Looking for any HPAK schematic that utilizes 1NB4-5036 logic comparator

[Jwalling]

Apparently these were used on many scopes and logic analyzers including 54622D.
It's also on the 54830 series MSO versions and MSO8000A series scopes.
Working on an MSO8104A where D11 is stuck low. Probing at the connector in the scope shows that it's biased way too low (negative) when comparing to D12. It's probably this chip, but I'd like to see a typical schematic to be sure.

This is causing the scope to fail the "Common" part of the self calibration routine:

Code: [Select]

Setting Pod 1 Threshold -5.000000e-001                                               

    Pod 1 Activity : 0xf70008ff                                                     

   Low thresh for POD_2 < -500.00 mV                                                 

   ThreshNull[POD_2] = 230.0 mV                                                     

Pod 0 High: -60.000189mV, Low: -190.000206mV, Cal Val: -125.000194mV                 

Pod 1 High: -40.000193mV, Low: 500.000000mV, Cal Val: 229.999900mV                   

Logic Threshold Cal Failed                                                           

>>Time 9 Seconds                                                                     

Finished ---- LogicThreshCal ---- FAILED                     

[shakalnokturn]

Did you get anywhere with schematics? Any reliable source out there for this part number?

[Jwalling]

Did you get anywhere with schematics? Any reliable source out there for this part number?

Never found any schematics, but replacing the chip fixed it. Only one seller on Ebay has them now, though this is not the seller I purchased it from:
https://www.ebay.com/itm/363347800865?

[MarkL]

I don't have any schematics either, but here are some notes on the 1NB4-5036 pin usage from a 16717A logic analyzer card.  Read backwards in the thread for some scope traces and additional information on how the 1NB4-5036 is used in that circuit and likely others.

  https://www.eevblog.com/forum/testgear/agilent-16717a-comparator-and-zoomchipseltest-failures/msg3136484/#msg3136484

[shakalnokturn]

Thanks to both of you for your replies.

I had since seen that topic MarkL, thanks for sharing your findings.

I bought a 54622D a couple of days ago that turns out to have two buggered digital inputs, a pity because the scope is otherwise complete with accessories and in fantastic cosmetic condition. I'm having trouble deciding if I should return it to seller and if not, at what price it's worth keeping as-is.

Can either of you remember from which seller you bought the comparators if not pulled from a spare L.A. PCB?

Google leads to a seller on AliExpress that was tempting but seems out of stock.
As for above eBay link to seller "polida2008" it could be an option as much as a waste of time, money and temper. I've bought power transistors from them in the past that turned-out to be fakes...

Looking at MarkL's photo with 1NB4-5036 removed I don't quite get the stated pinout for pin 29 which looks like a comparator input not GND. These IC's seem to have 9 external inputs and one common (to DAC) input for threshold reference. In the 54622D would this leave one spare comparator that could be bodged to replace a dead comparator input? If 1NB4-5036 is no longer obtainable would a MAX9693 piggyback bodge be reasonable? Of course either of these solutions are going to be awkward if timing is critical...

On this MSO the dead channels will not toggle for any threshold setting when tested with probe comp. output and logic pod, they have a unloaded DC output of -2V for one and -200mV for the other with +/-10mV on good channels.
Would you agree that the most likely failure is comparator internal input protection diode defective due to having been hit with excessive negative voltage?
If such is the case is there any chance of fusing it away (lab PSU between input and negative supply rail) without killing the whole I.C?

[Jwalling]

The seller I bought it from: https://www.ebay.com/usr/nbhightech?

[MarkL]

Can either of you remember from which seller you bought the comparators if not pulled from a spare L.A. PCB?

I pulled my replacement 1NB4-5036's from a dead LA board.

Looking at MarkL's photo with 1NB4-5036 removed I don't quite get the stated pinout for pin 29 which looks like a comparator input not GND. These IC's seem to have 9 external inputs and one common (to DAC) input for threshold reference. In the 54622D would this leave one spare comparator that could be bodged to replace a dead comparator input? If 1NB4-5036 is no longer obtainable would a MAX9693 piggyback bodge be reasonable? Of course either of these solutions are going to be awkward if timing is critical...

You are quite right on pin 29.  It is an input.  And I was also wrong on the test clock signal level.  It's actually 50mV and not 5mV.  I should have realized 5mV is too small for a clock input as I was typing it in.  Embarrassingly, I already found these errors months ago and failed to post the corrections.  Very sorry about that.  I will post an update to that thread.

I like your idea of substituting an unused comparator section, but unfortunately it sounds like you need two.  So depending on where you have dead channels and working comparator sections, you may end up with jumpers between the two chips.  Don't let them get so long that they compromise high frequency performance.

