LeCroy Probus reverse engineering

[ollopa]

There are a few panel-mount push-on male BNC connectors out there. 

https://www.aliexpress.com/item/RF-electrical-terminal-connector-BNC-Plug-panel-mount-Quick-Push-on-bulkhead-with-Solder-cup-connector/32443473110.html

https://www.aliexpress.com/item/5PCS-BNC-Panel-Mount-Plug-Quick-Push-on-with-Nut-and-Solder-Cup/32704864505.html

Obviously PCB mount would be preferred so I'm looking forward to hearing back from wingel.

[Mechatrommer]

yes i saw that deck mount quick bnc type connector sold in ebay, the price is a bit high for a china brand. and its less neater than the original, the ground connector is "loose" type i'm not sure it will be impedance controlled. that will be the last option.

[wingel]

> for non EU members, can you share the source?

sure, I just wanted to check with the supplier that i was allowed to post their product drawing in a public forum.

I found an edge mounted BNC connector from a Chinese company called "Eastron" (eastron.cn) on Alibaba:

https://www.alibaba.com/product-detail/RF-50ohms-ST-180-degree-edge_60634004992.html

When I contacted them it turns out that they also have a "push-on" variant of the connector without the coupling nut as in the attached picture.  Not too hard for them to do such a variant I guess, since all they have to do is to build a batch of the normal connector and not mount the coupling nut. And they are willing to sell just a handful of them since they still have a few in stock.

The Alibaba page shows a picture of a vector network analzyer (looks like a HP 8753E which goes up to 3GHz or 6GHz depending on options) so they should be able to check the impedance matching of the connectors they manufacture.  I'm hopeful that the connector will be of decent quality.

Please don't buy up all of their stocks though, I want to buy some first.

[wingel]

(Updated.  Darn, I can't spell when I have just woken up and should be on my way to work.)

Finding a decent pin header turns out to be much harder.   I haven't found any supplier with any angled connector with 0.03" pins.

If one could just find a straight pin with the proper rounded end and surface finish (a couple of micrometers of gold on nickel) one could probably 3D-print or mill a plastic support to put the pins in.  And then build something like the attached picture with a bulk-head push-on-BNC to SMA adapter that one can find on eBay for a few dollars.

Build a small PCB like that with an I2C EEPROM on it and you'd have something that fits nicely in the LeCroy scope with no risk of inserting the pin header in the wrong direction.

Do you know any decent manufacturer that have an automatic lathe who could manufacture a run of a hunded pins or so and then plate them with nickel and gold?  It shouldn't be that hard to do, I just have no idea where to find a manufacturer who can do it for a decent price.

[Mechatrommer]

Please don't buy up all of their stocks though, I want to buy some first.

dont worry, alibaba is a bit inconvenient for me (not sure how to make order (and paypal payment possible?) and look at seller rating) and i'm not in great need, otherwise we still have alternative the china nutted version above. if you want you can buy all and post in ebay for non-EU member as well. the alibaba link you provided has the outer rotating/lock ring, lecroy doesnt. but i'm thinking we can improvise that by removing the outer ring using brute force or something hard. i thought i've linked earlier the pcb side mount of a BNC connector with lock ring. i measure it about 15.5mm tip to pcb edge. i have this a few in stock.

One more thing.  Could someone who has a LeCroy probe measure the pin header and post the exact dimensions.  I'm trying to find a supplier who can manufacture the connectors just to see how much it would cost, and it would be nice to be able to give them some drawings of the part.

not entirely sure what you want, but measuring with my rusty caliper on AP020, the internal of protruding rectangular plastic protecting/guiding the pins is 6.7 W x 5.3 H x 5 D (mm) the pin diameter is about 0.76mm type, the mill-max also have 0.46mm diameter pins like what i bought from china no brand ebay here, which is too loose and not suitable. the linked pogo spring loaded in 1.07mm dia i dont think that will fit. i browsed mill-max catalog i cant find 2mm pitch headers with 0.76mm pin diameter, 0.76mm pin only available in 2.54mm pitch format, so maybe need to improvise again

