Salvaging Electronic Parts - Part 4 Breville BFP650

Summary

This blog is the next in the series focusing on salvaging electronic parts. For this post, a Breville food processor was broken down with a view to salvage the AC motor.

Breville BFP650

Image courtesy www.productreview.com.au 

Salvaging
There were several plastic screws and individual plastic pieces which required removal from inside the food processor which allowed the microswitches, circuit board and motor to be removed.

Microswitches
Four micro-switches from Merchant Corporation were removed from the food processor. Three of the switches were interfaced to the push buttons seen of the outside of the Breville unit and the last switch was associated with the bowl interlock switch.

Breville BFP650 Micro-switches

Shown in the image above are the Merchant Corporation switches SM-51 and SM-31F from the Breville. The SM-31F switch features a short throw mechanical operation with a domed actuator top.

Circuit Board
The circuit board for interfacing the switches and controlling the motor is a single sided board. The switching relay manufacturer is from Tianbo Relay. There are associated passives for speed control and driving the power LED.

Breville BFP650 Control Circuit Board

The relay is sealed at the base with a bead of clear silicone; this part could be salvaged. The two power resistors and diode may be handy for spares however parts such as the M205 fuse may not be worth salvaging.

On the solder solder side of the circuit board there is a straight forward routing layout. A noteworthy item is the use of slots in the board to address cable management. Items to avoid are the undersized pads for cables and the excess use of solder on many of the joints.

Breville BFP650 Control Circuit Board Solder Side

AC Motor
The weight of the Breville unit appears mostly due to the copper windings of the 1000W motor. Manufactured by Chasekin Limited (HK), part number YXQ-250A33, there is no website for the company so details regarding the motor are scarce. Curiously, Breville list a 5 year warranty for the motor and all the other items have a 2 year warranty.

Breville BFP650 Motor

To take a closer look at the motor internals the plastic cover, water catcher and mounting plate required removal.

Breville BFP650 Motor Top View

With the mounting plate removed, the nuts holding the motor frame were visible.

Breville BFP650 Motor Mounting Plate Removed

The motor was further disassembled by removing the cover (end bell).

Breville BFP650 Motor Assembly

Visible in the image above is the rotor to the left, stator towards the bottom and end bell towards the top. Not pictured, but mounted on the side of the motor windings, was a thermal fuse.

The rotor was packed at the ends with a set of steel and fiber washers however no bearings were visible in the end bell. The fixture was removed and located inside was a steel bush. No bearings meant that this motor could not be used for extended periods of time.

Breville BFP650 Motor Bush

Salvaging parts from the Breville BFP650 was a misadventure and could be considered misspent time; for this particular product the author concurs.

Breville BFP650 Hardware

Some parts were salvaged from the Breville and the motor could be taken for metal recycling. The design and quality of the parts however, mostly prevent reuse for other purposes.

Salvaging electronic parts - Part 2 Spark Gaps

Summary

This blog is a continuation of a prior blog which illustrated the selection of electronic parts for salvage and basic component removal using a soldering iron.

Salvaging Designs
As used in the first part of the Salvaging Electronic blog, the same NESS security system (D8X D16X) control board will be used for the purposes of this blog. The content of this blog focuses more on salvaging, replicating or repurposing designs. When referring to designs this could be the schematic design, Printed Circuit Board (PCB) layout or both.

The section of Ness control PCB under examination in this blog was the sensor input. This area was chosen was to illustrate the schematic (resistors selection) and PCB design (on-board spark gaps).

Ness Sensor Input Section

The image above shows the passive components related to monitoring devices such as relay contacts (PIR sensors). 

A basic schematic representation of one of the input channels is shown below. Note that this hardware design operates in an analogue fashion. That is, the voltage on each sensor input is fed into an analogue switch (4051) and measured by the on-board controller. A break in the line between the externally connected sensor and the sensor input circuit changes the voltage measured.

Of interest in this design is the line facing input resistor (Rb) and the spark gaps (Ya).

