Salvaging electronic parts - Part 3 BenQ GL2430 Monitor

Summary

This blog continues a series of salvaging electronic parts, this time focusing on a BenQ model GL2430 monitor and what components could be salvaged. 

GL2430-B  BenQ Monitor

The monitor build date was from early 2011.

GL2430 Name Plate

Salvaging
The dismantling process for the monitor was skipped. The two major and two smaller printed circuit boards (PCB) removed from the monitor were: Flat panel driver board, Power supply board, Backlight driver board and Audio breakout board.

Flat panel driver board
Shown below is the flat panel driver board, single sided multilayer circuit board. This board contains the Realtek flat panel driver IC boxed in blue. Realtek part RTD2483RD. 

GL2430 Flat Panel Driver Board Top Side

Boxed in red of the image are a mixture of five serial memory devices ranging from ST Micro 24C02 EEPROM to a Winbond 2Mbit Flash W25X20. These devices are usually very easy to salvage.

Boxed in yellow are some of the numerous inductors on the board.

The semiconductor in the top right hand corner of the image is a Diodes Inc PAM8603 - 3W stereo class D amplifier. Possibly not worth salvaging as there are parts available with lower distortion ratings.

In the bottom left hand corner of the board are a pair of TVS arrays from the manufacturer InPaq 1045QU. Again probably not worth salvaging.

The crystal on the board is common video 14.318MHz type and could be repurposed if any crystal frequency is suitable.

Remaining on the board are a mixture of connectors, passives and unidentified semiconductors. If you were really scratching to find a MELF diode or 220uF Lelon Electrolytic then this board could be added to the spare parts box.

Power supply driver board
The power supply board is populated with components on both sides, double sided with a single layer PCB design. Heavy through hole components on the top side of the PCB and smattering of glued surface mount components on the solder side.

GL2430 Power Supply Board Top Side

Boxed in red is the mains common mode choke and towards the centre of the board, the switching transformer. Both these devices are manufactured by a Taiwanese transformer manufacturer. These parts can come in handy for research and design projects and a worth salvaging.

The green boxes highlight a few resistors which could be extracted for the spares bin. There are no signs of overheating or other physical damage which may have been caused by a fault on the PCB.

In the blue boxes are the diodes and bridge rectifiers. The bridge rectifier is listed as an obsolete part on supplier's websites such as Mouser so may be good for the spare parts box. The two larger axial diodes are Vishay part UG4B; a reputable brand worth salvaging once properly tested.

The two devices on heatsinks are the mains side switching MOSFET K4101 and secondary side dual rectifier diode FMX12S. At least one of these devices has discolouration in the PCB surrounding the heatsink. Heatsinks could be salvaged for other purposes.

Remaining on the top side of the board are various connectors, mains voltage rated varistors and mixture of capacitors. Usually components which have been operating at mains voltages for an unknown amount of time can left on the PCB if the operational state of these parts is unknown.

GL2430 Power Supply Board Bottom Side

Shown above is the solder side of the power supply board. To the left of the image is the switch mode controller. Across the board are a number of other parts, all glued down with epoxy. Using epoxy to glue surface mount components in order to simplify the assembly process is standard practice. The epoxy can make repair and salvaging parts difficult.

Backlight driver board
Below is an image of the backlight driver board. The main LED driver, boxed in red, is an MP3389 from Monolithic Power. Device is worth salvaging or even the entire board itself as it is a self-contained unit which could easily be reused.

GL2430 Backlight Board Top Side

Boxed in blue is an unbranded inductor which is always good to have in the spares box.

Shown in the yellow box is a SinoPower MOSFET APM1110 which was not located on the company website. Specifications are nothing to be excited over although part would be worth salvaging for prototyping.

The remaining passives such as the radial capacitors are from Lelon making the remainder of the board a contender for the spares box.

Audio Connector board
Lastly is the small 3.5mm audio connector board. The connectors are a standard pinout and could be salvaged or the entire board repurposed for a bespoke project.

