Is there a modern replacement for the HO3508 LA probe? - Page 1
Forum section: electronics / testgear

author: RAPo
author_rank: Super Contributor
timestamp: August 26, 2023, 08:31:34 am
content: I got a very cheap Hameg HMO1024 oscilloscope, new in the box. Unlocked all the options.Now searching for the accompanying HMO3508 LA probe that is discontinued.Is there a modern replacement or a schematic?

author: RAPo
author_rank: Super Contributor
timestamp: August 26, 2023, 02:10:55 pm
content: Thanks for your answer, but oh man the price of the ZL03 could get a new scope for that ;-).

author: DRG-fan
author_rank: Newbie
timestamp: January 16, 2024, 12:38:33 pm
content: May I ask - how did you get everything unlocked? Please hint me - i have one similar unit coming in of R&S. Tks a million!

author: RAPo
author_rank: Super Contributor
timestamp: January 16, 2024, 03:42:47 pm
content: Seehttps://www.eevblog.com/forum/testgear/hameg-rs-hmo-scope-licenses-not-available-anymore/75/

author: TurboTom
author_rank: Super Contributor
timestamp: April 04, 2025, 02:51:57 pm
content: Since I got into possession of an HMO2024 by a fortunate coincidence (slightly defective unit donated by a friend...), I immediately became interested in possibilities to DIY a logic probe set. I found awebsiteof an individual (maybe a member here?) who already put considerable effort into reverse engineering such a unit from sources publicly available on the web (basically Dave's teardown video and photos). Unfortunately, it appears that he lost interest about one and a half year ago.I had a closer look at the way the communication between the scope and the pod is supposed to work:The interface at the oscilloscope is activated by pulling the "COM" line low via a resistor (which happens when the pod is plugged in). The oscilloscope will then activate the pod's 5V power supply on the paralleled pins 4 and 7. After a pause of 1.484s to allow the Zilog MCU to initialize, the scope sends 4 bytes of inverse level UART data (19200, N, 8, 1) to the pod (data sequence is 0x83, 0x02, 0x00, 0x01 if I got the polarity right) and waits for 18.5ms for the pod to reply. If it doesn't, the scope toggles the power supply line and restarts the sequence.I attached the schematic of the COM line interface of the digital pod and a scope screenshot of the data sequence the scope sends to the pod.In order to figure out what the MCU is required to answer, we would need a data log of a complete initialization of an original HO3508 or RT-ZL03 pod, preferably on both RxD and TxD lines inside the pod. So if someone's got an HMO scope with such a pod and would be willing to log this data, the information would be highly appreciated!Cheers and all the best,Thomas

author: RAPo
author_rank: Super Contributor
timestamp: April 04, 2025, 03:18:58 pm
content: Thanks, Thomas,I hope your (and mine) wish can be fulfilled.

author: Kean
author_rank: Unknown
timestamp: April 04, 2025, 05:54:55 pm
content: Here is a Saleae capture of the COM pin on my RT-ZL03 as I enable the logic channels on my RTB2000Channel 0 is pin 7 (power) and Channel 1 is pin 26 (COM)Screenshot shows overall timing, and the CSV has the data bytes and precise timingThe zip file contains the CSV data and Saleae capture if you want to view it in that software

author: Fenstergucker
author_rank: Regular Contributor
timestamp: April 04, 2025, 06:00:53 pm
content: Here is a recording from my RTB2000 with RT-ZL03. Unfortunately you cannot trigger when activating the logic probe. The oscilloscope is not working properly at this moment. Here is some data, maybe it will help.Edit: RT-ZL03 serial nr.: 1333.0715.02-105904-XgPeter

author: Kean
author_rank: Unknown
timestamp: April 04, 2025, 06:15:11 pm
content: Quote from: Fenstergucker on April 04, 2025, 06:00:53 pmNice! I decided not to use the scope to probe itself... it felt... wrong...Having your data as well as mine might help identify what is different in the data, such as serial numbers. My RT-ZL03 is 1333.0715.02-104189-QA.And because you captured the individual RX & TX signals, it is easier to see which end is sending. Because it is half duplex, all the transmissions by the Z8 mcu also show up as received data.