I don't think the MAX9693 would work.  From the scope traces in the referenced thread, the 1NB4-5036 outputs are >0V, and the MAX9693 has an ECL output (<0V).  Maybe the 54622D biases the output differently.  The MAX9693 may also have different delay characteristics which could cause skew problems with fast clock inputs.  Plus the self-test, assuming the 54622D does it in a similar way to the LA cards, is going to fail.

On this MSO the dead channels will not toggle for any threshold setting when tested with probe comp. output and logic pod, they have a unloaded DC output of -2V for one and -200mV for the other with +/-10mV on good channels.
Would you agree that the most likely failure is comparator internal input protection diode defective due to having been hit with excessive negative voltage?
If such is the case is there any chance of fusing it away (lab PSU between input and negative supply rail) without killing the whole I.C?

It could be the input diodes.  As I recall, the logic analyzer cards are fairly well protected before the signal gets to the comparator.  I suppose someone could have put some high voltage signals directly into the connector (DIY probes, or whatever).

What is the swing on the good inputs and outputs?

If the seller is allowing you to dig in a little, you could try lifting the input and output legs on the bad channels and try your substitution idea above.  I have little doubt that you can get your hands on a 1NB4-5036 either now or when more become available, but if there is a problem with the digital acquisition input, that is going to be a bigger problem to repair.  So, if you really like the scope, the idea is to make sure the acquisition input is ok.

I would not bother to try to fix it by trying to blow the dead protection diodes.  You could blow up more than you wanted and kill the whole chip.

[MarkL]

I should also mention that a good source for 1NB4-5036 chips is dead logic analyzer cards from HPAK's 167xx series.  A lot of these cards die from corrosion issues and sellers unload them on ebay conveniently "untested".

You can see the 1NB4-5036 chips near the input pod connectors.  Some of the more popular cards with 1NB4-5036 are 1671xA, 1674xA, 1675xA/B (but not 53A/B thru 56A/B).

The least capable card, 16715A, can often be found at scrap prices.  For example, here's one going for US$5 (plus shipping US$29, which makes is less of a bargain):

  https://www.ebay.com/itm/264812705935

But it gets you 8x 1NB4-5036.  Perhaps look around for something similar in the EU.  You could sell the ones you don't need.

[shakalnokturn]

Thanks again to both of you for your input.

I had an extensive search for 167xx (among others) L.A. boards on eBay in Europe there's nothing much going at interesting prices.
For now appart from sharing costs with someone in U.S. who would be in need of spares and willing to desolder and forward a couple I don't have any option that looks good. Maybe trying to use the 9th comparator on each IC if that's possible. I don't know yet, I haven't opened the MSO, I'm on holiday, I don't even have a screwdriver at hand.
(Yes, real TE adiccts buy scopes on holidays...)
I haven't been able to probe comparator outputs.

Funnily I didn't pay much attention to MarkL's waveform pictures, given pinout and speed requirements I assumed that the +/- 3.3V supplies would be for the actual comparator section and that the -5.1V would be for an ECL output to the fast digital capture. I must admit that I still don't understand the logic levels in that topic, even less considering that the -5.1V is also present on the resistor networks that follow the comparators.

The digital acquisition is fine, if I drive the front connector directly with the probe comp. output (that's all I have at hand) without going through the pod (yes, I've checked the pod is OK) the states will actually toggle. While doing this I noticed there was a fair deal more loading on defective inputs which made me suspect the input protection could be damaged.

I'd probably give toasting the diodes a try before replacing IC only once I had a good spare available.

Edit:
I forgot to mention that despite the two dead inputs this scope passes all self tests.

[MarkL]

Does the scope indicate explicitly that the comparators were included in the test?

If so, it's a good sign it passes, assuming the self-test is the same as that performed on the LA cards.  On the LA cards, the self-test puts the comparator in test mode which switches all the comparator inputs to an internal node (derived from pin 37), and then moves around the reference voltage.  This forces transitions that are seen by the digital acquisition chip inputs.  The test does not depend on the comparator data inputs, so this validates everything in the comparator except the input stage, and everything past the comparator.

It seems likely the 54622D is doing the same thing since this test mode is built into the comparator chip, and HPAK no doubt took advantage of that.  You could try to force a self-test error by lifting the leg on one of the comparator outputs to verify the self-test behaves this way.

For input verification, you could lift a leg on one of the bad data inputs, a leg on a good data input, and then compare the two while feeding the same signal to the two inputs on the pod.  If the signal appears the same at the now disconnected comparator pads, then the problem is almost assuredly the comparator.  This would also validate the signal path from the pod up to the comparator inputs and rule out any problems there.  Your test without using the pod is also a good indication, but I would be concerned that this is over-driving the comparator input and possibly causing some unintentional side effects and making it work (although admittedly rather unlikely).

I looked into sending you a couple of 1NB4-5036, but shipping prices are insane right now.  If you use a re-shipper from the US, I could do it that way.  PM me if you think you can work out a way.  The chips would be free; I have a pile of dead LA cards I've been using as donors.

No rush, enjoy your vacation.