a fixed amplitude sine wave.
This time I'm doing some back engineering of this fuel quantity indicator.
Brand: BFGoodrich Aerospace
PN: 10037-4000-0213
The unit is pure digital and it is expecting much more than a capacitance at the input to measure the level of fuel.
The back draw if this unit is that it is totally sealed, so due the fact that I don't have any schematics of this I had to open it cutting the housing.
After tracking the electronic circuits I found out the following:
The testing circuit would be something like this:
This is what I got:
It was great to see the indicator displaying some data!! It toke me quite a lot to know how was working.
I don't have any record of the output signals in the pins 2 and 3, but I can tell that these two signals are quite complex and they are driving the probes that are installed in the fuel tanks.
I just got the second RDDMI as flown in a Boeing 767.
The reason why I'm using this specific instrument is because this uses Arinc 429 communication, which makes everything much easier when we need to talk with a computer.
The following picture shows the unit and can be found in the market as follows:
Brand: Collins
Type: RDMI-743
PN: 622-5001-107 or 622-5001-109
Good documentation can be found posted by another known person in this business that is building an amazing 767 simulator... please check the following link: Boeing 767 Sim and you will be amazed!!!
Some insights...
After powered it up and execute the BITE test I realized that the Left VOR/ADF pointer was not moving, so I had to disassemble it.
The unit housing is made of 4 independent parts. It got a mechanics compartment, a sliding cover for detach the power supply, a back cover that holds the main connector and the electronics board holder.
Lets see the pictures:
Back part:
So... to open it, first we remove the back part:
The back cover has the main 400Hz transformer as we can see here:
After the sliding cover taken out you will see something like this:
The sliding cover has attached the power supply:
Separating the motor and display drivers from the main system:
Finally we have access to the DC motors that drives the pointers.
Every part in this unit is modular, which makes very easy to access the different parts and repare them.
A closer look of the three DC motors modules:
Three screws need to be removed to be able to take apart one of this modules.
This is the DC motos module for the Right VOR/ADF pointer:
Due the encoder is attached to the reduction gear, special care should be taken to keep the shaft of the pointer in the same position that you toke it out:
Otherwise the pointer is not going to be at the proper position any longer.
Detaching the motor from the reduction gear:
It turned out that the shaft of the motor was a little bit jammed, probably because this unit was sitting in a warehouse for so long. The fact is that after gave it a turn, the motor was running very smooth again!! Problem solved!
Last thing to do is to clean everything before closing...
