TENMA Rework Station Teardown

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.

Controller Board, component side

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.

Wires Everywhere

There are ten connections to the controller board

Conn Purpose
CN1 Mains in – from power connector
CN2 Power Switch
CN3 220VAC out to transformer
CN4 Rework Heater
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.

Microcontroller Control

With the multimeter in beep mode, tracing back the connections to the microcontroller took a couple of days.

PIC16F916 pinout

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:

PIC Pin Optocoupler Triac Purpose Conn
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.

Optocoupler – Triac switch (from the MOC3043 datasheet)

There are five front panel control buttons which go low when pressed. Internal pullup resistors appear to have been used in the microcontroller.

Key PIC Pin Purpose
K3 24 RB3 Rework Power
K1 22 RB1 Up Button
K2 23 RB2 Down Button
K5 26 RB5 Set Button
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.

Rear of LCD display
LCD1
Rework
LCD2
Soldering
Conn PIC Pin PIC Pin Purpose
1 n/a 5V
2 n/a GND
3 13 RC2 13 RC2 Data 1
4 12 RC1 12 RC1 Data 2
5 15 RC4 14 RC3 Data 3 – LCD Select
6 n/a Backlight 5V
7 n/a Backlight GND

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.

Controller Board, LCD displays side

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.

CN7 PIC Pin Purpose
1 n/a GND for temperature
2 2 RA0 Rework Temperature – through OP07C op-amp
3 n/a GND
4 27 RB8 unknown – no connection?
5 18 RC7 Up Button
6 17 RC6 Down Button
7 28 RB7 Select Button
8 n/a GND for button controls

Other Connections

PIC Pin Purpose
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.

Rework Connections to the PIC16F916

Circuits

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.

Op-amp circuit for the soldering iron temprature
9V AC monitor circuit
220V AC monitor circuit

Datasheets

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