## RS-232 Stop Bits in Agilent Instruments

Turns out Agilent instruments do not use the same defaults for the RS-232 in their instruments.

54600 series uses 1 stop bits (most common):

However other bench instruments such as power supplies (E3640 series 663X series) and 33120A arbitrary waveform generator uses 2 stop bits (fixed regardless of parity), which is usually NOT THE DEFAULT for most terminal clients:

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## InfiniiMax AutoProbe 1 Caveats

For most mortal souls probing up to 12Ghz, Agilent’s integrated active probe system is called the the AutoProbe 1, which looks like this:

Regular full blown Windows-based Infiniium oscilloscopes takes any AutoProbe 1 probes (as long as the shape fits), but I noticed my DSO6104A (InfiniiVision 6000A series) do not take my 1152A (2.5Ghz) probes nor my fancy 1168A (10Ghz) and 1169A (12Ghz) probes.

Turns out the more compact, embedded (VxWorks) Agilent scopes that boots almost immediately. It’s called the InfiniiVision Series, which covers 1000 X-, 2000 X-, 3000A/T X-, 4000 X-, 6000 X-, 5000, 6000, and 7000 Series.

I’m not rich enough to get my hands on the X series, but I know from the architecture that 5000, 6000 and 7000 series are basically the same scope. 5000 and 6000 series looks almost identical while the 7000 series adds a giant screen and a slightly different keypad layout (the BNC ports do not align with the channel buttons and dials).

Turns out the datasheets shows two caveats:

• 100Mhz model uses different hardware. They don’t take Autoprobe interface as there’s absolutely no reason why you need an active probe to get 100Mhz single ended. Agilent skipped the hardware for it (thus the autoprobe pins) altogether although they kept the recessed space reserved for Autoprobe so they don’t have to mold a different front bezel just for the 100Mhz models.
• They basically take only Generation I AutoProbe I, namely the 1130 series
• Gen 0 (not an official name) AutoProbe 1 does not work: 1152A (2.5Ghz single ended) for 54845A. These differential probes: 1153A, 1154A, 1155A, 1159A are also considered too old. They were intended to work with old Infiniiums such as 54845A
• Gen 2 AutoProbe 1 (only 10Ghz 1168A/B and 12Ghz 1169A/B models) does not work. These embedded scopes usually max out at 1.5Ghz, with the exception that 6000X goes up to 6Ghz, which is still way below 10Ghz
• N2800 series are Autoprobe I, but it’s Gen III (has a bigger butt extending away from the AutoProbe I hole), so it doesn’t work
• The rest are Autoprobe II and III that’s beyond our mortal souls (and way out of the league of InfiniiVision scopes)

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## E5070B / E5071B shutting itself down immediately after turning on

Got a second customer coming in today with a E507XB series network analyzer that does not turn on. Looks like it’s a common problem within the model series.

If the unit turns on without the CMOS battery but it doesn’t turn on the 2nd time after the CMOS was cleared, you have a very expensive problem which likely I’m the only person who can solve it because it’s months of effort tracing the circuit and the timings inside. I regretted chasing down the rabbit hole and spent more labor than 3 good unit’s costs for the few grands I’ve charged, but I might be able to recoup the labor in the future as more of the E507XB fails the same way.

UNLESS it’s a SC815E (there are 2 revisions that uses different motherboard), it’s NOT the motherboard or the power supply. I’ve seen some faulty SC815E doing the same on other model series, but not the VP22s (I replaced 4~5 different VP22s, they all do the same thing). It’s some good timing issues that’s hard to pinpoint to a specific module (you can replace everything on the digital side and it still doesn’t work) which I had to design, build and test a special circuit to correct it.

If you have a unit E5060 series or E5070 series VNA (Vector Network Analyzer) that doesn’t boot, I’m likely to have the exact experience fixing it. Of course I’m open to solving other problems with the analyzer as well. I offer free eval (no fix, no fee). Please email me at owner@humgar.com or call me at 949-682-8145.

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## HP 54502A Datasheet typo about AC coupling

The cutoff frequency of 10Hz on the datasheet is a typo. Better scopes at the time claims 90Hz. 10Hz is just too good to be true.