Sensor Input Section

How is this design useful? 

When designing a product, with similar specifications, then referencing existing and proven designs can serve as a valuable baseline. This is not to say that newer solutions or devices should not be investigated thoroughly. Consider a product with a similar input requirements such as an external automated gate, marine access hatch monitor or cattle feed flow controller which may require external monitoring of a sensor. A similar input circuit would seem a logical choice. Could the input resistor Rb be exchanged with a standard thick film resistor (1206 footprint)?

Looking at a standard Panasonic 1206 resistor, this part is rated at a continuous 200V for a maximum power of 250mW. For steady state conditions this voltage and power handling would be more than suitable. In some systems, inputs can be subject to transient voltages as a result of external events which may be due to indirect lightning strikes for example. Using a single standard thick film resistor may not be the ideal choice for this solution. 

Undoubtedly for transient events, additional protection such as Varistors, Transorbs or other surge protection solutions are commonly used in conjunction with suitably rated circuit components. Inputs circuits are usually bolstered using devices designed for handling transients (Pulse Withstanding) such as Metal ELectrode Face (MELF) resistors. MELF devices from Vishay are such an example. The Vishay series MMA HV MELF in an 0204 footprint (1206 compatible), operates at a continuous 300V for a maximum power of 400mW. 
For the same footprint and small increase in cost, an input section can be made more robust. This provides the option of switching between standard vanilla and application specific components.

Salvaging Layouts
For the sensor input section, it was mentioned earlier that for transient events other surge protection solutions could be added to the design.

Ness Sensor Input Spark Gap

The Ness board has two solutions for line facing transients. One is circuit components (Yb and Yc) and the second is exposed PCB traces (Ya). Components Yb and Yc are most likely Varistors and Ya is an array of several spark gaps made possible by sections of PCB copper with solder mask removed. It should be noted that component Yb is not fitted to the board in lieu of Ya being 'on the fibreglass'. Certainly Varistors are more accurate for a rated breakdown voltage when compared to a spark gap and add cost to the board. 
A spark gap, as the name suggests, is a gap or distance between two points across which a transient voltage (spark) can discharge. The distance the spark can breach is a function of creep distance. Technical literature on this subject can be viewed at multiple sites such as EDN Access (basic) - ESD Protection for IO Ports, read on Stack Exchange, Wiley, PTR or the distance needed for a design can be calculated on www.creepage.com. Some understanding of material and contamination of PCB's is required.

For those needing a fundamental understanding of creepage, Paschen's law is a solid starting point.

Focusing on the Ness control PCB, the gap between the two spikes is somewhere around 1mm. Using the tables on the PTR website to determine a ballpark transient overvoltage, for a standard level two PCB contamination on FR4 PCB, yields approximately 400V.

In reality 400V is an extremely low voltage for arcing and only marginally above the theoretical 327V required to arc in one atmosphere of air, see Paschen's law. Regardless of the actual breakdown voltage of this design, some level of protection will be afforded to the design with the addition of spark gaps to the PCB. In any event component, Yc will bear the brunt of any residual voltage that the spark gap does not dissipate.

Adding Spark Gaps to a PCB
Depending on your drafting software of choice, the process to add spark gaps may differ from program to program. The subsequent method described requires only changes to the PCB file however, is not the only method for implementing spark gaps in a PCB design. Some designers may prefer to create the spark gap as a schematic / PCB component library pair or modify existing library components to facilitate the additions of spark gaps. Each method has its own merits and should be reviewed carefully.

The target design for adding spark gaps was the Solar MPPT Project designed in a previous blog. There are two external digital lines which provide communications between an MPPT and a Solar MPPT Controller. These TTL lines expose both the MPPT and Controller to transients and use only steering diodes for protection.

Existing Communications Port - No spark gap

A spark gap separation of 0.5mm was used for the purposes of illustration. For a specific design, the necessary calculations should be made to determine the correct separation.

Fortunately there are ample 0V connections on the existing communication connector. Other designs may need to make use of vias to provide the necessary return path for the transient event.

