The pods are passive, and there are also a few passives on the system board before the signal reaches the 1NB4-5036 comparators.

The PCB layout in that section is simple.? You should be able to easily trace the failing D0 and D8 digital signals all the way to the comparator pins.? Compare a test input signal at various points between dead and working channels.? Each comparator handles 8 inputs on this scope, so D0 and D8 are on different comparators.

It's usually the comparator that dies, but it's also a little suspicious that it's the lowest order bit on each group of 8.

At least start with tracing through to the comparator output.? Does the scope pass all the self tests?

If it is the comparator(s), these can be found on a lot of different HPAK gear for salvage.? There's also at least one ebay seller who has them.

-mark

I should also point out that the 1NB4-5036 comparator has 9 channels and you only need 8.

If the comparator(s) is indeed bad, I recall someone who was asking questions about rerouting the dead channel to use the extra channel.? For them, a replacement comparator was not an option.

They didn't post back to say if the mod was successful, but it should work if you're stuck without access to a replacement.

FYI,

-mark

The last time I looked inside a digital pod, (for a different make of logic analyzer, it was mechanically damaged...)

There were some ceramic hybrid electronics.? Not 100% sure, but High Speed, High Z input to balanced output drivers I think, for the twisted pair (per bit) cable to the instrument.? (So the loading on the digital system that you are investigating is minimal.)

I don't know the 54622D, but I'd expect a service (or even the user) manual to have some clues to the exact nature of the logic pod..

Regards.

Dave G8KBV.

--
Created on and sent from a Unix like PC running and using free and open source software:

*IF* the pods are the same as the basic 166x, 16500x, 16600x, etc then you can look for the following:

the input impedance of the logic analyzer is 10K.? In the pods is a resistor network of 7pf in parallel with 90.9K.? This network is available from HP to be put into a board.? This network should be in the squid adaptor, and this network should be in the pod adaptor (20 pin to LA)

The cables are, if woven, made from nichrome wire having a series resistance of 200 ohms, probably a reason why a straight wire cable from the LA (40 pins) to the adaptors (40 to 20,? etc) may not work as well.

That resistor network forms a 10:1 divider with frequency compensation.

Some of the LA modules have stimulus/digital pattern generators. Those can be TTL, or ECL.? It is possible that what you saw was an output driver if it were differential.? The 16500 modules were 16520, 16521, and 16522.

The intended connection scheme was a squid adaptor to dip clips; use a pod adaptor to a 20 pin socket installed on the board (I do....), or a direct connection with the compensation network on the board (I don't).? There are more expensive connection schemes involving mictor high density connectos.? Those I have decided are too expensive.

Harvey

The pods are passive, and there are also a few passives on the system board before the signal reaches the 1NB4-5036 comparators.

Thanks all! I have other scopes so I can open up and trace the signals. It is quite possible that something can have whacked the comparators. Something like an ESD pulse. I have not opened the scope since I replaced the battery in 2016.

So, yeah, it would be good to check that the probe cable and any flying leads are ok before going inside, as Harvey and Sam point out.? The 54622D pods are electrically the same as the later model logic analyzer pods mentioned.? The nichrome signal wire in the weave can break if the cable is pulled or mishandled, and I've also had bad flying leads (which can be easily replaced).? It's best to check the resistance from the very tip of the flying lead, assuming that's what you're using.

Dave_G0WBX: You probably saw the insides of one of the pods from an early model logic analyzer, such as this one on a 1631D:

? https://www.eevblog.com/forum/testgear/hp-1631d-logic-analyzer/msg1213751/#msg1213751

That is not used on the 54622D.

-mark

I will look into this later. Starting with checking the probes: FWIW is the service manual (sorry excuse for) here:?

I ordered two from eBay, but while we are at it... Would it be a good idea to create a protection circuit with say?RCLAMP0508M.TBT TVS protectors and put before the probes when working on "dangerous" circuits? Those ports blew when I was working on? a new memory board I am trying to build for a HP1000 A400

Thanks all! With the help of a friend who:
a) Is younger and has better eysight
b) Is in possession of better desoldering gear
c) Has more exeperience

We replaced both comparators (ch 8 and ch 1 broken). We noticed that the solderability of the chips was so-so, possibly because they were manufactured some 20 years ago. Wonder if there is a good procedure to restore solderability of old chips?

Anyway. These links ars good:


The latter has a post with ppin descriptions that should help with troubleshooting.

Use proper (= leaded) solder instead of the early, so-so, RoHS soldering on those scopes. That might help.

While there: carefully check for tin whiskers too!

Wilko

Depending on where the chip came from, it might have been
left over from a gold harvesting operation.

The modern gold prospectors soak gold plated IC's, etc... in
aquaregia, to remove the gold plating, without removing much
of the base metal (steel).

Typically, the leads will appear to have a purplish cast after
this has been done, and won't solder worth beans.

-Chuck Harris

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My vote for best aqua regia story is how de Hevesy hid two Nobel medals from the Nazis by dissolving them (the medals, not the Nazis) in aqua regia. After the war, the gold was recovered and the medals reconstituted.

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

Having made about 200 gallons at my first job, I can say it
is pretty impressive stuff. It took about 1:3 mixture of nitric
and hydrochloric acids, and as I recall a dash of sulfuric.

I think the sulfuric was to improve the way it worked in our
application.

We mixed it up in a big stainless steel tub that sat under a
vent hood. It was used to remove the zinc from brass boxes
in prepping them for silver plating.

I also used it to remove silver plating from boxes that needed
to be reworked. New silver plating won't stick to old silver
plating.

As I recall, our last stage in plating was to dip the plated
items in a potassium chromate solution. This put a thin layer
of chrome metal on the silver plating, and made it possible
to handle the plated boxes without leaving ugly finger prints.

The chrome prevented new plate from sticking to the old plate...



-Chuck Harris




On Mon, 08 Apr 2024 11:35:15 -0700 "Jim Ford" <james.ford@...>
wrote:

Aqua Regia, Latin for Royal Water, is a mixture of hydrochloric and
nitric acids. ISTR that neither acid by itself works very well on
precious metals like silver and gold.? Something about nitric acid
being a good oxidizer?? Been a few decades since I've heard the term
Aqua Regia.? Please correct me if I'm wrong.? ? ? JimSent from my
T-Mobile 4G LTE Device -------- Original message --------From: Chuck
Harris <cfharris@...> Date: 4/8/24 8:27 AM (GMT-08:00) To:
[email protected] Subject: Re:
[HP-Agilent-Keysight-equipment] Agilent 54622D with broken digital
inputs - Fixable? Depending on where the chip came from, it might
have beenleft over from a gold harvesting operation.The modern gold
prospectors soak gold plated IC's, etc... inaquaregia, to remove the
gold plating, without removing muchof the base metal
(steel).Typically, the leads will appear to have a purplish cast
afterthis has been done, and won't solder worth beans.-Chuck HarrisOn
Mon, 8 Apr 2024 17:18:01 +0200 "Wilko Bulte" <wkb@...> wrote:>
Use proper (= leaded) solder instead of the early, so-so, RoHS>
soldering on those scopes. That might help. > > While there:
carefully check for tin whiskers too!> > Wilko> > > > >

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De Hevesy worked at the Niels Bohr Institute. That's probably what confused you.

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

Lovely story Tom! My question would be how does one recover the shape of the medal from the aqua regia? By asking politely?
Renaud