Jul 08

HP 339A Teardown

A piece of equipment I use rarely but when I do I find really useful is my HP 339A Distortion Measurement Set. Built in the 70’s this unit has a precision sine wave oscillator and distortion measurement section. One of the things thats really nice is the oscillator and the notch filter are tied together and the notch filter auto-nulls to make measurements really easy to accomplish.

The build quality of this unit is impeccable, made by HP when they were making stuff properly. The entire chassis is made from folded high quality aluminium sheets with capture nuts and really precise machining. The main oscillator switches are coupled using a bar and wafer scheme but both the oscillator and the filter are fully screened and isolated in their own chassis sub-sections. The smell from inside the unit is that old-school electronics smell I used to encounter all the time when I was a kid taking apart old TV’s and Record Players. I don’t know what chemicals exactly make that smell but I am pretty sure if you could bottle it you could sell it – there is an idea for a unique aftershave! It could be called “Ye’old TV Man”!

Anyway, hope you will find the video interesting. Thanks for watching.

Jun 23

Omnitronic EDP 1000 Watt Class D Amplifier Teardown

Here I describe the basic operation and topology of a Class D amplifier and then tear down an Omnitronic 1000W amplifier to have a look and see what is inside. The big advantage of a Class D amplifier is the compactness and overall power efficiency. However, Class D amps are generally not used in High Fidelity application because of the limitations in dynamic range and distortion performance that can be achieved.

Here are the specifications scanned in from the user manual.

Hope the information is of some use. Thank you for watching.

May 25

HP 53131A Frequency Counter Teardown and Spillage Clean-Up

One of the instruments I have is a HP 53131A Frequency Counter, and putting the positives of this unit aside, its by far the most annoying bit of test gear I have! Why? well for some reason, when you apply power to the thing the fan runs even when its switched off. This is because the power switch is a soft switch and with just the AC cord plugged in the fan runs and makes the annoying fan noise. This is a really poor design and certainly not one of HP’s shining examples of engineering….I like to be able to switch my stuff off without reaching around the back and having to pull the power chord or unplug from the wall outlet – just plain crappy! HP what where you thinking?

I thought I would tear it down and have a look and see why this is, and perhaps see if there is any possible modification I could come up with to improve on this. When I took it apart I found a real mess of dust and some kind of substance spillage so a full clean-up was needed which somewhat distracted me from the power switch problem.

While its in bits, I also do a quick run through of the major components of the circuit and have a quick look at the power supply and power switch circuits in some detail.

UPDATE: The clean-up also appears to have resolved the strange trigger problems I had seen previously with this counter. Well pleased…

Here is the Agilent 53131A Component Level Manual including schematics for the frequency counter

Thanks for watching…

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…

Apr 16

HP/Agilent E3646A Power Supply Teardown & Repair

So I present the third in what is starting to feel like a long line of Agilent PSU repairs, but before you read on you should know that I have now depleted my collection of broken Agilent E36xx series power supplies so I will need to find another subject to blog about next time! That being said, even though I have blogged about two other PSU;s from the same family, I thought it would be worth videoing the repair exercise and at the same time try to demonstrate how I go about identifying and resolving a fault on this kind of circuit. The E3646A is a different model to the other two PSU’s I have repaired and blogged about – this one is a dual output 0-8v @ 5A / 0-20V @ 2.5A for each channel and the internals are different so I hope this will be of some use for anyone who may need to repair one of these.

Notes and Schematic Parts


You can download the Agilent E364xA Service Manual which include the schematics

I hope you find this useful or interesting. If you do please give the video a thumbs up and if you have any comments or suggestions please post them here and I will do my best to answer them.

Thanks for watching and catch you next time.

Apr 06

HP/Agilent E3634A Power Supply Teardown & Repair

Over a year ago now I repaired a HP/Agilent E3631A triple output PSU and have been using it very often ever since. Recently I bought an Agilent E3634A PSU which is a single output but high power supply, I bought it in non-working condition for not very much money (about $90). It turned out to be a non-trivial task, with physically burned out components and a difficult to track down and understand secondary problem. The components to repair the supply cost less that $20 and the repair exercise was challenging and educational so well worth the effort.


I decided that for this repair I would try doing a video teardown and repair which I have not done before. The repair took quite a few hours in the end, although I carried out the repair over about 4 weeks elapsed.

This is a really useful addition to my work bench, the high power nature of this supply makes it very useful for working in low voltage systems like audio amplifiers communications equipment and automotive applications that have high power requirements.

The Agilent E3634A Service Manual with schematics is available on the internet for download, I have provided a link here for convenience.

See you next time…