Top Layer Spark Gap Added

In the above image, a polygon was added to the solder side of the component - top layer. A single pair of terminals 'points' for the spark gap is sufficient if the chance of the design experiencing a transient event is low. For higher probability of transient events, then more points should be used where practical for the design.

Top Side Solder Mask Over Spark Gap

Following the addition of the copper to the board the solder mask must be excluded from the region used by the spark gaps. The capture above shows the spark gaps with the solder mask included.

Fill Added - Top Layer Solder Mask 

To exclude the solder mask, a fill was added to cover the area over and between the spark gap terminals.

Top Side Solder Mask Removed Over Spark Gap

Viewing the addition of the solder mask fill to the board shows the exclusion over the spark gap terminals. In some instances the PCB terminals are given a liberal coating of solder at the time of assembly. The main goal is to lengthen the lifespan of the terminals.

Whether components, an input design or PCB layout is recovered from the occasional tear down or salvage, the process can be well worth the exercise. 

Salvaging electronic parts - Part 1

Summary

Prompting this blog was my dismay which was caused during a recent scrounge through some component draws for a humble load resistor. The culprit is shown below, just an innocuous resistor right!

Old resistor

Before using the resistor a standard multimeter check was performed. This measurement indicated that the resistance was unexpected high resistance. After pulling lightly on the two legs of the resistor simultaneously the reason for the high resistance was apparent, mechanical failure. This faulty resistor would have been moved around in a draw of spare parts for the better part of ten years before it was used, possibly adding to its demise.

Old faulty resistor

Whether mechanical failure of the resistor occurred during manufacturing or more likely as a result of being mistreated during storage, this highlighted the limited shelf life for salvaged or even new electronic parts. Certainly some electronic parts are more susceptible to the rigors of handling, storage damage and part aging.

Salvaging Parts
This blog and subsequent blogs on the same subject, intend on showing some of the parts than can be salvaged from electronic equipment and possible issues that can be experienced with these parts. Whilst not all factors that damage electronic parts has been accounted for, the factors mentioned should serve as a guideline for those performing salvaging themselves.

A fully functioning control board from a NESS security system (D8X D16X) will serve as the example. For any board being salvaged a check with a multimeter can save the hassle of removing an already faulty component.

Ness alarm control board

The NESS control board has had the heatsink situated within the blue box shown above, however this was removed for visibility of surrounding components. In fact this heatsink would be considered the first salvaged part!

Power Supply

Within the bounds of the blue box shown in the image, are parts associated with a linear power supply. Parts to be salvaged could include the red varistors (V56ZA05P), DIP bridge rectifier, large electrolytic, linear regulator and associated surface mount capacitors.

Microcontroller

The red box identifies the alarm panel processor and another smaller power supply. Due to the age of the alarm panel board the processor, a Cypress Semiconductor MB89F538, this part is listed a obsolete which may preclude it being removed. The remaining crystal, fuse, DIP8 regulator, surface mount capacitors and logic level FET - BUK9245 could all be removed.

Line Out
For the telephone interface, shown by the yellow box, are parts such as optocouplers, a relay and an LMV324 rail to rail op amp. All these parts can be readily used in new projects.

Input Section
The input section has not been particularly noted for parts to salvage although the MELF and larger surface mount resistors come in useful for higher voltage designs. Of interest in this section is the PCB design itself and use or lack of components. More on spark gaps in a following blog.

Sections Not Noted
In the remaining sections are more logic level FET's BUK9245, ULN2803 driver and connectors would also come in useful when designing.

Salvaging Equipment
The tools required for removing salvaged electronics will vary depending on the equipment and budget. For most types of salvage work equipment such as needle nose pliers, SMT tweezers, a second gas or mains powered soldering iron and a range of drivers for different types of screws and bolts. On occasion equipment designers use TORX or HEX bolts to secure equipment.

As an example a computer power supply, which is commonly a single side circuit board, can be stripped of electronics using a soldering iron and a solder sucker or wick.