author: TurboTom
author_rank: Super Contributor
timestamp: April 04, 2025, 11:25:14 pm
content: Thanks a lot for perfoming these tests. I just composed a sequence that most likely resembles the actual initialization of the digital interface pod, attached as a PDF. It seems like for some of the inquiries, a scheme could be applied (i.e. every 4-byte inquiry starting with "8" as the most significant nibble gets returned identically except the high nibble is "0"). Lines 9 and 10 seem to identify the pod while lines 13~42 appear to transfer some calibration data from the pod to the scope, yet I don't know what that should affect.I may try rigging up a microcontroller on a breadboard and attempt to emulate this communication sequence. With a little bit of luck, this should activate the logic interface, then we can attempt to set up an inexpensive DIY logic pod, maybe without "proper" (timing?) calibration, but good enough for most DIY stuff.Cheers,Thomas

author: TurboTom
author_rank: Super Contributor
timestamp: April 07, 2025, 01:20:26 am
content: I'm very happy to report some success...I implemented all the communication that Peter reported in a small PIC12F1840 microcontroller (simply since there was one of those plugged in my breadboard in the "storage corner"). I arranged the interface as shown above with the NPN and PNP "digital transistors". After some debugging (basically getting the oscillator configuration and the baud rate right), I was able to test it with my HMO2024. It actually worked right out of the box, amazingly the communication on this scope seems to be limited to four bytes in each direction, and when turning off, another message gets exchanged, differing by only one byte... I guess this gets used to activate/deactivate the comparator supply. I wouldn't have needed to include all the messages / calibration data, but maybe this project may be useful for others as well who may need it. I attached some photos/scope screen shots of the messIf you zoom in on the HMO2024 screen, you may notice a few noise spikes on the data lines that indicate that the logic analyzer is actually working. I used the bright green LED to emulate a 3V zener to generate the PIC supply voltage -- in the original PODs, they seem to use a "real" zener for this job. The tiny, dim red LED indicates that the "power enable" line to the converters (none installed so far) has been set.I'll definitely step-by-step design such a DIY "DigiPod", but it may still take some time since I'm running low on spare time... Anyway, the highest hurdle has been taken, what remains is just diligence!Cheers,Thomas

author: Kean
author_rank: Unknown
timestamp: April 07, 2025, 01:43:28 am
content: Congrats!

author: Fenstergucker
author_rank: Regular Contributor
timestamp: April 07, 2025, 04:14:32 am
content: I still have old photos of the HO-2010 logic pod from my sold HM2008 CombiScope. Perhaps you can find some inspiration from the simpler design.Peter

author: Fieroluke
author_rank: Contributor
timestamp: April 20, 2025, 03:15:05 pm
content: HiI started the same project but from the other end. I reverse engineered the schematics from the video and the hacking page mentioned in this thread as well as the datasheets. I also looked at the HO2010 4 channel predecessor, interesting to see the evolution. My picture shows my layout efforts from about a week ago. I’ll share more when I‘m back at my desk.Some notes:- when making a replacement it‘s important where to get the leads. The R&S leads are unavailable as replacement parts! They do contain half of the voltage divider though as well as a cap, so this is important! The HMO operates with a 1:5 divider network using an 80k resistor (and a cap) built into the probe lead and the 20k in the pod. HP makes these leads with built-in cap and 90.9k resistor, to work with a 9.1k in the pod. Both have 100k input impedance, but HP ends up with a 1:10 divider. I need to divide Vthreshold by two to compensate. The layout supports both probes BTW.- There is little space for the processor, so I also used an 8 pin SO8 version with UART, but from NXP, mainly because I have a dev system and am familiar with it.- the original HO3508 only seems to switch the 3V power to the comparators using the Z8 and use it as a kind of dongle and to tell it apart from its successors.- FWIW the R&S ZL-03 successor uses a Z8 variant with more oomph and a separate 12 bit A/D converter IC. It‘s unclear what else it does, but it generates at least two Threshold voltages from the Vthreshold set by the scope. This way the probe can set separate thresholds for D0-D3 and D4-D7. And it can possible set 4 different hystereses.More after the holidays…