Found the specs from the service manual:

Don’t be fooled by the -3dB cutoff and ignore how wide the transition band can be (depends on the filter type and the order). Turns out this model has a very primitive filter that AC couple mode still messes square waves below 3kHz up despite the specs says the -3dB is at 90Hz. You better have a 30+ fold guard band for old scopes!

Remember square wave pulse train in time domain is basically a sinc pulse centered at every impulse of the impulse train in frequency domain superimposed. Unless you have a tiny duty cycle (which is not the case for uniform square waves, they are 50%), the left hand side of the sinc function at 1kHz fundamental still have sub-1kHz components that can be truncated by the AC coupling (high pass filter).

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## HP 54003-61617 Probe = HP 10017A

I have a 54003-61617 probe lying around and I never got a chance to find out what bandwidth so I rarely used it. After some digging, thanks to searchable PDFs, I found on 1986-04 edition of HP Journal (Archived copy here) that 54003-61617 probe is equivalent to 10017A:

By the way I noticed HP Labs still had the old HP Journal PDF files hosted on the website except without indexing: https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/YYYY-MM.pdf, replace YYYY with year and MM with month.

HP Journal (hparchive.com has an excellent collection) is an excellent source of hard-core electronic engineering education materials, better than anything you can get in colleges because electronic circuit design (not IC designs) is not an academic research area anymore. As of 2000, the only way to get into this area is to work at companies (apprenticeships) instead of formal training like classes. There’s a little problem though because this specialty (analog electronics) is so disorganized, very often even veterans in analog electronics has blind spots like not taking advantage of math tools/thinking enough (they tend to be very good at back-of-envelope calculations).

Finding the specs for 10400A series (10017A) is not easy either because the datasheet is not on Keysight (the new name for HP’s instrument division). It’s listed in an 1998 catalog “How to Select A Probe” kindly hosted by Marc Mislanghe (who passed away in 2014) as HPMemoryProject.org that listed the specs of 10017A in attempt to find an approximate ‘modern’ substitute:

HP 10017A (54003-61617) mini-probe has the following specs:

• Attenuation: 10:1
• Input Capacitance: 8pF
• Input Resistance: 1MOhm
• Bandwidth: 300Mhz
• Compensation range: 9~14pF
• Takes up to 300V
• 1 meter long cable

Even older record, Operating Note Part No. 5955-6270 courtesy of HParchive.com shows:

I bought a bunch of snap-on ground lead alligator clips (MP2+MP3) and grabbers (MP7) for the probe

The snap-on alligator ground clip actually has two parts: the alligator clip (MP2, 5061-1258) and the snap-on ground lead (MP3, 10006-61301) and they are screw-mated :

I happened to have bought a pack of multiple new ground leads and grabbers (MP7, 10017-69501) for this model series, more than what I’d need. They’ll fit miniature probes models 10017A, 10018A, 10040A, 10041A, 10042A.

These accessories will also fit 10021A, 10022A, 10026A, (10027A?), 10032A, 10033A as well.

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## Demystifying comparisons between eBay managed payments and the old way Hint: it's still the old final value fees (before cap) + payment processing fees (analogous to Paypal)

Most often when we sell on eBay, we receive Paypal payments, so we ended up paying eBay’s commissions (also called the final value fee, FVF for short) and Paypal processing fees as a percentage of the sale.

Now eBay pushes out Managed Payments (MP) which combines payment processing fees with the eBay commissions (FVF) because eBay now manages the payment gateway. The rest is every time you sell something, you get a payout (sales – fees) deposited directly to your bank (it used to be collecting paypal balances then withdraw it).

They have a different calculation formula which they claimed the sellers are better off in most cases, but should we take eBay’s word for it? Regardless of whether you are enrolled in managed payments, the fee percentage for each sale depends on:

• eBay store subscription level
• category

It’s impractical to do the side by side fee structure comparison to see when we are better off for each sale, plus we cannot easily switch between the two plans.

It’d be very helpful if we can put the managed payment fee structure on the same form as the conventional eBay+Paypal fee structure, and figure out under what conditions we are better off or worse off with managed payments.

Initially I was ready to do the derivations to put both plans on the same scale, but I spotted that managed payment (combined) percentage is simply the vanilla (non-managed) eBay category final value fee + 2.35% payment processing fees! That’s how they’ve calculated the combined managed payments percentage!

