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T-962A Reflow Oven Modifications

Modifications to a T-962A reflow oven which turn this cheap oven to a surprisingly effective piece of hardware.

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The T-962 and T-962A are low-cost reflow ovens used to solder surface mounted components to PCB boards. Their low cost makes them popular among hobbyists. It also means the quality is lacking. Many industrious individuals have come up with modifications that make these otherwise difficult to use ovens function far better. I dug through as much information as I could find on them, then selected the most promising features to investigate. This article walks you through all the options I considered, explains why I chose them, presents results, and provides sources.

The ideas I implemented were not mine and I give all credit to the generous individuals who have put in the work and shared it with us. This article builds on their work in two ways. First, it provides documentation of the best sources, saving others a lot of research work. Secondly, it fills in implementation details missing in other sources.

Which Oven to Buy

There are a handful of small reflow oven options.  I initially narrowed down the options to the T-962/T-962A mostly based on the large amount of information available. This meant having a baseline of knowledge and not having to discover it on my own.

The two ovens T-962 and T-962A are very similar with the main difference being that the “A” version is more powerful.  It has 4 heating elements as opposed to the two on the smaller model.  Many reported that the smaller model just barely had enough power to reflow, at best.  Some got it to work, some never did.  The larger “A” model has no shortage of issues, but it seemed like more people were having success (after a few modifications).  If an oven doesn’t have enough power, there isn’t much you can do.  The “A” version costs a little more, but gave a far better chance of success, so that's what I chose.

Further reading and I found out that there was an updated model of the T-962A.  I chose the updated model.  This turned out to be fortunate.  The new version seems to have corrected some of the issues with the older style.

I found two ways to spot the newer version.  The text listed it as “2020 New version"  and the exhaust port in the back is also different.

A link to what I purchased can be found in the Links section.

Sources

There are many good sources of information available on these ovens.  I narrowed the list down to what I believe are the three critical ones  that anyone wanting to modify these ovens should consult.  An overview is given here and the links can be found in the page Links section.

Unified Engineering Github Page

Unified Engineering created new firmware for the ovens.  The Github page contains the source code and binaries as well as instructions and notes on other modifications that have been reported helpful.

Seon, The Unexpected Maker

On Seon's YouTube he has a series of three videos on his T-962A.  The videos have some useful checks and modifications not on the Github page.  It is also very useful to see him step through things like upgrading his firmware.  The videos make a nice companion to the written steps on the Github page.

Jerry Walker's Investigation Series

On Jerry Walker's YouTube channel he does an entire series on his investigations on the performance of his oven.  He is exquisitely detailed in his investigations.  He uses professional-grade equipment to monitor the temperature distribution across the over during the entire heating cycle.  He considers several different techniques for improving the performance.  Each technique is tested for its benefit or lack thereof and then refined.

Modifications Considered

After reviewing a fair amount of the available information, the following list of modifications was considered the most important.  If the analysis of the modification concluded that the modification would be done, there is more information related to the implementation below in the Implementations section.

Grounding

Several owners reported that these machines are not grounded or not grounded well.  This is a potential safety hazard.

Analysis result: Recommend you check the grounding.

New Firmware

This modification results in a better user experience.  The user interface is cleaner and easier to use.  But, importantly, it added the ability to take advantage of the cold junction compensation.  This modification is fairly easy to do.  It is well documented in both writing and video.

Analysis result: Recommend doing.

Cold Junction Compensation

This modification lets the firmware adjust the temperature readings for the local conditions and makes the readings more accurate.  It is fairly easy to do.  It just requires a little soldering.  The firmware must be...

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  • Replace Masking Tape with Kapton Tape

    Lance10/16/2020 at 21:47 0 comments

    Introduction

    There are reports that the masking tape used on the inside gets too hot and starts to smell.  I ran the oven through one heat cycle with the masking tape and didn't notice the powerful odor reported.  The masking tape seems to on the outside of the insulation where it shouldn't get that hot.  While this is one of the most common modifications, it seems many people do it off of reports of an issue rather than having the experience themselves.  I tore my machine down more than most and found a couple of pieces of masking tape I had not seen reported before.  Most probably miss these pieces and yet experience no issues.  However, it is one of the easiest modifications and the effort could prevent a potential issue.

    Masking Tape Locations

    The main group of masking tape is apparent as soon as you take off the lid.  It covers the top of the insulation cover.

    The other two locations are ones I suspect most people miss.  To get to them you have to remove the insulation cover and the insulation.

    The second location for masking tape is on a strip that closes a gap just behind the top front lip.

    The third location is a strip of masking tape holding down a cover to the back fan.

  • Drawer Stand Offs

    Lance10/07/2020 at 21:52 0 comments

    Introduction

    Standoffs are used to keep the PCB off of the large metal drawer bottom.  This has two effects.  It results in a smaller contact area that prevents the drawer from acting like a heat sink.  It also raises the PCB up so that it is closer to the thermocouples and should make the temperature more accurate.

