RPL1116 (MSO1000Z) and PLA2216 (MSO5000) Active Logic Probe teardown

[dren.dk]

You can't have the ground plane on top, that's where your components live, so very little copper would be left at these densities.

The holes poked in the power planes for vias alone takes out a lot of copper, even with 0.4mm clearance, poking holes for components would make it useless.

You can't connect the heat spreading copper layer to GND, because the bottom pad of the LMH7322 is connected to VEE (-2.5V), but with LMH7324 it's unconnected AFAIR, so you could if you used that in stead.

In my layout I have GND on Layer 2 and -2.5 V on layer 3, so I expect to get much better heat spreading than the original.

The yellow in this screen shot is the GND pour, the -2.5V heat spreading leayer is under that, but it looks almost the same: https://gitlab.com/dren.dk/mso5k-la-pod/blob/master/pcb-complete-in-pcbnew.png

[2N3055]

SCSI cables are as thick as your thumb, stiff, not bendable, weigh a kilogram, and are pain.
Without being screwed in or locked , they will fall out from connector under it's own weight.
There is a reason why every manufacturer uses flat cables for this. And they are usually very soft and pliable ones.

It would make sense to make it compatible with used LA cables that are available on E-bay for older LA and MSO scopes.

Or just make a flat cable from scope to a small board on user side, that has some kind of transition to hooks, grabbers or whatever you want to use for DUT connection.

[Rerouter]

2N3055, care to give some example links,

Its easy to route for whatever connectors are needed, I'm thinking 0.635 / 0.25" pitch ribbon if its possible to the pods, 2x13 is a very nice option for the pods 8 channels with a good number of grounds, or 2x15 if you want every pair separated by a ground. (I personally am leaning towards 2x13, as the buffered differential logic should be the safest signals on the board from crosstalk.

[2N3055]

2N3055, care to give some example links,

Its easy to route for whatever connectors are needed, I'm thinking 0.635 / 0.25" pitch ribbon if its possible to the pods, 2x13 is a very nice option for the pods 8 channels with a good number of grounds, or 2x15 if you want every pair separated by a ground. (I personally am leaning towards 2x13, as the buffered differential logic should be the safest signals on the board from crosstalk.

Sure, for instance: https://www.ebay.com/itm/Agilent-HP-10089A-Logic-Woven-Cable-w-Flying-Leads-for-54622D-MSOX2000-MSOX3000/253907595253?_trksid=p2485497.m4902.l9144

With logic pod cables, most pain is on the user side. Many people buy original MSO cables because they  come with nice hooks or grabbers.

Terminating into a small PCB on user side, that has a breakout pins, would make it easy to just get 10 PCBs and keep them permanently connected to DUT. That would make switching scope from DUT to DUT easy, and connecting DUT even easier. You could solder to it, making PCB disposable. You just order 10 more.
Or you can connect PCB to grabbers of your choice (or just arduino style pin connectors) and connect normally.

[dren.dk]

Does anyone have a good idea for the scope connector?

I just measured my scope and the depth of the cavity from the front of the scope to the bottom of the connector is just under 15 mm and the front cavity wraps quite tightly around the connector, so I doubt a standard ribbon IDC connector will be able to fit in there.

I'm currently thinking that a 2x25 pin socket with wirewrap pins (or those reinforced long pins as used for pc104) could be a solution.
With the tall socket the board that it connects to would sit flush with the front of the scope and have a couple of SMD connectors for the cables that run to the 8 channel pods, it would probably have to shaped to fit with the contour of the scope, to provide keying, but with a nice black board that would not look all that silly, I think.

Another alternative would be to get a proper keyed connector such as this and edge mount it: https://uk.rs-online.com/web/p/pcb-sockets/6081437/ that way the pcb will be sticking out horizontally, but I can't find a connector that's supposed to be mounted like that.

[Rerouter]

Wasn't exactly what I was thinking, could you explain that detail in more detail. As if we can find a source for those grabbers, buy those and terminate them to a 9 pin 0.1" header?  meaning you could have many of those 9 pin plugs read to swap to and from the pods at will??

I should point out the PCB's we are routing are the 8 or 16 channel pods with the ECL comparitors, I can make them pretty small if needed, but they need to be close to the grabbers,
If dual loaded 4 layer was in the mix, then an 8 channel pod pcb with a 0.05" 2x13 header / 0.635mm ribbon to the scope could be shrunk all the way down to 25x30mm, Small is not that hard, But the comparitors are not the cheapest parts to say you want 10 sets, the looms should be.

