Aging problem just from storage Working 6632B stored for 10 years has a failed tantalum cap

I fired up one of my 6632B stored for almost 10 years and smelled burned electronics, despite everything is functioning. I tested the unit immediately when I bought them a decade ago and it was working fine, so it’s an example where electronics can deteriorate by storing (even in temperature controlled, dry environment).

Since I see smoke, I turned everything off immediately and investigated. Turns out one of the tantalum capacitors in the processor/controller board gave in:

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Wobbling rotary encoder in Agilent/HP/Keysight 6630B series 6631B, 6632B, 6633B, 6634B, 6634A, 6635A, 66332A*

6630 series system power supply is sturdy as a rock, but has a rotary encoder sticking out that it’s almost guaranteed to wobble if you buy it used.

I thought they would have known better to secure the rotary encoder with a nut so it won’t wobble (HP usually does a perfect job making their designs reliable. This one is a rare miss), so I opened it up to see what I can do about it.

My initial guess was that the solder joints were weakened as it was used to mechanically support external forces for users of the dial. But I was wrong. Here’s what I’ve found:

The weak metal strip retainers gave in and the whole rotary encoder is about to break loose! The encoder was actually still functioning before I opened the case up. So HP assumed their vendor for the mechanical rotary encoder did a good job withstanding frequent wiggling. Apparently their vendor completely failed them: the metal retainer design was hopelessly flimsy that I wouldn’t even consider using it even in light-usage applications! FAIL!

There’s a huge number of these high quality power supplies on the market because Motorola/Nokia closed down their massive operations, flooding the market with 6632Bs for years to come.

I’ll now strengthen (I came up with a solid technique to make sure the dial will never fall apart again) the 6632Bs I have for sale to businesses that needs a perfect unit (which I sell for $699/ea). If you are a hobbyist, feel free to send me a message and I’ll tell you how to do it, provided that you do not share it with anybody else (I’ll trust you). If you are a business, I can restore 6630B series to a professionally salable state starting at $499.

* Note that I included 66332A despite it’s a mobile communication DC source (66300 series) here because the guts of it is actually 6630 series. Every other 66300 series (3 Amps max) or less has a different form factor (that’s more like a 33120A) and the only odd one out of the series is 6632A (5 Amps max).

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Explain XOR tricks succinctly with two properties Change detector, toggler

Most teaching materials on XOR starts from its straight definition then a bunch of recipes for exploiting XOR. It is not convenient to remember and not intuitive to come up with new tricks on our own. Instead, I’d like to describe XOR as two intuitive operations:

  1. Change detector (The logic definition itself)
  2. Toggling light switches (Flipping twice undoes it)

The second interpretation (toggling) is actually way more powerful and easy to remember than the first interpretation (definition).

With the toggling interpretation, you don’t have to think hard to come up with the four algebraic properties:

  1. Associativity and commutativity: we only care about whether the individual light switches (bits) are flipped odd (flipped) or even (not-flipped) number of times at the end of the day. When it happens in what order does not matter.
  2. Identity: flipping NONE of the switches (a mask of all 0) leaves it alone
  3. Inverse: pick only the switches that are already turned on (using itself as mask) and flip them (xor) guarantees to turn everything off (0)

The XOR swap trick can be constructed by exploiting the fact that flipping the same switch twice (at any point) reverts it back to where it started:

x y
Start x_0 y_0
Mix y_0 with x_0 x_1 = x_0 \oplus y_0 No info is lost, still have y_0 somewhere to undo if we wish.
The incumbent y_0 is used to cancel the y_0 inside x_1 to recover x_0 \begin{array}{rcl} y_2 & = & y_0 \oplus x_1 \\ & = & y_0 \oplus (x_0 \oplus y_0)\\ & = & x_0 \end{array} Since y_0 is already saved (mixed with) x_1, we don’t have to worry about losing it as long as we get to our main goal of putting x_0 in y, which will be used as a recovery key later.
Now use the x_0 stored in y_2 to unmix x_1 to recover y_0 \begin{array}{rcl} x_3 & = & x_1 \oplus y_2 \\ & = & (x_0 \oplus y_0) \oplus x_0\\ & = & y_0 \end{array}

Note that this trick is obsolete for modern computer architecture because

  • it enforces strict dependence that kills any predictive pipeline (speedup) in modern computer architecture, and
  • will yield zero all the time if you try to swap with itself in-place (same memory location), which is wrong because you expect the swap to do nothing.

Adding a check for the degenerate case (self-swap) slows the program down even further, making it worse than using a temporary storage for swapping. Therefore there’s no good reason to use it unless you have an exotic use case.

This is mainly used as a teaching device (or homework problem) to teach that XOR-ing even instances of the same variable in the chain cancels it.