[Someone]

not entirely sure what you want, but measuring with my rusty caliper on AP020, the internal of protruding rectangular plastic protecting/guiding the pins is 6.7 W x 5.3 H x 5 D (mm) the pin diameter is about 0.76mm type, the mill-max also have 0.46mm diameter pins like what i bought from china no brand ebay here, which is too loose and not suitable. the linked pogo spring loaded in 1.07mm dia i dont think that will fit. i browsed mill-max catalog i cant find 2mm pitch headers with 0.76mm pin diameter, 0.76mm pin only available in 2.54mm pitch format, so maybe need to improvise again

You should be able to assemble a suitable pin array from mil-max 3150-2-00-15-00-00-08-0 or 3330-2-00-15-00-00-03-0. A PCB structure is robust enough to support and align an active interface as in here: https://www.eevblog.com/forum/projects/diy-100mhz-differential-probe/

[wingel]

Mill-max 3330-2 looks like it could work.  Thanks!

[ollopa]

Somewhat related thread on DIY probe construction for the older scopes, epoxy putty based ProBus connector, a couple more EEPROM dumps:  https://www.eevblog.com/forum/testgear/lecroy-pp092-2gssec-adapter/25/

[sixtimesseven]

Mill-max 3330-2 looks like it could work.  Thanks!

Did they work out in the end?

[MilkmanCDN]

Folks,

Many of the plastic tabs seem to be broken off on my older active probes.   I an effort to solve this problem, I took some calipers and created a 3D model.   .STL attached in the .ZIP file. 

To test fit the model, I printed on a FDM (Prusa MK3S) using Prusament Galaxy Black PLA filament.   The results were much better than I expected.   The fit is wonderful and after mounting it to an existing probe chassis, it feels like brand new.   Tight fit.   

Side-note: the back-side of the original connector appears to be covered in some kind of metallic paint.   I've found a few options, but haven't tested any of them yet.

I suspect printing on an SLA would produce better results, but alas, I don't have one (yet..).    If some one does, would it be possible for you to print and post pictures?

[MilkmanCDN]

Folks,

I believe someone was asking for 3D models of these two parts.    Pictures and Models attached.

If anyone finds a place to source these, I'm all ears.    I've been looking for quite some time but have always come up empty.

[dmderev]

Hello, could you please tell what is the marking on the chip located near R23 and R25 in the picture showing location of green jumper in your post. Most likely it should be a DAC? Which probe model this picture is from? Did you ever reverse engineered schematics?

[ollopa]

Hello, could you please tell what is the marking on the chip located near R23 and R25 in the picture showing location of green jumper in your post. Most likely it should be a DAC? Which probe model this picture is from? Did you ever reverse engineered schematics?

This is the probe AP022.  No, I did not ever try to reverse the schematics.

74HCT573C Octal D type latch
Q1 looks like a 5V regulator


But on the other side is your DAC: DAK703KU 16-bit monolithic DAC

[2N3055]

HCT573 is transparent octal D latch, PCF8574 is I2C 8 bit I/O expander.  With those 3, you  can clock in 16 bits for D/A converter (DAC703 16 bit voltage mode D/A with built in reference) to set offset with the help of LT1112 dual opamp....

[dmderev]

For those interested, here is how control of the input mode and offset is performed:

( I programmed the EEPROM for AP020 and used a preprocessor that acknowledges all transactions. )
1. The quality of the contacts in the connector matters, poor contact leads to a transition to strange modes (a red bar “Processing ...” appears. When I realized this, the work became predictable. EEPROM address - 50h (all address inputs must be at zero)

2. The binary images on the Internet contain only the valid data. The default programmer leaves FF in an unused area. It confuses the firmware. All free memory must be filled with zeros.