The other thing with getting this small is finding a good enclosure. I've come across just that many times in the past

[Rerouter]

If you have the exact opening size, we could also shim the PCB a little to ensure the pivot is away from the connector,

Equally that would let us know what we can get away with.
I do feel it will have to be inline soldered, but 50 solder joints is quite a bit of strength, considering that a 1.6mm board has barely any gap,

the shorter we make the breakout PCB, the less torque it will experience, so perhaps we attack it that way, almost 0 length from the first plug to the other 2? 1 plug in, 2 plugs out.

[dren.dk]

Sorry I didn't think to measure the opening width and height, but from memory it was just about as tight as the inside of the connector.

BTW. I think our venerable NPN power tranny friend was talking about doing away with probes and in stead connecting the pod to a breakout board with a cheap connector that allows you to solder the breakout board into the DUT you're working on and leave it there when switching to another project.

If we wanted to make the probe breakout boards super cheap, then they use a PCIe card edge connector, though I'd be wary of having that connector directly in the pod as that would be somewhat of a dangerous leaver to have on the presumably short and fragile probe wires that are soldered directly to the DUT.

I doubt PCIe connectors come in IDC ribbon variants, but this looks nice: https://www.te.com/usa-en/product-5-1734857-1.html

[Rerouter]

Looking into the LMH7324, It doesn't look like its normally stocked, For a 4 layer single side loaded PCB its actually pretty easy to route, more comes down to can anyone even get those chips?

[dren.dk]

Huh?
According to octopart lots of places have stock:  https://octopart.com/search?q=LMH7324
Mouser certainly has them: https://www.mouser.dk/Search/Refine?Keyword=LMH7324

Am I missing something?

Oh some other nice things about the LMH7324 is:
* The belly pad is unconnected so it can be tied to the GND plane, which means that I would not need to dedicate a layer to -2.5V
* It doesn't have settable hysteresis, so those two resistors go away, the original hysteresis is about 10 mV and the fixed one of the LMH7324 is about 21-24 mV), I can't see it making any difference.
* It doesn't have the latch feature, so the bus to supply those two logic levels and the resistors to pull them up and down go away too.

[madmac]

Do we really need such cables?
I think Rigol knows what they are doing...
I thought the main goal was to get a working  equivalent good pod like the original but much more cheaper... Not 350€...

A low cost solution if you are happy just looking at 3V3 and 5V0 signals is to use a single ended to LVDS driver and an inline resistor to offer a bit of protection.
75LVDS387 for 16 ways (or 8 way 75LVDS389, or 4 way 75LVDS391. The trigger level would not be used. A low drop out regulator can supply the 3V3 rail from the 4V0 supply.
Not for high performance.

[joeyjoejoe]

Do we really need such cables?
I think Rigol knows what they are doing...
I thought the main goal was to get a working  equivalent good pod like the original but much more cheaper... Not 350€...

I agree with this.

What is the design goal here?

The nice part, if we are dealing with KiCad, is anyone can design as they wish With the open source schematic that has been published, it's now just a few hours of figuring out routing.

For me, it's the price point. Cost of BOM and board (2 layer) would be above anything else. After all, if we approach anywhere near the retail price, you can buy a supported, engineered product direct from Rigol.

Using a cable from DSO to probe lets the board grow in size. It also presents the least risk to the DSO from torque - accidents happen.

[dren.dk]

I've just measured the cavity the connector on the scope sits in and it's at least 11 mm high, so it's not a problem to fit a regular 50 pin 0.1" pitch IDC ribbon connector in there, if that's your thing.


I had another thought about connecting the pods to the converter board and it struck me that HDMI cables is available everywhere, really cheap, exists in a lot of lengths and there are very thin and flexible models available too.

HDMI has 4 shielded twisted pairs and a bunch of extra wires, so it's perfect for an 4 channel pod, which is the minimum you'd get with a single LMH7324

The overhead of having 4 pods does seem a bit over the top, but getting to use commonly available, cheap and robust cables would be super awesome.