GL2430 Audio Connector Board Top Side

Design Notes
A section of the power supply mains input section was chosen for some brief notes on PCB design.

GL2430 Power Supply Board Main Input Section

Boxed in white, top left hand corner of the above image, is the one of the mounting holes with exposed long pads coated in solder. This is a good feature for eliminating star or copper washers however the electrical resistivity can suffer due to the smaller contact area and surface oxidisation of the solder. It should be noted that on the component side of the board is a through hole nut allowing direct access to the mains earth connection.

In the orange boxes are several slots on the board to improve the creep distance between component pins. Slots in the board are an effective and cheaper solution to conformal coating.

Shown in the blue box is attention to detail by the PCB designer. A small pullback was applied to the copper surrounding the two mounting holes for the IEC mains connector.

Boxed in purple is a section of silk screen showing the isolation plane between mains AC and isolated DC voltages. The silk screen for the isolation plane and most components is present on both sides of the PCB making component identification and servicing easier.

Lastly the red box shows three cascaded surface mount resistors used in series to discharge the mains input capacitor connected between active and neutral. The PCB designer was mindful of creep distance and to some degree spacing between these components.

Beta Layout Reflow Controller with Sunbeam BT2600 Mini Bake and Grill for Reflow Soldering

Summary
While designing a prototype circuit for an LED torch it became apparent that many of the white LED controllers were surface mount leadless devices. Many of these devices have exposed pads meaning that standard soldering with an iron can be difficult.

It is possible to solder smaller devices with exposed pads by directly applying the heat beneath the device through thermal vias in the PCB, or use the oven in the household kitchen to reflow, however neither of these are ideal solutions.

Reflow Controller
Beta Layout have for some time sold a Reflow Controller. This controller (Version2) has been reviewed with the Severin oven which Beta Layout provides however there are no reviews for ovens available locally in Australia. 

Beta Layout V2 Reflow Controller

At the time of writing the Beta Layout controller sold for €119 plus shipping. There are a number of kits and Arduino style solutions on the web although for an off the shelf solution this was worth trying the controller with a locally available oven to determine suitability for home reflow soldering.

Reflow Oven
The only factor determining the oven to choose was the maximum load of the reflow controller which, for the version two model, is 1500W.

Searching the local market results in a grill from Sunbeam BT2600 with elements top and bottom. The oven retails from the GoodGuys for just under $60 AUD.

Sunbeam BT2600 Oven

Noteworthy Items
It should be noted that as the controller is European made the associated mains plug and socket suit the European market. No option to order an Australian plug to female IEC plug or male IEC to Australian socket.

Oven and Reflow Controller Learn Cycle
Beta Layout's controller is for the most part plug and go. On the hardware side there is the main AC power, oven AC power and the thermocouple. 

A learning cycle must be completed before the controller can be used. The thermocouple can readily be lashed to a dummy PCB (spare leaded components or enamelled copper wire) and placed in the most central position inside the oven.

Sunbeam BT2600 Oven Inside

With the door down the upper and lower heating elements are easily visible. On the front control panel the oven is switched to 240C and the timer set to OFF.

The dummy PCB is placed in the middle of the oven, door closed, power ON and the learning process is ready to start.

Test PCB for Learning Cycle

Once the learning button is pressed the oven comes to the required temperature and then the oven switches off. Subsequently it should be noted that the oven was left running standalone, in the garage, for an additional 10 min to reduce some of the VOCs. Time for a test board.

Test Board and Oven Temperature Profile

For the reflow tests the same PCB is used. A few resistor pad pairs are cleaned with flux, solder paste added and surface mount resistors applied. To apply the solder paste without a stencil, a syringe with a 0.5mm needle allows a relatively clean and controlled application of the paste.

With the PCB placed in the middle of the oven, the door is closed and the solder button is pressed on the controller. The thermocouple was left attached to the test PCB.

Beta Layout Controller - Preheat Stage

Several minutes later the reflow process has completed and the oven has cooled down sufficiently that the PCB can be checked.