    Installation

    This is one of the simplest, and arguably most beneficial, modifications.  The screws are placed through the existing slots in the drawer bottom and tightened up.  You don't want to over tighten and damage the drawer, but I do recommend using tools and not just hand tightening.  Lock washers would be beneficial.  The repeated heat cycles have a tendency to loosen the screws.

    I used some #6 by 1 inch for the sole reason that I had some left over from another project.

  • Replace Side Fan

    Lance10/07/2020 at 21:16 0 comments

    Introduction

    The side fan is very noisy and runs whenever the unit is on.  An equivalent fan can be substituted  that is virtually silent.

    Original Fan

    I tracked down the specifications of the original fan.  The details, for reference, are below.  It's possible your fan is a different model, but the specs should be pretty much the same.

    • Sanyo SanAce40
    • Model number 9A0412J7D07
    • 40mm x 40mm axial fan
    • 15mm deep
    • 12v
    • 0.11A
    • 6.2 CFM
    • 28 dB
    • 7500 RPM
    • 2 wire

    New Fan

    The fan I selected is a Sunon Fans model 4129/HA40201V4-1000U-A99.  It is similar to the original with a few important differences.

    • 20mm deep
    • 5.5 CFM
    • 12.3dB

    In selecting this fan, I sacrificed a little CFM to get the quietest fan I could.   This fan is nearly perfectly quiet.  If I had to do it over again, I would try to get a little more airflow even at the expense of a little more noise.

    Installation

    The installation is easy enough, but there are two things you should be aware of.

    Bolts

    If you select a 20mm deep fan instead of a 15mm (like the original) it will fit, but you do need to replace the original screws with longer ones.  You will need 4 M4x30mm (0.7mm pitch) screws.

    Fan Connector

    Likely your new fan will come with a connector different than the one on  the existing fan (or it won't be long enough).  I chose to cut the old connector off and use it for the new fan.

  • Add External Access to ISP Header

    Lance10/07/2020 at 18:24 0 comments

    Introduction

    In order to update the firmware, you have to access the ISP header on control board.  This means removing the top of the oven which is rather inconvenient if you need to do it with any sort of frequency.  After running the oven a few times, I realized that I would probably have to update the firmware to add or modify heating profiles so I added an external connection to the ISP header to make this a simple process.

    There are some individuals that have chosen to install a USB to UART board in the oven and then have an external USB connection.  I didn't feel the need to sacrifice a board just for this purpose so I installed a wire pass through to connect to the pins I needed.

    Installation

    Design Requirements

    I decided on a few design requirements.

    • I didn't want loose wires hanging outside the oven so simply running a set of wires through the side wasn't an option.
    • I wanted to be able to plug my USB to UART board in directly without additional cables.  This meant I needed external make pins as my board has a female header installed.
    • The external pins should be protected from damage.
    • When plugged in, the external board shouldn't bend the pins and should be supported by the connection.
    • The installation should have a clean look.

    Design

    After scrounging around my parts bins to see what I had that could work, I came up with the following solution.  A stacking header would be used as the pass through connector.  The long pins of the stacking header give it the reach needed to pass through an enclosure and have plenty left over for connected to the USB to UART board.  On the inside, a custom jumper cable would be made to go from the stacking header to the ISP header on the oven controller.

    The stacking header would be housed inside a custom designed and 3D printed enclosure that could hold the header in place, provide a clean look, and have ledges to protect the pins and provide support for the USB to UART board.

    Installation

    I used a Dremel with a metal cutting wheel to cut through the tops of 4 vent slats in the side of the oven.  The opening was large enough for the center of the outside connector to pass but small enough that it was covered by the connector flanges.

    The stacking header was put inside the connector.  The two connector halves where sandwiched around the side of the oven and some cyanoacrylate glue used to stick everything together.

    With the connector installed, I made a custom cable to connect from the stacking header to the control board.  It uses some crimp style JST connectors: male for the stacking header side and female for the control board side.

    Resources

    If you want to use my connector, you can download it at the link below.  You can also access the Fusion 360 file and modify it as you see fit.

    There are two "Inside" pieces of the connector and you only use one.  One inside piece is general and allows you to access all the pins on the stacking header.

    The only inside piece is specifically for use with the Sparkfun board and blocks the unused pins.  If you use this piece, it has an orientation and you have to install the side with the "top" text towards the top of the oven.  You might be working on the oven lid upside down so don't confuse the orientation.

    Connector STLs:

    https://www.thingiverse.com/thing:4616526

    Fusion 360 Design Files:

    https://a360.co/36EwKsO

  • Back Fan Opening

    Lance10/06/2020 at 19:53 0 comments

    Introduction

    In Jerry Walker's videos, he concluded one of the most significant issue was that the back fan opening allowed cold air in during heating and sucked too much heat out during cooling.  He suggested partially closing the back fan entrance.  In the image below, you can see he has partially closed his off with Kapton tape.