[Rerouter]

Ok, so looks like Ribbon Cable Assemblies are not that expensive for the wiring to the Pods,

https://au.element14.com/samtec/ffsd-13-d-12-00-01-n/cable-assy-26p-idc-rcpt-rcpt-305mm/dp/2856836

Now that leaves 2 options for the breakout board,
1 - Find a cheap source for a 2x25 0.1" ribbon cable about 200mm long, and plug that into the breakout board
2 - make the breakout board plug in directly, but shim the shape so its supported. e.g. 3D printed housing.

[joeyjoejoe]

https://www.digikey.com/product-detail/en/assmann-wsw-components/H3DDH-5006G/H3DDH-5006G-ND/1218621

$2.60

I think this is best - minimize risk of damage to scope, logic analyzer pod, or both.

[dren.dk]

Yes, it's certainly hard to beat a pre-fab ribbon, just for my own benefit these are the options I see for the scope to-pod-connection:

0: 50 lead 0.1" IDC ribbon connector plug into the scope and run all the way to the 16 ch pod (that's what my already completed 16 ch pod does).

1: 50 lead 0.1" IDC ribbon connector plug into the scope, with a very short ribbon that plugs into the breakout board that allows two tighter (0.025" pitch) 26 lead ribbons to go to two 8 channel pods.

2: Straddle mount a 50 pin female connector on the edge of the breakout board so it can be plugged horizontally into the scope.

3: Use an elevated 50 pin connector to allow the breakout board to sit flush against the front of the scope.


0: Easy to source, not that cheap, but a bit unwieldy with that huge ribbon.
1: Easy to source, but it just feels wrong to have a dongle on the scope like that, it's not an Apple product after all.
2: Somewhat easy to source, could be very cheap if a proper straddle mount connector can be sourced, but a bit harder to do because it requires a collar/case around the board to support it against the fascia of the scope, otherwise it more closely matches Rigols solution.
3: Could be harder to find the exact part, but super compact, cheap and robust with zero risk of putting stress on the scope connector, the board should be designed to fit flush against the front of the scope to key the orientation and the same board could be used for the #1 solution if unable to source the connector.

Samtec makes the connector: ESQ-125-23-L-D: https://www.samtec.com/products/esq and it's in stock in at least a few places: https://octopart.com/search?q=ESQ-125-23-L-D
I like Mouser and though they don't have stock, the lead time is only 5 days, so it's not too bad.

Mpe also makes it, but it seems to be a custom part: 100-2-050-0-NFX-YS0-1844:
https://www.mpe-connector.de/index.php?lang=en&menu=16&id_product=1002&order_code=100-2-050-0-NTX-YS0-2324

[wulfman]

Well it can all be done, all 16 channels in 2.3"x2" of space using the 4 channel devices.
4 layers is mandatory

[dren.dk]

Looks nice, though I think you need some thermal vias to tie the bottom pad into some heat spreading zones.

[Rerouter]

wulfman, that is with 0403 passive isn't it? If you even hopped back to a more normal 2x25 0.1" header, that would only make your board a sliver wider, at 2.5" wide.

[madmac]

wulfman, that is with 0403 passive isn't it? If you even hopped back to a more normal 2x25 0.1" header, that would only make your board a sliver wider, at 2.5" wide.

Wulfman's layout is for the  RPL1116 Active Logic Probe 68 pin connector.

[wulfman]

Oh yeah no way finished with it loads more to do   yes thermal vias etc...  but its going well.
I finished the routing but not the entire design. I was tired last night 

is the pinout for the 5000 series the same as for the earlier scopes ? if not the small board that plugs into
the scope would be the only thing different from this board to any scopes.

[dren.dk]

No, the mso5k uses a 2x50 0.1" pitch header, the pinout can be seen on the first page of my schematic: https://gitlab.com/dren.dk/mso5k-la-pod

The deci-inch connector pretty much demands a converter board, IMHO.

[wulfman]

Ok thats the pinout i used on my converter board. I like the 68 pin connectors they use on SCSI III drives as they are easy to get
and reasonable. you can use the flat internal or round external and the diff pairs use twisted pair in the cable.
I still want to use the diff pair equal length routing but setup is not easy since i have never done it before in Orcad.

[Rerouter]

What might make things easier is you have control of the order of the channels. And you only have to length match input to output. Whether its trimmed on the single ended or differential you can match the skew.

[wulfman]

Well diff routing was not hard. here is adapter board to 68 pin cable.