## 送袋春畀你

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## Tektronix TDS 500~800 series Color CRT adjustments

For TDS 500~800 series, a batch of CRT driver boards, color and mono, regardless of how heavily they are used, have bad flyback transformers. After turning the unit on continuously for half a day, the screen might stretch and disappear.

If you have a matching CRT driver board with a CRT tube, I recommend instead of swapping the CRT driver (seemed more straightforward), extract the flyback transformer from the donor board instead. The reason is that the adjustments needed from replacing the flyback transformer is far less than re-tuning a different CRT driver board to match the tube.

It’s impossible to tune the CRT driver board while it is in the case, since the processor board covers it during operation (unless you have special cables for the Acq/Proc interface to replace the interconnect PCB card), it’s done ex-vivo like this:

I bought a ribbon cable extender and built a 2-pin jumper extender by salvaging them from CRT driver boards with toasted flyback transformers:

The first thing to check for is the +21V which is used to generate many voltages across the board (pun intended here): it affects brightness, scale, offset and linearity everywhere. If there’s any adjustments to be made, this need to be done first.

This voltage can be tapped by hooking the positive (red) lead to the center (output) pin of LM317 (3-pin linear regulator) at U90. If you have an alligator clip instead of a grabber, you can also hook it up to ‘pin 4’, which is the body of the regulator.

You can pick many spots for the ground pin. Since I’m using a grabber, I’d pick another big 3-pin IC sitting on a heatsink for the ground lead. In this case, it’s Q10, the transistor that drives the flyback transformer. It’s the pin nearest to the short edge of the board (behind the red lead, sorry):

Here’s a picture of blank board showing how many trimpots are there:

Only the brightness and contrast dials are documented in the service manual. The rest, I had to locate them in the schematic one by one.  Before that, I kind of figured out most of them by trial-and-error but had a few of them wrong, especially the voltages (there are three: +21V, screen and HV adj.): they all have the same effect. There are also some more obscure trims like center focus and horizontal focus (variable inductor). Now I know exactly what each dial does.

It’s hell of a lot of work to figure this out. I have some new old stock CRT straight from Tektronix at Beaverton, and it’s the reserve to support customers who bought color TDS 500~800 units from me. Almost all used units out there have problems (or going to have problems soon), and so far I’m the only one selling units with 1 year warranty (extendable to 3 years for extra).

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## Intercourse, PA

I know it’s childish, but I’d love to visit this town if I ever get to stop by PA.

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## Ching Chang in Supermarket

Found it in a Korean supermarket. Where’s Chong? Lol.

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## Python 3 Scientific Installation To-do List

Although I am a big fan of MATLAB, it’s time for me to really try out Python so I can fairly compare the pros and cons of both languages.

The first tiny hurdle for Python is its scattered installation process for Windows. I thought Python(x,y) will give me everything in one place, but turns out the Spyder is stuck in Python 2.7. To install Python 3.7, I’ll need to do it from scratch. Here are the steps:

1. Download official Python 3. You will need that for the “pip” package manager located in {python37}/scripts
2. Update PIP first to avoid complaints. You can run it anywhere in command prompt
python -m pip install --upgrade pip
You don’t call PIP to update PIP because you an executable cannot write itself in WindowsNote that for 32-bit Python, you might run into Python37\python.exe: No module named pip, so you might want to use ensurepip to bootstrap: python -m ensurepip
3. Now I’ll need Spyder3, a MATLAB-like IDE. Qt5 is one of the pre-req:
pip install PyQt5
4. And finally Spyder3
pip install Spyder
pip does not install icons in your start menu. So I’ll need to manually create a shortcut
{Python37}/Scripts/spyder3.exe
.py files are not associated with Spyder3 (normally it’ll just directly run the python script with python3). I usually manually change the association in Windows to Sypder3.
5. PyVISA is the analog of “Instrument Control Toolbox” in MATLAB.
pip install pyvisa
MATLAB’s Instrument Control Toobox also cover serial ports, which is done in Python by PySerial
pip install PySerial
6. Numpy is included with scipy:
pip install scipy
7. Turns out that only NumPy and IPython is installed with SciPy, not the entire ecosystem.
pip install pandas
pip install matplotlib
If you know the power of dataset/table objects in MATLAB like I do, you’ll jump for dataframes in panadas.
8. SymPy, the analog of MATLAB’s symoblic math toolbox, needs to be installed separately
pip install sympy
9. IPython gives the ‘notebook’ feel in Mathematica, MathCAD and Maple, where the returned results are directly pasted in the same area where your command/syntax is. I rarely cared for it because I usually want the max visual real estate for my plots.

Update: I tried Anaconda (2019.03, Python 3.7.3 x64) which supposedly have everything in one place, but the Spyder it included crashes right out of the box. Jyupter is confusing as it relies on the web-browser to render the results. Feels patchy and doesn’t look like it adds more than the steps above. Uninstalled it without hesitation.

Update: To update the packages, tack -U switch at the end of each of the above pip install commands. Remember to follow the order of dependencies (e.g. update PyQt5 before Spyder)

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## What is calibration? Hint: It is not adjustment!

Very often people doing R&D ask me if they need to have their oscilloscope calibrated. And for most of the time, my answer is no unless they need to have the NIST traceability or the calibration sticker to keep the regulatory bodies happy. They often thought it’s adjusting the calibration coefficients (or knobs) to make the unit more accurate. This is COMPLETELY WRONG.

In EEVBlog, they showed a video interview with Agilent Metrologist explaining what calibration actually does: it gives you the sample data points against trusted references about how your test instruments’ references has drifted between calibrations. Actually it’s preferable to not adjust the instruments if it’s already within specs.

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