3. The oscilloscope reads entire EEPROM sequentially, regardless of the size of the data block, in one pass. Then it recognizes the probe, and switches the input mode (in my case, DC coupling is turned on and 50 ohms is not turned on - perhaps the resistor in the probe, although in the picture you can see only the place for its installation.

4. When you rotate the offset knob, the oscilloscope sends the following commands to two PCF8574 port expanders - at addresses 0x23 (data port) and 0x21 (command port). First, the most significant byte of the offset is written to the data port (for positive numbers, the most significant bit = 1, for negative numbers = 0). Then bit 0x01 is set in the command port (latch new data in 74573), after that the bit is cleared (data remains in 74573) and then the low byte is written to the data port. Perhaps this leads to a small glitch at the DAC output, but they are OK with it.

5. If these transactions are not acknowledged, the oscilloscope makes 4-6 recording attempts and stops.

6. For example, 0x8000 = offset = 0, 0x7FFE = offset = -2mV, 0x8002 = offset = + 2mV. In this case, the DAC code is likely to scale, since for the sequence 1,2,3,4,5,6mV codes 0x8002,0x8004,0x8006, 0x8007, 0x8009, 0x800A. But I am not 100% positive in scaling.

7. When switching the vertical scale and if the offset is not zero, the oscilloscope sends the correspondingly changed offset - that is, on the 1mV range, the 10mV offset will be replaced by 50mV when switching to 5mV. If offset was zero, the transaction is not done as it stays zero.

8. Depending on the input mode, the command port bits have the following meaning - 0x10 - when set, the DC coupled input. 0x40 = when set, the input is AC coupled (on probes, is this?) When both bits are cleared, the input must be Grounded. That is, switching the mode and writing a new offset corresponds to 0x23 = MSB, 0x21 = 0x11, 0x21 = 0x10, 0x23 = LSB for DC coupled, 0x23 = MSB, 0x21 = 0x01, 0x21 = 0x00, 0x23 = LSB for GROUND, 0x23 = MSB, 0x21 = 0x41, 0x21 = 0x40, 0x23 = LSB for AC coupled. The relay may be switching Ground.

9. I did not find the purpose of the remaining bits in the control port, other buttons and knobs do not affect the samples.

The schematic which illustrates the concept of control in case of AP020,AP022. The DAC appears in complementary offset binary.

Other bit settings may appear needed for other probes. It looks that WavePro recognizes newer probes (ZDxxx, ZSxxx) and lists their names, but does not send offset data to probes on I2C. Newer scopes should be able to do that.

[MilkmanCDN]

I've been tinkering away a little bit with the calipers as I believe someone asked for dimensions of the 6-pin probe connector.  I've attached a drawing which should give all the details one might need.   

Also included is an updated .STEP (AP214) model to allow input into popular CAD programs.

Again, if someone knows where to source these, I'm all ears.

[dmderev]

For those interested, here is how I solved the problem of round pins on 6-pin 2mm connector.
There is a Mill-Max part number 3330-2-00-15-00-00-03-0 (Mouser part 575-3330200150000030) - and also Mill-Max 3330-1-00-15-00-00-03-0. These are bulk round pins, gold plated. I made a spacer from 3mm thick FR4, and plugged these pins into a right-angle PCB dual-row 2mm header.

I cut a piece of 3 positions from the 40 pin header. Since the pins are thicker than regular 0.5mm pins of such header, one need to push them in rather strong. Once the pins are in the connector, I applied epoxy and pushed in additional FR4 spacer. This creates a nice angle connector which reliably plugs into the probe socket.

When combined with the 3D-printed shell, this allows to build the probe PCB that fits. The picture shows two connectors: angle one to put on PCB, and a straight one which I used for connecting to logic analyzer.

On the side note: I printed the shell from PETG filament. Because the walls are thin, they may split. Applying acrylic solvent cement (dichloromethane or dichlorethane?) "welds" and bonds the shell layers and makes it strong enough to latch on the probe connector.