    2020 New version

    In the updated version, they have added louvers to the back fan opening.  This provides and even better solution by nearly completely closing off the opening during heating and partially restricting the air flow during cooling.  The louvers are one big reason to make sure you look for the new version when you go to purchase your oven.

  • Cold Junction Compensation

    Lance09/29/2020 at 03:19 0 comments

    Introduction

    The cold junction modification adds a temperature sensor to measure the temperature at the board.  The new firmware uses this to correct the temperature readings from the thermocouples and make the heating process more accurate.

    Sources

    Cold junction compensation page:

    https://github.com/UnifiedEngineering/T-962-improvements/wiki

     Unexpected Maker video:

    https://youtu.be/HjYqSfLzBKk?t=119

    Note that Seon has his oven on the side so he doesn’t have to detach the cables.  However, if you put the top to the left side of oven (as opposed to the right as he has it) the cables reach (at least they did for my oven) and you can leave the oven flat.

    Hardware

    The temperature sensor I used can be found here:

    https://www.digikey.com/product-detail/en/maxim-integrated/DS18B20-/DS18B20--ND/956983

    When you read the datasheet it tells you that you need a 4.7kOhm resistor as well.  I used these:

    https://www.digikey.com/product-detail/en/yageo/RC0805FR-074K7L/311-4.70KCRCT-ND/730876

    If you use a different temperature sensor, make sure it meets the requirements of the new firmware and be sure to check the data sheet for wiring.

  • New Firmware

    Lance09/28/2020 at 20:34 0 comments

    Introduction

    If you have never upgraded firmware for a board before, this could be somewhat intimidating to some.  Largely because if you do it wrong, you risk bricking the hardware.  The manufacturer never intended the user to upgrade the firmware, so it isn't the simplest process.  However, the process is very well documented so with a little preparation, anyone should be able to handle it.

    There are various methods and tools to flash the firmware.  I will list the ones I used and verified that work.

    To start, be sure to read through the entire page for the firmware upgrade on the Unified Engineering page.  Also watch Seon's video on the upgrade.

    Firmware Github page:

    https://github.com/UnifiedEngineering/T-962-improvements/wiki/Flashing-the-LPC21xx-controller

    Seon's video:

    https://youtu.be/pIGK9VNppWw?t=40

    Notes on Required Resources

    To do the upgrade you will need the binary firmware file (hex file), software to transfer the binary file from your computer (Flashmagic), and a USB to serial converter.  Links to the hex file and Flashmagic software can be found on the firmware upgrade Github page.

    Getting the Hex File

    To find the hex file, go to the firmware Github page.  At the top of the page is a link for the latest releases.  Once you click the link, it may not be obvious where to get the hex file.  You need to click on the title for the latest release and that will take you to a page to download the file.

    Hardware

    You will need an USB to URT board.  There are many options available.  The one I used is linked below.  Please note that this board ships as 5 volt and you need to change it to 3.3 volt to use it with the T-962(A) control board.  Instructions for doing this are on the Sparkfun website.

    https://www.sparkfun.com/products/13263

    SparkFun FT231X Breakout

    Notes on Upgrade

    I won't go through the process step by step as the firmware page and Seon's video do a good job of that.  I will note some differences in the way I did things as it may be useful.

    Top Removal

    When Seon worked on his oven he had to tip the oven on its side to allow the top to sit flat on the table.  He had his top to the right of the oven.  I put the top on the left side and it would reach without tipping the oven.  I'm not sure if the side makes a difference or if the wires in my oven were longer.

    Breakout Board to ISP Header Hook Up

    I put my breakout board on a break board to prevent it from touching bare.  I taped the breakout board down so it wouldn't slide off the bread board.  The bread board was also used to ease the process of entering the firmware upgrade mode.  I could use a row on the break board to temporarily ground the n_ISP and n_RESET pins.  I have soldered a row of header pins on my USB to UART breakout board to make using it easier to use.  That isn't required, you could use the header at the end of the board normally used to connect to your device.

  • Grounding Check

    Lance09/28/2020 at 17:03 0 comments

    Several owners reported that these machines are not grounded well and this is a potential safety hazard.

    This seems to be one of the issues addressed, or at least partially address, in the “2020 New version.”   I tested the grounding and it seems to be grounded.  Inspecting the screw holes, there is still some residue that may prevent the best possible grounding, but there seems to be enough raw metal exposed to make an electrical connection between the different chassis parts.

    Use your multimeter or a continuity tester to check your machine.  You can watch Seon's video on checking and correcting this issue:

    https://www.youtube.com/watch?v=owd6Y_uy87E

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