This makes life a lot easier. Since I can factor out the 2.35% that applies to the whole sum (which also include shipping and sales tax) regardless of the fee cap, this works exactly the same as Paypal (which charges 2.9%) and we are getting a 0.55% discount in payment processing fees.

For managed payments, since we’ve already separated out the payment processing fees, the fee cap applies to the vanilla final value fee portion which is equivalent to the old eBay final value fee. Keep that in mind.

The part that has changed is the fee cap. The old way caps the commissions/FVF directly regardless of product category, yet the new way (managed payments) caps the sale price that are charged commissions. This means the fee cap goes up or down a little depending on the final value fee percentage class applying to your sale.

eBay set the (commissioned) sale price cap to closely match the realized commission cap in the old way, for example non-store subscriber who will have their raw final value fees capped at $750 will see the same cap for the most common 10% categories (12.35%-2.35% = 10%) because the (commissioned) sale price cap is$7500, which $7500*10%=$750.

Big industrial equipment also have the same cap regardless because $15,000*2% =$300.

For non-store subscribers, 10% is the anchor (iso-fee-cap) category. So you are a little worse of with books (price cap +2%) and better off with musical instruments (price cap -6.5%).

For store subscribers, you get a bit more break over the fee-cap (lower) because your final value fee percentage is lower than the anchor (likely they chose a breakeven point at 10% when determining the sales price to cap final value fee over. Just easy numbers, not rocket science):

 Managed Conventional Discount* Common (9.15%) $2,500*9.15% =$228.75 $350 (Small stores)$250 (Big stores) $121.25 (Small stores)$21.25 (Big stores) Heavy gears (1.5%) $15,000*1.5% =$225 $250$25 Books (12%) $2,500*12% =$300 $350 (Small stores)$250 (Big stores) $50 (Small stores) -$50 (Big stores worse off) Guitars (3.5%) $2,500*3.5% =$87.5 $350 (Small stores)$250 (Big stores) $262.5 (Small stores)$162.5 (Big stores)

I call Basic/Premium ‘small-stores’ and Anchor/Enterprise ‘big-stores’.

So here are the observations, which is all you need to know:

• Under managed payments, small-stores gets a better deal than big-stores, because the advantage of the $100 lower fee cap with big stores are eliminated with variable fee caps. • The breakeven line for small stores ($350 cap) is 14% fees ($350/$2500), which the highest category is 12% so far. This means small-stores are ALWAYS better off switching to managed payments.
• The breakeven line for big stores ($250 cap) is 10% fees ($250/$2500), which the only category above that right now is books (12%). Big-stores selling BOOKS are worse off with managed payments. So in other words, • everybody is better off with managed payments (fee-wise) EXCEPT big-stores selling books • under managed payments, there’s no final value fee advantage for being a big-store * Remember you got 0.55% discount over the payment processing portion of the fees too and is not shown here since we’re just talking about savings in vanilla final value fees. As far as books (12%) is concerned, if you are a big-store owner, your raw commissions cap raised from$250 to $300 because$300 = $2500 * 12%. But if you factor the 0.55% discount, if the sale price is$x,

Since the raw commissions stops at $300 ($2500 * 12%), the additional $50 cap increase starts to get offset (and turn out positive as the processing fee discounts outweighs the commissions cap increase) when the payment processing discounts ABOVE$2500 covers all of it:

So the range of sale price x which the only setup (books for big-store sellers) can do worse is

There are some ambiguities (technically incorrect documentation) on eBay’s website which implied vanilla final value fees (portion) are charged for sales tax. I made a sale and checked the numbers and it’s not true. Only the 2.35% payment processing fee portion is charged against the sales tax (like paypal for handling extra money), the category final value fee (in my case 9.15%) is not applied to the sales tax.

They actually meant “the 2.35% payment processing fee portion” when they said “managed payment final value fees”. This is also part of the reason why I wrote this article, because they do not use the language that conceptually separate the two portion of the combined final value fees (vanilla final value fee + payment processing fee) in managed payments, thinking that they are simplifying the math for sellers, without realizing if the two concepts really fused into one, they’ll be shortchanging sellers over sales tax.

The $0.3 fixed per-transaction fee applies to both managed payments and the conventional way (Paypal also charge +$0.3 fixed per-transaction), so nothing has changed.