Test PCB after Reflow

Inspecting the PCB, all joints to the resistors are clean and the component alignment is good - not faultless. Changes to the profile may help eliminate some bubbling on the joints.

Before operating the oven again the RS232 port on the controller is connected to a laptop and a standard terminal program, TeraTerm. Using the controllers interface the automatic temperature measurements were configured to be output at 5 second intervals. A number of cycles were run across the day as the ambient temperature increased.

Below are the graphed profiles of the oven with some minor variation in the starting ambient temperature.

Reflow Oven Temperature Profile

Several subsequent tests using the oven yielded repeatable reflow results with similar sized PCB's. Reducing the oven thermostat from 240C to 210C made little difference to the results however reducing the thermostat to 190C caused issues with proper wetting and should be avoided.

Shortly after the reflow cycle was complete the door of the oven was opened and a thermal image taken. Some of the heat has already escaped from the opening of the door.

BT2600 thermal image shortly after reflow

The temperature profile used by the controller can be manually configured through the serial interface using a terminal program. 

In summary this combination of controller and oven is a valuable addition to the prototyping hardware setup which can yield excellent results for the home hobbyist.

Arlec 19 LED Lantern Torch upgrade with brighter LED's (45 lumen)

Summary
This blog illustrates one possible upgrade to the Arlec 19 LED lantern torch with the aim of upgrading the LED's, using a white LED driver to make the light output more consistent as the battery voltage decreases and extracting more life from the 6V lantern battery if possible.

Arlec LED Torch

Sections in this blog:

1. Reason For Upgrade
2. Lantern Battery
3. LED Circuit
4. Benchmark
5. Upgrading The Design
6. Selecting New Components
7. Schematic Design
8. PCB Design
9. Populated PCB
10. Comparison New and Old
11. Downloads

Reason For Upgrade
There is a noticeable difference in the light intensity between this Arlec model and my older single bulb style Eveready Dolphin. The LED torch does the job for illuminating items close up, certainly no complaints there. When the Arlec was initially purchased the light output was more than acceptable with the 6V battery giving it's all. After sporadic use over a few months the light intensity simply dropped off. Time to investigate why and if this can be remedied.


Lantern Battery
When the torch was purchased it is supplied with an Arlec 6V Lantern Battery. The Arlec battery follows the standard 6V 11Ah design and is comprised internally of 4 separate F size batteries. The Eveready Super Heavy Duty 6V Lantern battery datasheet can be used as a comparison as Arlec don't appear to publish a datasheet.

Eveready Super Heavy Duty 6V Lantern Battery Discharge Curve

Assuming a total LED current of 100mA and a constant current discharge, by using the discharge curve for a 3V cut off the torch will operate for almost 100 hours. This does not match up to the tens of hours the torch actually lasted for.

Over the expected 100 hours of operation, including self-discharge, the battery voltage will gradually decrease, meaning that depending on the circuit design the life of the torch will be somewhat less. To determine how much less it's time to look at the existing circuit and the battery together.


Battery Open Circuit Voltages
Firstly is the battery itself. This is comprised of four series F size batteries which can be considered flat at 0.8V under load (industry standard). This gives a terminal voltage of 3.2V.

For a known flat 6V lantern battery the unloaded terminal voltage is 5.67V. Looks great unloaded right. Connecting the LED circuit board the battery terminal voltage drops of 2.55V almost immediately then continues to drop at a rate of 0.1V every five or so seconds, this is too flat to be useable. Again removing the load and the battery recovers to 5.5V.

LED Circuit
The LED's themselves, the current driven through the LED and importantly the forward voltage drop of the LED itself.

Unscrewing the torch allows the back of the circuit board to be seen. The circuit board, shown below, can be removed from the front housing by unscrewing four screws.

From a quick visual inspection there appears to be two LED strings across the battery (after the ON switch). Two 33R resistors limit the current to two separate LED strings, one with 9 LED's and the other with 10 LED's. For each string of LED's all devices are connected in parallel.

Arlec LED Torch PCB

Benchmark
To gather some metrics the LED board was powered from a benchtop power supply.