author: Fieroluke
author_rank: Contributor
timestamp: April 21, 2025, 07:30:10 pm
content: Interesting stuff! My interpretation is this…Looks like each message starts with a 1 byte message ID, followed by the length byte until the end of message. The message ID itself consists of a read/write flag (bit 7) followed by the item (variable) ID. Strange there is no checksum byte. All communication is initiated by the scope.Writing 83 02 00 01 means: write item 03 (power ctrl), 2 bytes follow: value 0x0001The pod then acknowledges with item id and echoes the value it actually wrote to the variable.If the length byte of a read is zero, the item is not an item array.Writing 01 00 means „read item 1“, no array. Response is 01 04 (item id, 4 bytes follow), 0x0001 0x0000 (version number V1.0?)Or 18 00 means read item 0x18, not an item array, response is 18 14 52… means item 0x18, 20 bytes item value follow, followed by 20 ASCII characters ID string16 02 00 03 means read item 0x16, array index 3.Respomse is 16 14 00 03 followed by 18 bytes: item 0x16, 20 more bytes in message, item array index is 3, item value are the next 18 bytes.Items/variables are:01 (r) (32 bit) version number? 01.0002 (r) (16 bit) ? 103 (w) (16 bit) power ctrl 0/104 (w) (16 bit) ? 1605 (w) (16 bit) ? 1606 (w) (16 bit) ? 1207 (w) (16 bit) ? 1408 (w) (16 bit) ? 1409 (w) (16 bit) ? 160A (w) (16 bit) ? 140B (w) (16 bit) ? 1416 (r) [0..0x13] (18 bytes) ?18 (r) (20 bytes) ID string, zero terminated19 (r) (32 bit) ? 11A (r) (16 bit) ? -111B (r) (16 bit) ? 3Comments?

author: codepainters
author_rank: Newbie
timestamp: April 22, 2025, 02:55:41 pm
content: Hi!Quote from: TurboTom on April 04, 2025, 02:51:57 pmI'm the author of the linked page - slightly late to the partyFieroluke (he's also here) pointed me to this thread.It's not that I entirely lost the interest, no no! It's just, well, life circumstances (kids, daily job, the usual stuff) that significantly reduced my spare time.And also...Quote from: TurboTom on April 04, 2025, 02:51:57 pm...I failed to discover this detail, despite trying various things (I'm pretty sure I tried pulling COM up and down, so I might have just overlooked something or done something stupid, I'll never know). It seems all my intuition so far was correct (COM pin, pins 4 and 7 for Vcc, scope as communication master, etc.), but I couldn't get any further at that time. After a few failed attempts my self-confidence and motivation were severely damaged. Hopefully my HMO1202 is still intactIn the meantime I bought HO2010 on eBay. While interesting in its own right (I'll probably write a teardown post), it's not much help in this case.Quote from: TurboTom on April 04, 2025, 02:51:57 pmThat is all very interesting.Anyway, I'm very happy to see that my effort has found a decent continuation. I'd be happy to help in any way I can - testing, etc.

author: codepainters
author_rank: Newbie
timestamp: April 23, 2025, 06:21:42 am
content: Quote from: TurboTom on April 04, 2025, 02:51:57 pmDid you find it by reverse engineering the pod PCB? As stated previously, I failed to get past this step.

author: Fieroluke
author_rank: Contributor
timestamp: June 13, 2025, 09:55:14 am
content: Circuit boards have arrived: the adventure begins…

author: petemate
author_rank: Regular Contributor
timestamp: June 13, 2025, 08:13:24 pm
content: Hi, just stumbled across this topic by coincidence. Also, by coincidence, I sold two HO3508 probes a few months ago. I took some photos of the internals prior to selling(I may have more that I didn't post). You can see them here:https://www.eevblog.com/forum/buysellwanted/fs(eudk)-rohde-schwarz-ho3516-logic-probesThe buyer did confirm that they work with his RTB2004 scope.

author: Ryzzen
author_rank: Newbie
timestamp: July 16, 2025, 05:17:32 pm
content: I recently got an HMO 3002, and I am also super interested in how your experiments turns out, keep us updated if you got any further. Do not hesitate to open a github project for it either if you want to share and get some help :p

author: Fieroluke
author_rank: Contributor
timestamp: July 17, 2025, 06:44:16 am
content: I‘m in the middle of building it. I have to assemble under the microscope so this is not for the faint of heart. The progress blog is at groups.io in the Hameg group, but I’ll also post here occasionally. Like today. 5V supply is working, next up are microprocessor and serial scope interface.

