LanceWhich 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 updated to take advantage of it, though.
Analysis result: Recommend doing.
Back Fan Opening
In Jerry Walker’s videos he came to the conclusion that restricting how much flow could go out the back fan can help significantly in smoothing out the cooling cycle. It prevented cycling between fan and heating elements as the fan overcorrected and caused the chamber to cool too fast.
This resistor plate also helped close off a large open space that let cool air in during the heat cycle. Restricting it helped with keeping the heat cycle on temperature and the distribution of heat in the chamber was more even.
Analysis result: Not required for "2020 New Version" (see log) but recommended for the older version.
Seal Gap at Drawer Front
This was another observation by Jerry Walker. He said that there was a large gap at the top of the drawer front that was allowing cold air in. He added an extension at the top of the drawer to close the gap. The "2020 New Version" seems to have closed this gap.
Analysis result: Not required for "2020 New Version" but recommended for the older version.
Add External Access to ISP Header
In order to update the firmware, you have to access the ISP header on control board. Initially, I did not anticipate having to update the firmware very often so it did not see worth the effort to create external access.
After running a few tests with the oven, I reconsidered and added external access. The firmware comes with a few decent heating profiles installed. It also has two custom profiles. It became clear this wouldn't be enough. Different types of solder paste and changing environmental conditions suggests more profiles will be required to get optimum performance.
Analysis result: Recommend doing.
Replace Side Fan
The side fan is very noisy and runs whenever the unit is on. An equivalent fan can be substituted that is virtually silent.
Analysis result: I decided to switch the fan, but there is no performance reason for doing so.
Drawer Stand Offs
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.
Analysis result: Recommend doing.
Replace Masking Tape with Kapton Tape
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 (see log). 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.
Analysis result: Recommend doing.
Add a Convection Fan
One of the biggest issues people report with these ovens is that some parts of their PCBs don't get hot enough to reflow the solder while other parts get so hot they components start to get burnt. In Jerry Walker's video series he adds and small convection fan and concludes this is one of the most beneficial modifications to prevent this issue. The fan does not need to generate a large circulation of airflow. It is just to mix up the air and prevent hot spots from forming. This was, by far, the most difficult modification by itself, but it also triggered a cascade of other modifications. See the log for the details.
Analysis result: Recommend doing.