With a 6V output from the power supply the terminal voltage at the rear of the circuit board was 5.975V.

Active LED Torch PCB

The power supply displayed 0.193A and the first string with 9 LED's in parallel had 2.86V forward voltage the second string with 10 LED's had a forward voltage of 2.83V.

Arlec PCB on Power supply

When the power supply voltage is slowly reduced from 6V the light intensity appears just useable to 4.5V however reduced further to 3.5V this barely lights a small room.

Upgrading The Design

There are a few upgrades that can be made to the design.

1. LED Driver: For the battery voltage between 4.5V and the discharged battery voltage of 3.2V there is some capacity left in the cells.
   In order to use this capacity the LED's must be driven in a different manner that is not using resistors, or at least resistors that are very small in value or keep losses to a minimum.
   One of the common methods for driving white LED's is by using a constant current source. There are a number of benefits by using a constant current design of which a relatively constant drive to the LED's can produce a more consistent light output over the range of the battery voltage when compared to using simply resistors.
2. LED Type: In the discrete LED market the big player names of CREE and Nichia will sound familiar to those in the field. There are other tier LED manufacturers such as Optek, Line-On and Everlight to name a few.
   Certainly it would be surprising if the LED's used for the torch were CREE. Regardless it does not hurt to look for an LED with a better specification.
3. LED Viewing Angle: Be it from me to suggest that a torch should resemble a spotlight in light pattern, on the other hand why waste light on objects you are not looking at. To that effect, selecting an LED with a narrow viewing angle of 15 degrees will be more effective as a torch instead of using an LED with a 120 degree viewing angle.
4. Other Smarts: There are other designs online for torch retrofits with LED's with pulse width modulation, low battery cut out or using a single higher power LED device.
   Although pulsed LED's do have a higher efficiency when used with higher currents the low steady current used by torch would negate this gain. Again testing is the best way to validate this so a separate adjustable timer can be added to the design.

Selecting New Components

The constant current design for the LED's could be achieved with some discrete components and to solve the LED drive issue when the battery voltage drops, a boost converter can be used. This comes at a cost to the remaining battery capacity and no boost converter is perfect in the conversion.

Rather than build this design using discrete components a dedicated LED driver with a boost converter can be used with a handful of external parts. Chip manufacturers such as Texas Instruments (TI), Linear Technology and Micrel all have ready to solder solutions which will suit this application.


LED Driver
To select the new LED driver from the hundreds of devices found on Digikey, Mouser, Element14, RS Components and more it pays to detail a list of requirements which can be used to focus the search.
For this design the driver should have: 

1. Input voltage range of 3V to 7V
2. Capacity to drive a number of white LED's in series (string). This relates to the output voltage that can be generated by the boost converter
3. Switching current to drive a number of strings, 3 in this design, at a current of 20mA per string
4. Price, current consumption of the actual LED driver and flatness of the LED driver efficiency against the actual battery voltage are other factors to also keep in mind

EDIT
The TPS61160 was initially selected and tested, however due to the LED string design in this circuit, the operation was unstable. A more expensive device was chosen which was the LT1618EMS. Essentially the white LED driver design shown in the datasheet was used with a change to the 2.49R resistor used for current limiting.

LT1618 Datasheet Circuit Example (Courtesy Linear Technology)

White LED

Sorting through supplier's websites, component suppliers and blogs can be somewhat daunting. One novel site that summarised the essentials of LED's can be found on Gizmology. 
The Gizmology website contains a section on luminous intensity, which is the standard measurement for low power discrete LED's, and the conversion to luminous flux which was one of the factors used to select a replacement LED for this design.

