In a previous post I added a control knob to my Tenma 21-10130 Rework Station, but now I am taking a more detailed look at the controller board hardware inside paying particular attention to the microcontroller connections.
Removing the board from the rework station was a bit of a hassle, the screws at the bottom are particularly difficult to access. Eventually I had to unbolt the transformer from the case so I could get the screwdriver in, the transformer bracket catches up against a heatsink and capacitor so it cannot be completely gotten out of the way.
The board can be divided up into five sections, on the left is the mains power supply, with connections to the power switch and rework heater, along the bottom left is the 5V DC power supply for the microcontroller, top right is the control circuitry and connections for the rework heater and hot air, and bottom right those for the soldering iron. In the centre is the microcontroller and associated circuitry.
The rework heater, air pump and soldering iron are all controlled using triacs, these in turn are connected back to the microcontroller through optocouplers. The rework heater and air pump operate at mains voltage, 220V, while the soldering iron works at 24V, these are all using Alternating Current. Essentially the station is a collection of variable dimmer switches controlled by the microcontroller.
There are ten connections to the controller board
|CN1||Mains in – from power connector|
|CN3||220VAC out to transformer|
|CN5||Rework Air Pump power|
|CN6||Soldering Iron Temperature|
|CN7||Hand Key – Controls for Rework Wand|
|CN8||AC 9V input|
|CN9||Soldering Iron Power|
|CN10||AC 24V input|
The connectors CN5 and CN6 are used to provide sensing for the microcontroller; one for the soldering iron temperature and another from the rework wand with the button controls, in cradle detect, and temperature sensing, there is also a row of five onboard button switches.
With the multimeter in beep mode, tracing back the connections to the microcontroller took a couple of days.
The PIC19F916 microcontroller has 24 digital Input/Output pins which are divided into three ports of eight; RA0-RA7, RB0-RB7 and RC0-RC8. In the lists below I have shown the physical connection as well as the I/O port used.
The power control connections are to an optocoupler which in turn switches a triac:
|11||RC0||U6: MOC3083||TR1: BT136||220VAC||CN3|
|6||RA4||U5: MOC3083||TR2: JST139F||Rework Heater||CN4|
|16||RC5||U4: MOC3023||TR3: BT136||Rework Air Pump||CN5|
|7||RA5||U7: MOC3041||TR4: BT137||Soldering Iron||CN9|
After much tracing of circuitry I found the triacs to be connected to the optocouplers much as shown below. Resistor values vary and on the microcontroller connection side the current limiting resistor is on the low side, pin two, rather than on the 5V line.
There are five front panel control buttons which go low when pressed. Internal pullup resistors appear to have been used in the microcontroller.
|K4||25||RB4||Soldering Iron Power|
The two LCD displays, both are the same with seven connection pins with pin one at the top. The rework stations designers have not used the PIC’s built in LCD display functionality. The LCD panels are marked JRD90601A on the underside, I couldn’t find anything about this on Google.
|Conn||PIC Pin||PIC Pin||Purpose|
|5||15||RC4||14||RC3||Data 3 – LCD Select|
At present I have no information about the LCD data pins, I’m thinking that RC1 and RC2 could be Data/Clock while RC3 and RC4 is for selecting the LCD to send data to.
The Hand Key connector CN7 for the Rework Wand with pin one to the left when looking at the component side with the key notches uppermost. I have not opened the wand as it is sealed closed with glue and I did not want to damage it.
|1||n/a||GND for temperature|
|2||2||RA0||Rework Temperature – through OP07C op-amp|
|4||27||RB8||unknown – no connection?|
|8||n/a||GND for button controls|
|10||RA6||Buzzer – through Q2 (possibly a SS8550 PNP transistor)|
|9||RA7||U3: PC817 photocoupler – some kind of mains frequency monitor?|
|3||RA1||CN6: Soldering Iron Temperature – through op-amp OP07C|
|1||MCLR||Pulled high through 10K resistor – Master Clear Pin External Reset|
|21||RB0||9v AC monitor?|
This concludes the examination of the hardware connected to the microcontroller, further work needs to be done through software and oscilloscope observations to see how the LCD displays, power controls (probably PWM), and temperature sensors work and what the 9V AC and 220V AC monitors are doing.
Here are a couple of diagrams I drew up of the more involved sensor circuits while tracing things out. Values for the ceramic capacitors have been omitted as they are not marked on the SMD package. Both the rework and iron temperature sensors have similar op-amp circuits.
- PIC16F916 Microcontroller
- OP07C Single Bipolar Op-Amp
- Triacs: BT136, BT137 (no longer manufactured) and JST139F
- The MOC3083, MOC3023 and MOC3041 Triac optocouplers
- AT907-936B Tenma 21-10130 Rework Station
- SMD Markings http://www.s-manuals.com/smd/y2