For circuit boards with tracks on both sides, with plated thru holes, desoldering can use more consumables such as solder wick especially for parts with multiple legs.

Surface mount components can be removed using additional equipment such as a soldering station with tweezers or a reflow oven can reduce issues relating to mechanical stress on electronic parts or over-heating when compared to using traditional solder wick. For the higher end user a hand held air convection tool offers timed temperature control however it is usually out of the price range for most hobbyists.

One noteworthy item not commented enough in other blogs for my liking, is the use of Personal Protective Equipment (PPE) when handling equipment made with lead based solder. This should not be taken as an alarmist comment although viewed as a simple measure to limit ones exposure to lead during the salvaging process.

Ansell cotton gloves

Workpiece Holding
When small to medium sized circuit boards, up to 150mm in width, are worked on for salvaging, a circuit board holder of any variety assists when changing between the component and solder sides of the board. 

Circuit board holder

For the salvaging process with the Ness control board a PCB holder from Altronics, T2356 shown above, was used.

Salvaging Components
To begin with the two and three pin components, with thru-hole (TH) leads, will be removed from the NESS board. As mentioned above these components consist of capacitors, varistors and regulators.

Flooding capacitor pins

Capacitor - Thru Hole
In order to transfer more heat from the soldering iron to the pad on the circuit board, adding a small amount of solder to the pads, of the part being removed, usually helps. The component can then be pulled and rocked out of its original position.

Capacitor removed

Excessive pulling force applied to the leads of the capacitor whilst desoldering may lead to the pins being partly lifted from the capacitor body. When a visible change is lead length can be seen, then the part should be discarded. Overheating a leaded capacitor is possible although unlikely in most instances. Many leaded capacitors have the maximum working temperature listed on the capacitor.

Regulator - Thru Hole
A similar method to the capacitor removal can also be applied to three terminal regulators such as the 78xx series.

Flooding regulator pins

As with the capacitor, it should be noted than one or more of the regulator pins may be connected to large PCB tracks, fills or entire planes on the circuit board. These larger areas of copper require more heating to melt the solder, so flooding the pins with some extra solder can facilitate a better transfer of heat from the soldering iron.

Regulator removed

Post removal the regulator, and similarly any other removed parts, would benefit with clean-up to remove the excess solder from the pins. A 78xx series leaded regulator from ST has a storage temperature of 150C, damaging these robust parts is also difficult.

Relay- Thru Hole
A through hole relay, which usually has 6 or more leads, can be removed with the old favourite desolder braid or a solder sucker.

Desoldering through hole relay

While using desolder braid to remove any electronic component, a fan or fume extractor is strongly recommended. Well known brand Weller has an article "Health Hazards From Inhaling and Exposure To Soldering Fumes" describing the risks of inhaling fumes created as a result of desoldering with braid.

Desoldered relay

One benefit of using the desolder braid is that during the process of desoldering, while the solder is being wicked from the solder joint, the position of the soldering iron tip can be moved around the component pin. This allows for cleanly desoldered pin and prevents the pin from sticking to the wall of the pad.

Surface Mount Components
Removing a surface mount component can pose its own difficulties. Some components can be glued, part of the reflow soldering process, or held to the board with Silastic for mechanical stability. In these instances removal of the component may require some more inventive solutions.

Capacitor - Surface Mount
For removal of a surface mount capacitor the soldering iron tip can usually be applied directly to the exposed pad of the capacitor to melt the solder and the component leg lifted away from the circuit board pad.

 Surface mount capacitor

To remove smaller capacitors, each of the exposed legs may need to be heated more than once and the part rocked free. This method is recommended because beneath the capacitor is a plastic former which holds the component flush with the circuit board. This plastic former can be melted if the soldering iron is kept on the component leg for several seconds.

Removed surface mount capacitor

Opto-Coupler - Surface Mount
For removal of a surface mount opto-coupler the soldering iron tip can used to heat the two circuit board pads located on one side of the component. There is usually more solder on the opto-coupler pads than components such as resistors and capacitors so additional solder should not be required.