Below is a sample of some of the comparisons made:

1. Everlight, Part# 334-15/F1C2-1VWA, Angle 20 degrees, 14625mcd typical
2. Cree, Part# C512A-WNN-CZ0B0151, Angle 25 degrees, 15850mcd typical
3. Marl (Nichia), Part# NSPW500DS, Angle 20 degrees, 27000mcd typical
4. Cree, Part# C503D-WAN-CCBEB151, Angle 15 degrees, 35000mcd typical

Glancing at the list item 4, Cree C503D, looks like the device to choose surely. However using an online calculator the luminous flux was calculated for beam angles giving a different result:

1. Everlight, Angle 20 degrees, 14625mcd, 1.396 lumen
2. Cree, Angle 25 degrees, 15850mcd, 2.360 lumen
3. Marl, Angle 20 degrees, 27000mcd, 2.577 lumen
4. Cree, Angle 15 degrees, 35000mcd, 1.88 lumen

No surprise that the Marl device, which was also the most expensive by 7 times compared to its closest rival, also has the highest luminous flux.

Now a twist in the selection criteria was the ranking or binning system used by most LED manufacturers. This sorts LED's by a number of physical characteristics. For the Marl (Nichia) device, which appeared to be a V ranked part, the minimum luminous intensity shows 22000mcd and maximum 31000mcd.

Listing the minimum luminous intensity and corresponding flux:

1. Everlight, Angle 20 degrees, 11250mcd min, 1.074 lumen
2. Cree, Angle 25 degrees, 8200mcd min, 1.221 lumen
3. Marl, Angle 20 degrees, 22000mcd min, 2.099 lumen
4. Cree, Angle 15 degrees, 16800mcd min, 0.903 lumen

For the limited budget of one dollar, the CREE C512A series was a cost effective option. Plenty of surface mount white LED's would outperform this thru hole LED. The usage of surface mount is a different circuit board technology (Al-Core).

The C512A CREE LED had a standard 3.2V forward voltage at a current of 20mA. Instead of retaining the 19 LED design the number of LED's was reduced to a even 18 such that split strings were able to be used. With these details the boost converter components were calculated.

Schematic Design

Added to the white LED driver design in an optional PWM circuit. It could be interesting to map out LED brightness against continuous current.

Updated LED Circuit with LT1618

A low power 555 timer is wired in an astable configuration with some additional diodes to give a wider control over the PWM operational range. Either a pot or resistor is fitted between the discharge and trigger pins allowing the PWM to be manually adjusted or permanently set.


PCB Design
Before beginning the PCB layout the size of the board, mounting holes and LED positions are measured from the existing Arlec design.

PCB Mechanical Properties

The four mounting holes were measured, albeit rather crudely with a steel ruler and the corresponding middle LED position used to determine a radius for the outer two rings of LED's. On the PCB this detail was added to one of the mechanical layers. Individual LED positions were added as small crosses to aid in component placement.

Next the bulb connection is added and LED's which are placed at a 45 degree angles to simplify the routing.

PCB LED Placement

A top layer fill was added to provide mechanical stability and routing for the LED driver.

PCB Top Layer Route

PCB Bottom Layer Route

Shown below is the board viewed from the front in 3D.

PCB 3D Front View

The rear of the PCB fully loaded with the white LED controller, optional timer and bulb mount to suit the existing torch hardware. There is a single wire connection from the tip of the bulb to a through hole pad connection on the board.

PCB Final Route in 3D

After a final component placement, board clearance and PCB design rule check the PCB is sent off to 3PCB for manufacture.

Populated PCB

Below is the populated PCB mounted on the reflector.

Populated PCB Front View (mounted on reflector)

Populated PCB Rear View (mounted on reflector)

Comparison New and Old

Without having a Lux meter to compare, both boards were directed at a wall with a 1m between the boards, 1m away from the wall, with no other light sources. The reflector was not fitted to either board and the result is easily visible.

Comparison Improved and Original Boards (without reflector)

Fittingly the new board also draws less current at 6V, 160mA compared to the older board drawing 195mA. This is a saving of almost 18% although as the battery voltage drops the current drawn by the LED driver continues to increase.

Comparison Original and Improved Boards (current consumption)

The LED driver will run down to 2.6V on the bench power supply while drawing 700mA although at this time the lantern battery is probably well and truly dead!

Downloads

Schematic Rev D

Altium PCB File

Top Layer as DXF

Bottom Layer as DXF