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Malware deleting TrustedInstaller.exe, therefore crippling Windows

My sister’s computer is was infected with a bunch of stubborn malware. Even after cleaning the offending files, a lot of things won’t wouldn’t work.

Windows Update, run sfc /scannow, or DISM /Online /Cleanup-Image fails with unknown reasons, which I found it somehow related to “Windows Module Installer” service not running.

I saw something weird in services.msc: “Windows Module Installer” doesn’t exist, but I know the underlying name is “TrustedIntaller” and noticed a service named as such is there, but it cannot be started, nor there are any descriptive information.

So I searched registry for “TrustedInstaller” and got to its entry. I noticed these two:


It means the meaningful names and descriptions I saw on services.msc are generated by calling the underlying  service executable file with switches. I checked my “C:\Windows\servicing” and found that “TrustedInstaller.exe” is not there at all! Of course you cannot start a service where the file does not exist at the promised path (ImagePath).

I searched the hard drive and found only one instance of the file stored somewhere (like C:\Windows\winsxs\x86_microsoft-windows-trustedinstaller_31bf3856ad364e35_6.1.7600.16385_none_90e389a7ae7a4b6c) and I tried to move the file to “C:\Windows\servicing”. However the ownership and permissions to write to “C:\Windows\servicing” goes to “TrustedInstaller” account, not “Administrator”, so I took the ownership, gave Administrator full rights, then move the file over.

Everything worked after that! Just the mere trick of deleting TrustedInstaller.exe is enough to make the user miserable trying to clean the system up! “sfc /scannow” or the like requires TrustedInstaller/WIM to be working in the first place, so you cannot use it to repair TrustedInstaller/WIM problems.

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Floppy Disk Drive Ribbon Cable Orientation

Hooking up a floppy drive after a decade of disuse today, I followed the notch/key on the connector/cable but it turns out to be incorrect! Turns out I should do the opposite, forcing the key to the side without the notch, by force (or trim the key)!

So stick with the conventional wisdom that the ribbon’s pin 1 (marked) should always stay close to the power connector, regardless of whether it’s IDE or FDD (3.5″ or 5.25″), EVEN IF FOOLPROOF MECHANISMS TELLS YOU OTHERWISE!




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Option 005 “Vertical Output” port of 54600 series oscilloscopes (54616B, 54616C, etc) A secret backdoor feature that new oscilloscopes lack

Over the last year, I got a couple of requests for 54616B that specifically ask for a “vertical output” port at the back. I have never seen an oscilloscope that came with such a port, including a few hundred of first generation first generation 54600s I acquired from many different sources.

I got curious and looked it up. Turns out it’s a secondary feature of a relatively obscure option (only measured in the manuals, but I have never seen one) called Option 005, which lets you analyze (like count lines) and trigger over common TV signals, like PAL/NTSC/SECAM, which is way obsolete today. It also seems that none of the customers asking specifically for the “vertical output” port at the back know that it is a super rare option that is normally not included, so they must be using it for something else other than analog TV signal analysis.

A closer look at the user guide shows that “vertical output” port duplicates the signal source (e.g. channel 1) that the scope is triggering on, limited to what is seen by the oscilloscope, to the said “vertical output” port, a secondary feature to let you chain your signal to instruments like spectrum analyzers for further analysis.

I tried the feature myself by chaining the output to another oscilloscope. Even if the waveform is off-screen for the current vertical volts/div, the vertical output port waveform did not clip. I also played around with input impedance settings 1MΩ and 50Ω for a 50Mhz square wave. Based on what gets the square wave badly distorted, I can confirm that the vertical output signal is the analog signal after attenuator (the amplitude changes only with Volts/div that causes relay clicks) but before ADC, assuming a 50Ω load.

Wait! An oscilloscope that duplicates the input analog signals after being processed by the front end (post-attenuator, pre-ADC) to an external output port?! I don’t have to mess with the original signal path by splitting the signal (passively) or make an amplifier to duplicate the signal? Wow! How come it’s not standard (or at least a purchasable option) in modern oscilloscopes? I’d like to see what’s going on with the analog waveform before the scope processes it! Not only it’s very educational, it allows other instruments to get an accurate insight of what the oscilloscope is seeing. Neat!

Installing the Option 005 is not difficult if you happen to have an unobtainium Option 005 case with labels, and the entire kit with all the necessary interconnect. However, it’s like an unicorn and I’ve never seen one. Drilling professional looking holes for it is a nightmare as we don’t have the dimensions. The hardware is also insanely hard to get as it was made for a specialized crowd for the time and practically nobody cared about analog TV signals nowadays. Even if I can get that, they are most often missing the interconnects. The ribbon cable is missing for nearly all of them, and if you get a standard ribbon cable, you’ll realize the plastic retainer gets into the way of a screw on the main acquisition board so the Option 005 card won’t slide in unless you trim some of the plastic off. PITA!