Opto-coupler tweezer removal

A tip for removing these types of devices is to insert the arms of some stainless tweezers beneath the component. When the two pads on the same side of the device are heated, only a small amount of force is needed to lift the component from the circuit board.

Opto-coupler removed

The same technique is applied to the remaining fixed side of the component. Using the tweezers also allows removal of the heated component without the need to touch it directly.

MOSFET - Surface Mount
The last part to removed in this blog is a MOSFET in a DPAK case type. As with the opto-coupler using tweezers can be helpful to lift the component legs.

Desoldering leg of MOSFET

With no additional solder and the soldering iron applied to the leg of the MOSFET, only a small amount of force is needed to lift each component leg from the circuit board using the tweezers. It may also pay at this stage of the removal to use desolder wick to ensure that the legs of the MOSFET are in no way connected to the circuit board.

To heat the soldered tab of the MOSFET, adding some solder to the tab joint aids in heating the surface mount pad and MOSFET itself.

Heating MOSFET tab

Heating the device and the pad may take several seconds. When the solder near the tab begins to melt, applying horizontal force to the component usually allows the part to be slid off the pad. Heating the tab of the MOSFET for an extended time should be avoided.

Desoldered MOSFET

The maximum time a component should be heated can be based partly on the soldering process reflow curve. This curve is not always available from manufacturer data sheets especially for discrete devices so the peak temperature could also be used.

For the MOSFET that was removed from the NESS circuit board, BUK9245-55A, the device is several years old and the MOSFET 'storage temperature' of 175 degrees the only details listed.

BUK9245-55A Characteristics

As a general rule of thumb the solder reflow peak temperature should not be exceeded for more than 30 seconds. Applying this to the MOSFET removal, with a 260 degree soldering iron set temperature, then it should be safe to use 15 seconds of heating on such a device.

Finally as with any component it should be tested thoroughly before entering the confines of any spare part storage system!

Comair Rotron Fan Program Input - Control and monitoring of 4 Wire CD24R7X

Summary

This blog investigates control and speed monitoring of a 4 wire Comair Rotron fan using the Program input and Tacho output. The fan speed was controlled using a resistor then separately tested with an optocoupler driven by an external PWM signal.

Comair Fan Control Article

Tim Shafer, of Comair Roton, wrote a brief but helpful article relating to methods of fan speed control. This article is available on the Comair Rotron website or from Digi-Key as a PDF Document. The details from Tim were a start although did not clearly define methods of interfacing with the 'Program' input connection used by Comair Rotron fans. Even after reviewing the data sheet for the fan (CD24R7X) neither a suggested resistor range or recommended PWM frequency was suggested for the fan. Time for some bench testing and fan characterisation.

Comair Rotron CD24R7X

A test unit was purchased from Digi-Key and arrived in the Comair Rotron packaging. There was plenty of cardboard to secure the fan inside the box for transport which was a pleasant find in these times of bubble wrap packaging. The test unit was manufactured Dec 30th, 2015 with a serial number of 362.

Comair Fan Testing

Since the fan was earmarked as a test device to regulate temperature and air quality of a room, the range of fan speeds against changes in the Program input needed to be known. With the article from Tim Schafer in mind, the Program input was tested with an optocoupler driven from a signal generator then separately with a variable resistor. Additionally the effect of fan speed against variations in power supply voltage was also captured.

Comair Fan Test Setup

To perform the required tests, the fan was connected to a Rigol DP832 PSU and Function Generator, Agilent oscilloscope and vanilla multi-meter for current measurement verification.

The Comair fan tacho output connection (open collector) was pulled up to the 24VDC supply via a 220K resistor and then monitored by the oscilloscope.

The fan program input was connected to the optocoupler collector and emitter to 0VDC. To change the speed of the fan the Program input must be connected to 0VDC. The input LED of the opto was driven directly by the function generator.