author: Ryzzen
author_rank: Newbie
timestamp: July 23, 2025, 07:41:42 pm
content: Soldering everything by hand is going to take some patience indeed, I usualy order the stencil along side the PCB in cases like that, so that I can hot air everything at once with solder paste, well worth the time gain

author: TurboTom
author_rank: Super Contributor
timestamp: July 23, 2025, 10:35:14 pm
content: @Fieroluke -it appears you copied the input layout of the original HO3508 PCB. The probe leads that come with this unit contain additional passives in their moldings and are possibly distributed-impedance wires, very difficalt to DIY replicate.Hence, in my unfinished attempt of a DIY module, I went to copy the HO-2010 frontend as shown by Peter a few posts above. This older unit appears to use plain wires as probes -- not as good reflection- and signal-fidelity-wise, but probably still good enough and much easier to DIY. Unfortunately, there are some unmarked resistors in that design, so here only common sense and maybe some expeimenting may help...Currently, the lack of spare time doesn't permit me to continue with the project, so if you succeed, I may just take the easy road and build a copy of your design. Fingers crossed!Cheers and all the best,Thomas

author: Fenstergucker
author_rank: Regular Contributor
timestamp: July 24, 2025, 04:02:21 am
content: Quote from: TurboTom on July 23, 2025, 10:35:14 pmHallo Thomas,I omitted the second part of the HO-2010 logic probe, which is in the oscilloscope. Here are two old photos, I don't have any better ones.Peter

author: Fieroluke
author_rank: Contributor
timestamp: July 24, 2025, 09:06:10 am
content: I totally agree, and I have a hot air oven and everything. But.I want to install components group by group and debug as I go. I skipped the breadboard stage, the Chinese PCBs are cheap enough.If everything is installed and I find a stupid bug in the power supply, I pretty much lose $100 worth of parts, because let's face it, I'm not going to harvest dozens of 0603 and smaller components and transfer them to a new board.Already found the first minor layout issue, no biggie, still. Then it's on to the -5V and 3V3 supplies, and finally one channel and do a test run. If I fry anything, I'd fry D7 of 8 lines and still end up with working D0-D6, provided I only populated the ECL circuitry for one channel.

author: Fieroluke
author_rank: Contributor
timestamp: July 24, 2025, 09:24:11 am
content: HI Thomas,thanks for your input and invaluable research regarding the protocol.Yes, the input stage took me the longest to reverse engineer, the rest was just datasheet implementations with a few component value variations.The probe wires are not available from R&S, not even for the new probes. My requests remained unanswered. Their customer service is abysmal, just downloading a PDF requires a registration process that prevents mortals with non-big-company domains from registering. They prefer selling new equipment, along with the wires. If a wire breaks, go and buy a new scope. Wonderful. But I digress.HP is much more open regarding this, you can purchase these probe leads on ebay real cheap, they look identical to the ones from R&S, so they probably come from the same sweat shop in Bangladesh or the Hunan or Guangdong provinces. I was unable to find a manufacturer in China, so getting HP is the best option.But - searching for probe wires same as when searching for a mate - it's the inner values that count, and here R&S and HP are different! The chubby part of the probe wire contains a voltage divider including a cap, which determines the input impedance, and here HP uses slightly different values. I think 1:10 vs. 1:9 or something like that. The cap in the probe wire and the corresponding cap in the probe must correlate with the R dividers because using only Rs would result in a divider that's good for DC, but not high frequencies. HP is very open regarding these probe wires, they even include component values to use when including the dividers on the target PCB using debug headers. Way to go HP!Luckily the whole thought train and calculations were described very well in some application note I found at R&S, so I was able to calculate the correct component values when using HP probe wires instead of R&S wires.Bottomline: please be patient, when it's all working I'll publish it. Maybe it makes sense to design a tiny flex pcb for just the probe lead divider that you can embed into a small case while 3D printing it (you know, print, pause, put pcb in half-printed case smooth side up, put some goo on smooth flex and continue printing.)

author: Fieroluke
author_rank: Contributor
timestamp: July 25, 2025, 10:25:08 am
content: If anyone is interested, page 9 shows details of the Agilent/HP probe tips:https://xdevs.com/doc/HP_Agilent_Keysight/agilentprobing.pdfThe HP has a 90.9k resistor with likely 9.1K inside the LA (pod in our case), resulting in 100k total, 9.1/100 attenuation.At low frequencies, the attenuation of the probe is determined by the resistors. At high frequencies, the capacitors become dominant. Then the attenuation of the probe/pod combo depends on the ratio of the capacitors. The capacitance of the pod input capacitor must be selected to form a 100:9.1 voltage divider with the cap in the probe wire. Then the divider works across all frequencies (up to a limit of course). Same as a scope probe btw.

author: Fieroluke
author_rank: Contributor
timestamp: July 26, 2025, 06:18:23 am
content: The part number of the probe leads I’m using is 5959-9333 (pack of 5).Specs can be readily found.