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## FREE oscilloscopes for innovators in response to #ChinaVirus #CCPvirus

https://www.humgar.com/CCPvirus-Urgent-Innovation-Response/

In the time of national emergency against the Chinese Communist Party Virus, or #CCPvirus in short, we are glad to offer FREE basic 100Mhz oscilloscopes (or mixed-signal oscilloscopes) to makers and engineers in the US who are stepping up with innovations to help.

Example include:

• Simple ventilators that can be built quickly within US (https://www.agorize.com/en/challenges/code-life-challenge)
• Robots that reduce direct human interaction with the infected patients
• Machines that sanitize the contaminated environment quickly and efficiently
• Any innovation you can come up with to help the front-line medical staff, produce the medical supplies we need, improve the logistics, and means to slow the spread.

Just send me (to wonghoi@humgar.com)

• a project description
• why you need the oscilloscope
• whether you need the logic analyzer function (mixed-signal)
• does your project require fancy oscilloscope features like FFT, calculus, phase difference, deep memory, talking to the PC

and I’ll make the arrangements immediately.

Currently available models (subject to availability)

• HP 54645A
• HP 54645D
• Agilent 54622D (Mixed-Signal)
• HP 6632B Systems Power Supply (20V, 5A, Fast recovery)

These models has a no-brainer learning curve for any motivated maker/engineer who are up to the game innovating something serious. Time is ticking. We want you to use the oscilloscope right away! Higher bandwidth oscilloscopes are available as loaner if your project justifies it.

It’s on an honor system. Please don’t abuse the program so the innovators who genuinely need the oscilloscope will have what they need!

We thank all the innovators who contribute their time and effort in response to the CCP virus outbreak!

Stay safe, wash your hands, and stay home whenever practical.
Save lives by slowing the spread within our medical system’s capacity.

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## Stanford SRS PS350 High Voltage Power Supply Repair

I received two PS350 power supply units that one of it has sparks when output is enabled and the other just won’t output anything at all.

The only repair info I found is from one of my favorite youtube channel the Signal Path. However, his unit has a much easier problem: the solder joints cracked because PS350 uses the metal case as a shield that are subjected to mechanical stress.

However, after difficult troubleshooting, I realized one unit has a fried resistor in the HV section, and a few core MOSFETs shorted.

The other unit is much more difficult: not only the HV capacitor is blown, resistor is blown, diodes shorted (won’t be able to detect it by probing in-circuit because of the capacitor ladder), PCB trace to the feedback path vaporized (without that the voltage will rise uncontrollably until something’s fried), and a bunch of MOSFETs, transistors and regulators ICs needs to be replaced.

Likely both units are broken because the users switched polarity without turning the HV section off (and let the voltage bleed out). This is very important and the markings on the case already warned the user NOT to do so.

You absolutely must NOT change the polarity while the output is live because the components in the HV section are marked for 4~6kV, so there is little room for a voltage spike past the operating voltages. The act of switching out the polarity (by mechanically swapping the pins through the dial switch at the back) doubles the voltage stored in the capacitors in a voltage multiplier ladder, so you are almost sure to crack the HV capacitors and likely the HV diodes.

Since I’ve developed experience for repairing SRS PS350 by reverse engineering some of the circuit sections, I welcome request for repair evaluation (no fix, no fee). Please call me at 949-682-8145, or meet me at www.humgar.com.

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## A Positive Tektronix Customer Support Experience

I often have bad experience with Tektronix product’s design (user convenience, reliability and repairability issues), and the by policy poor support for discontinued products. So far I have yet to get a chance to say good things about Tektronix while Agilent blew them out of water in these 4 areas.

Nonetheless, I have something good to say about Tektronix today. I have a DPO4000 series oscilloscope that the knob and busing popped out during shipping and disappeared, so I had to order them from Tektronix.

The operator on the phone noticed the part numbers and was aware that it’s a common problem that the jog shuttle’s knob and busing (for the Wave Inspector feature) often come loose, and offered to send it to me for free. That’s excellent customer service. The part that I admired the most is that they proactively acknowledged their design weakness and make amends.

Seems like Tektronix takes good care of their customers as long as the models are still supported. Definitely a redeeming quality!

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