Test Setup: Duty Cycle Measurements

Test 1: PWM Control

With a PWM frequency of 1kHz, the duty cycle was changed in fixed steps and plotted against the average fan current.

Duty Cycle against Fan DC Current

The duty cycle against the derived fan RPM was measured next. To derive the fan RPM, the frequency of the Tacho output was divided by two, since the fan produces 2 PPR - Pulses Per Revolution, then multiplied by sixty to convert into Pulses Per Minute aka RPM.

Duty Cycle against Fan RPM (Derived)

From tests performed on this fan, the speed changed from 1488 RPM at full speed down to 702 RPM at the lowest speed. This range of change in RPM equated to a change in duty cycle from 99% to 1%. 

One possible method to check the rotational speed of the fan, based on the duty cycle provided to the Program input, is the formula below which serves as a guide with a + 10% variation in the Tacho reading. A line of best fit was applied on test data from a single fan.

Estimated Fan Speed (RPM) = (7.9 x Duty Cycle) + 720

Where the duty cycle is the ON duration of the period as a percentage of the total period.

Test 2: Resistive Control

With a 100k variable resistor connected between the fan Program input and 0VDC, change in the fan tech output was recorded against changes in the resistance.

Test Setup: Resistance Measurements

Again the fan speed in RPM was derived from the 2 PPR Tacho output.

Program Resistance against Fan RPM (Derived)

The fan RPM varied from 1485 RPM down to 714 RPM which equated to approximately a resistance in the range of 12k to 0R. Tests were conducted with resistances over 20k with no change in the fan speed noted.

One possible method to check the rotational speed of the fan, based on a resistance between the Program input and 0VDC, is the formula below which serves as a guide with a + 6% variation in the Tacho reading. 
A line of best fit was applied on the measured data between 0 and 12k for the test fan giving the estimation below.

Estimated Fan Speed (RPM) = (0.068 x Resistance in Ohms) + 720 

Test 3: Power Supply Fluctuations

Lastly the DC supply to the fan was varied with PWM to determine the stall speed of the fan for a 1% duty cycle. It should be noted that when the supply was raised above 29VDC the fan speed became erratic. The recommended 28VDC limit listed on the unit by the manufacturer should not be exceeded.

DC supply Voltage against Fan DC Current

For the tests conducted with the fan the operational voltage range was found to be 16V to 28VDC with a stall voltage of approximately 6VDC.

Additional Measurements
The PWM frequency was varied in the range from 100Hz to 10kHz with some minor difference in the current drawn by the fan. A difference of 2% was noted between some of the duty cycle readings which may be attributed to instrumentation and or user measurement error.

As a matter of completeness the Tacho output was captured when the Program input was shorted to 0VDC, as shown below. This equated to approximately 717 RPM.

Tacho Output: Program Input Shorted to 0V

The Tacho output shown below was captured when the Program input was connected to a 100k potentiometer to 0VDC. The pot setting was at the highest resistance. This setting equated to 1428 RPM.

Tach Output: Program Input connected to 100k Potentiometer

Operating Specifications for the Comair Fan (Suggested) 
For the fan under test in this blog, the Comair Rotron CD24R7X, the suggested operating parameters are as detailed by the manufacturer with some additional information below.

Supply Voltage: 16 - 28VDC, Nominal 24VDC

Supply Current: Max 1.22A at 24VDC (Full Speed)

Fan Speed: 700-1490RPM + 5%

Program Input Resistance: 0R to 12k equating to slowest to fastest fan rotation. Estimated Fan RPM = (0.068 x Resistance in Ohms) + 720 

Program Input Frequency: PWM of 1kHz, duty cycle 1% to 100%. Estimated Fan Speed (RPM) = (7.9 x Duty Cycle) + 720

Tach Output: 2 PPR (Non-Isolated Open Collector) 28VDC at 20mA

Connections: Red           - 24VDC
                      Black         - 0VDC
                      Blue/White - Tacho Output
                      Yellow        - Program Input