Apr 20

My E3634A Mystery Explosion – WTF!

This is a short follow-up to a video where I was recently testing a Mayyuo M9711 DC Electronic Load (See Here) and I was using an Agilent E3634A Power Supply (which I previously fixed) as a power source. When I put the DC load into pulse mode within a few seconds the E3634A PSU exploded. What I heard was a loud pop, and a flash followed by a loud vibrating 50Hz hum, by which time I was able to reach the power switch and shut it down. I switched to another supply and continued with the test of the M9711 but today I thought I would open up (once agin) the E3634A and see what damage was done and what I found is a real mystery!

Did I imagine it all? Was there beer involved? Who knows, its a mystery!

Hope you enjoyed the video, catch you next time…

UPDATE – I found the smoke source

While tidying up I thought i would have a look at the two power MOSFET’s that failed and found the IRFP260 has a very small but visible smoke vent! I have added the photo’s below, I had to take these under the microscope x10 and x30 to see it. With the naked eye it looks like a light scratch.

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Apr 18

Maynuo M9711 DC Electronic Load – Unboxing, Teardown and Quick Test

I have been working on various power supply projects of late and was finding that my approach to loading PSU with simple incandescent laps was limiting. What I needed was a programmable DC load so I wondered – build or buy? Because I am already working on a PSU I decided that its probably better to buy one if I can find something that was reasonable quality and at a reasonable price. So I searched around and eventually took a chance on a Maynuo M9711 DC Electronic Load. I had not heard of the company before and could not find much out about them on on the internet, what I did see what that other similar devices that cost twice as much and had a reputable brand (BK Precision for example) were so similar in form that I thought its a good chance that they are different OEM’s of the same design. I am not sure that is the case because I do not have a BK Precision to compare, but I bought the M9711 brand new from the manufacturer on the basis that this was likely the case. Was I disappointed with the purchase? we shall see…

In this video I unbox and then tear down the Maynuo M9711 DC Electronic Load so we can take a look inside and see how it works and how well its been built. I try to explain how a DC electronic load works and I present a block diagram of the Maynuo M9711 based on my understanding and the cornerstone components that I find.

The main funcional components found in the device are:

Part Numner Description
Silicone Labs C8051F304 This is an 8051 based 8-bit flash micro controller, this is the main processor for the device
Texas Instruments ADS8327 This is a 16-bit SAR 500Khz Analog to Digital (ADC) voltage output converter, used to measure voltage and current in the load.
Texas Instruments DAC8831 This is a 16-bit Digital to Analog (DAC) converter, used to generate the programmable reference voltage.
Princeton Technology Corp. PT6314 This is a vacuum fluorescent display driver chip
International Rectifier IRFP250 The power MOSFET (x4 in 150W model) used as the main active power device that creates the load load

Notes and Diagrams

Below are the diagrams I present in the video describing the operation of a DC Load and the basic high-level layout of the M9711. You can browse these images or download a PDF document to print out if you prefer.


Well I hope you find this useful, thank you for reading and watching, catch you next time…

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Tibs are pocket-change for the internet™.