author: Fieroluke
author_rank: Contributor
timestamp: August 04, 2025, 06:09:12 pm
content: I have implemented a protocol handler emulating the entire protocol described in this thread, and I’m now able to turn the pod on and off using my HMO724. It should emulate the newer pod for newer scopes too.This is an older scope and it only supports very few messages.One message is particularly important, as it switches power on and off (all values hex):83 02 00 00 or 83 02 00 01I interpret this as Write Variable 3, 2 bytes follow, 16 bit value 0 or 1 for off/on.Scope expects the response03 02 00 01: Report(Read) Variable 3, 2 bytes follow and the value that was set.But when the pod is off, the scope sends83 03 02 00 01Again: Write Variable 3, 3(!) bytes follow.Values 02 00 01.The response 03 03 02 00 01 is accepted by the scope.Still, the two variants of the same message are strange.

author: Fieroluke
author_rank: Contributor
timestamp: August 13, 2025, 10:21:38 am
content: A brief update in case anyone is watching this space:- Positive and negative voltage converters are working as designed, 2.56V and -5.2V- I have calculated the threshold voltage divider for use with HP/Agilent leads, have yet to test it.- The hardware will work with either HP/Agilent or Hameg/R&S probe leads, but different resistors must be used/omitted so one has to choose.- I'm waiting for one (hopefully) final part to be delivered, once that's here, I can do final testing and hopefully publish everything.On a side note:The R&S ZL-03 isn't such a bad deal, even if it's pricey! The parts alone (ok, ordering from Mouser, but still) run about $75, plus the multilayer board ($25 with shipping). And you need to have fun soldering 0603 and smaller parts, have a steady hand if you use stencil/oven or better yet have the board populated. And purchasing the test leads isn't cheap either, I paid $25 for a pack of 5 (so $50 total), and the ground leads set you back about the same (another $25). Finally the little hooks/test clips, quality ones are also $5 a piece, which comes to another $50 with shipping.Grand total over $225, if I calculated correctly, and that's without an enclosure or assembly.So, not a lot of money saved, but a fantastic learning experience...

author: Fieroluke
author_rank: Contributor
timestamp: August 13, 2025, 10:24:53 pm
content: Minor setback.A few observations:The 4 comparators get warmer than I thought. But they’re ECL, so maybe that’s to be expected. I hope.More seriously, calibration of the pod fails (see image) The manual mentions very little what’s going on except the leads must be plugged in. Since the voltage divider is in those leads, that pulls the inputs to ground. Without leads they’d be floating. Manual says it’s calibrating input thresholds. With all inputs pulled to ground, the comparators will go 0->1 only when the threshold voltage goes negative, right? So maybe the scope steps through the threshold range noting when the inputs toggle. The Z8 also has an input labeled „ANA“, maybe it‘s measuring something? Threshold voltage at the pod maybe?Either way, the scope is looking for something and I’m missing something…

author: Fieroluke
author_rank: Contributor
timestamp: August 17, 2025, 10:53:54 pm
content: Success: self calibration runs through now!Turns out the scope doesn’t send any messages to the probe, it just searches for the threshold voltage for each channel during self calibration until it toggles. Seems part tolerances result in threshold variations. Maybe that’s why the ZL comes with a DAC: to be able to tweak heavy threshold individually…Did find and fix a small layout flaw though, so scrapping my remaining boards.I’ll make a final batch of the fixed version though, and I have yet to design an enclosure.

author: Fieroluke
author_rank: Contributor
timestamp: August 23, 2025, 02:54:32 pm
content: Happy to report development is now complete!I had to make a few minor changes to the layout, so my spare PCBs are going in the scap.My pod works with either Hameg/R&$ Probe lead$ or HP/Agilent leads, which are readily available and supposedly cheaper because they’re not hand crafted from pure unobtainium by naked virgin fairies in a magical forest in Narnia..Depending on which leads are to be used, different resistors/caps need to be used, and since the HP leads are longer, the enclosure must be fitted with a small spacer. But everything is still 3D printable. As a result, input impedance is 100k with the original leads and 113k with HP probe leads. Other than that, identical pod!I’m going to 3D print the final enclosure on Monday, stay tuned!

author: Fieroluke
author_rank: Contributor
timestamp: August 29, 2025, 03:15:05 pm
content: Finished designing an enclosure optimized for FDM printing.I’m very happy with the results…Now I have to make a nice sticker…