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).


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 mentioned 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 www.humgar.com.


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 are often 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.

EDIT: It’s not just me bitching about how unresponsive the controls (especially the dials) are in their user interface. Dave Jones did a video review of MDO4000 and a bunch of people share the same frustration in the comments section. I thought they improved after TDS1002B (I stopped following their newer scopes), but I was wrong. Still the same poorly thought-out and laggy UI.

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 has 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 it up from 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 because it’s often not just one problem, but one quickly after another. 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.


Oscilloscope Probing – Bob Pease Show

Once in a while customers ask me about what probes do they need to go with their high bandwidth oscilloscopes.

Agilent already has application notes about how to probe properly at high frequencies to ensure what you see on the scope represents the reality faithfully, but they are a little dry. Bob Pease Show at National Semiconductor (now acquired by Texas Instruments) talked about it and it’s great infotainment due to Bob Pease’s character:

This show has significant product placement by Tektronix, but the information there applies equally (and fungibly) to all major name brands such as Agilent/HP/Keysight and Lecroy. They all live up to the specs advertised.

What I’ve learned from the video

  • No-name brand probes might not live up to the claimed specs. I wouldn’t trust a Chinese probe beyond 100Mhz (or even 60Mhz).
  • Shorten the ground leads as much as possible, especially high frequencies. Wires are inductors/antennas.
  • Do not use the poor-man’s differential probes (aka subtracting the channels on the scopes): the channels aren’t matched perfectly, the probes aren’t matched perfectly either.
  • Design for testing: plan your PCB so you can probe easily.
  • For digital designs, high bandwidth scope users care more about (time-domain) step response: rise-time, ringing, settling, than it’s frequency domain (I don’t have a fast pulse generator, this is why I test it with a RF generator to check the specs)
  • Active probes have less loading and attenuation. You can use passive probes if you have a large enough signal to burn.
  • Probe capacitance (loading) kills a fast circuit (by damping it down)
  • Don’t be happy because you see nice waveforms and nothing bad happens with a low bandwidth scope+probe: you are just failing the capture transients.


Quick setup guide for Agilent E2050A GPIB Gateway

For the convenience of my customers, I compiled a quickie setup guide so they don’t have the RTFM.

E2050A does not have DHCP. Most likely your network doesn’t have a ancient BOOTP server, so it means you are better off letting E2050A have a static IP address.

The big idea is that you’ll first need to talk to the E2050A, and the only way it can happen is that the computer talking to it has to be on the same subnet (and the corresponding IP address range). Doesn’t matter how you achieve it as long as you keep this in mind. Once you gained access to the router (telnet config screen), you can change the network setting of the E2050A to match whatever network you want to put it on later.

If you don’t know the E2050A’s network configuration, reset it to the default so you have a deterministic starting point and follow the instructions below:

  1. Reset the instrument to factory state by holding down CONFIG PRESET switch while applying power, because you want to know the IP address for sure so you can get into the instrument.
  2. The default static IP address is, under subnet mask
  3. Most likely your internal network is not 192.0.0.XXX, so you might want to use a computer with a network card (NIC) to talk to the device directly* (point-to-point) first so you can gain entry to the E2050A and change its network configuration.
  4. The NIC on the computer talking to the E2050A must be set to an IP address in the same subnet. This means only the last (rightmost) group of the NIC’s static IP address can be different. An example for the computer’s NIC static IP setting: with subnet
  5. Now you can talk to the E2050A directly by addressing If it’s a dedicated computer for an automation set and you don’t want it to talk to the rest of the network, you are done.

I made up Anything from to works. Thou shalt not use (for it is the network identifier) or (for it is the network broadcast address) or (as it conflicts with the E2050A’s IP).

Most likely you will want to put the E2050A on your home/business network for convenience, unless you want to eliminate network security issues. Then you’ll need to follow a few more steps:

  1. Telnet to the E2050A at to change its static IP address and subnet to fit your network. After saving and rebooting, you must address it with the new IP address you assigned (obviously!).
  2. Note that the default (SICL) interface name on the E2050A is “hpib”, which is different from E5810A’s default “gpib0”. Either change it on the E2050A (it’s called “hpib-name”) or enter the “hpib” for interface name on Agilent’s I/O suite.
  3. You can leave the rest of the settings alone in Agilent I/O suite if you want to simply talk (in its raw, instrument-specific GPIB commands) to the unit without using VISA or SICL layers (standardized syntax).

E2050A has the same software communication interface as E5810A, so you can just select E5810A as the remote interface for the E2050A and remember to enter the correct interface name as discussed above.

Note that E2050A does not work properly (won’t detect) on the redesigned Keysight-branded I/O Suite until version 2019. Please either use version 2019 and after OR the older Agilent branded I/O Suite.

I have E2050A as well as E5810A for sale. Please contact me from my business website (www.humgar.com) or my phone 949-682-8145.

* Unless you are using a very ancient computer, the NIC can auto-negotiate direct connection that you can simply use any regular old straight RJ-45 cable. If you have a really old computer, you’ll need a cross-over cable to do point-to-point ethernet.