Nowadays I am already spoiled by high end gears like MSO6054A and 13Ghz Infiniiums (like DSO81304A), but none of them has a convenient analog, post-attenuator output like a first generation 54600 with an Option 005. Given the hardware is scarce, I’ll save it for the top of the line first generation 54600 series, namely 54616B and 54616C.

For those who have this special need (need to tap into the pre-ADC signals up to 500Mhz), I can custom build these Option 005 units for you, depending on parts availability. Call me at 949-682-8145 or reach me at my business website

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Agilent (formerly HP, now Keysight) vs Tektronix

I am much more inclined towards Agilent than Tektronix because

  • There’s nothing a Tek scope can do that an Agilent can’t
  • Agilent’s user interface is very intuitive that it requires little to no trial-and-error or RTFM.
  • Agilent’s people is very generous about helping customers out even if support is discontinued. Tek gets rid of all service information and software after discontinuation by policy.
  • Agilent’s gears are very thoughtfully designed and is a pleasure to service, for the ones that I have opened up so far. Tek designed their unit to live barely enough through their support lifecycle, hoping they won’t have to service it.
  • Agilent’s old gears lives much longer. Just look at (even better, open up) Agilent 54600 series and the damn TDS 300~800 series and you’ll see what a nightmare Tek is.
  • Tek’s autoscale algorithm is a piece of garbage!
    Even with TDS6000B/C series that cost tens of thousand of dollars at the time of writing still couldn’t figure out the top Ghz signals and give you a long Time/Div that completely aliases the signal and therefore confuse the heck out of their users. Not to mention Tek’s autoscale is sometimes too dumb to figure out which one channel you are on so that you have to move to (highlight/focus on) the right channel. Never had to deal with this kind of nonsense while using an Agilent scope.
  • Agilent’s gears also have much fewer hard/painful to fix aging problem than Tek.
  • When Tek scope fails, it’s often followed by a bunch of other unrelated aging problems. The capacitors are not designed to stand the heat for 10 years of usage.

There is Lecroy, but there are much fewer old gears in circulation and I don’t like their user interface much either, but at least the dials won’t take more than half a second to respond like Tek. I once asked Lecroy if they can generously share the schematic for an old unit like Agilent and they sent me one. At least they are not being a d**k about it like Tek.

I have both used Agilent and Tek scopes for sale, but my own bench is all Agilent whenever there’s a choice. Tek is OK if you plan out a difficult measurement setup (for documentation or manufacturing), but miserable if you are poking around to troubleshoot (that’s what I use the gears for). I sell Tek just to cater those who have been brainwashed because Tek got the first-mover advantage back in the days.

Of course my bias is based on their Tek’s gears in the digital age. I heard that they were very good at the analog scope times, so that might be the reason why Tek still have a strong following. HP/Agilent/Keysight pretty much nailed the digital techniques. The part I liked about Agilent is that they are generous about making users of their products happy in general, regardless of whether you recently paid them or not. For deeply discontinued products (like 3+ generations ago), they are happy to pass whatever information they have left to help DIY-ers or non-chartered 3rd parties that are willing to service them (like this one, which people are asking for recovery discs for their 1680 series analyzer and the staff went all the way to dig up their private stash!) so the company can focus on the newer products.

Support culture aside, Tek’s used gears are so problematic (I learned it first-hand, the hard way) that I’m now hesitant about buying them as investments. It looked like an opportunity because Tek stuff often breaks the same way, so I can buy them cheap, fix them, and resell. But the reality is that the labor is simply not worth it. Now I’m just selling whatever Tek leftovers I have strengthened in the past.

You might think Agilent is sabotaging their own market by taking care of users of their old gears. It isn’t. Whoever that has the budget to buy new will do so. Wobblers between buying new/old gears are not worth agonizing over. The ones who are familiar with the older gears will grow fond of the brand and the user interface/environment they are familiar with and will push their employers to buy Agilent when they get a chance to buy it new. I used to have a customer that I convinced them to get a used Agilent one instead of used Tek, and they ended up loving it so much that they bought a new one from Agilent for their second scope. What goes around, comes around.

I realized throughout the years is that whatever hobbyists do with the old gears and can only help the brand image and build a stronger user base. It’s the user base (engineer’s familiarly) that makes or breaks the deal on new gear purchase. I don’t think big companies that pays good money to buy new will switch to all Tek from Agilent all of a sudden when all engineers are comfortable with Agilent’s stuff, and vice versa.

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