Electronics > Repair
Series defect on agilent 167xx boards?
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MarkL:

--- Quote from: DogP on February 10, 2022, 02:34:56 am --->I buzzed out those two vias.  I called them A and B.  Photos attached.
Thanks!  Though the damaged vias don't visibly connect to anything, so there should be at least two endpoints for A and B, right?  Any idea where the other end(s) connect to?  Hmm... maybe the hybrid(s) since they're suspiciously close by?
...

--- End quote ---
Yes, sorry for not engaging brain before posting.

Below is the other end of A, and one other place where B shows up.

I believe B is actually the -2V (-2.1V) supply.  It has a very low resistance to the output leg on the regulator.  If you look at the two locations where I found B in the bad area, it's connected to a decoupling cap to ground and a 68.1R resistor to a signal trace.  So B appears to be providing power to some ECL terminations.  Since the -2V supply is everywhere, it's really hard to say where that specific via goes on a working board.  The closest connection is what I've shown, which is my best guess.  It's not on any pins under the hybrid.

If your continuity on the via gets broken while you're fixing it, you'd be in a better position to verify the actual connectivity.

I would consider it a last resort, but it is possible to excavate the via if you can't get a reliable connection from the top or bottom.

EDIT: Oh, and one further note.  I did take a look at A and B with a scope.  Unsurprisingly, B doesn't move.  And A appears to be TTL and changes state while calibrating the logic trigger.  Not very exciting.
DogP:
Awesome... thanks for checking these!  Hopefully I can make a permanent repair to this tonight.

I haven't made any useful progress on the 16750B... I don't have any cables for these boards, so I can't test with any real signals at the moment.  I ordered a 16716A (parts board) w/ cable set, so I plan to put this repair on hold until the cables arrive.  I'm hoping if I can drive some signals into it, I'll be able to see what's actually working/not working better.

Of course, then I'll have a (likely dead) 16716A, which I'll want to try repairing too. :-P

I do plan to dig through some binaries and see if I can figure anything out on the WRAP flag.  I'm wondering if it's specific to the zoom chips, is it connected to the FLEX FPGA or another chip, etc.  Then maybe I can see how many of the zoom chip pins are shared, and which go back to the FLEX, and compare between the A and B boards that I have.

Thanks,
DogP
DogP:
Any chance you could double-check the measurements?  In my "currently working" state, I measured to confirm mine was actually making a good connection, even in the poor hacked state.

I get 0 ohms to your first point 'A', but would briefly get a beep on the 2nd point 'A', but showed about 230 ohms steady state.  If you can confirm this is 0 ohms on yours, I'll just add a jumper wire.

On 'B', I was getting about 9 ohms.  I probed around a bit, and found this ferrite near U502 that actually looked like 0 ohms.  Though I didn't find any other places this went, so I wonder if my repair is only half connected.  Can you see whether you get similar measurements with that ferrite, and if there's anywhere else you find it connected?

You might be right about excavating the via.  Since I've already soldered to mine, it's a bit messy and hard to see... if you shine a bright light behind your vias, can you see a trace leaving the sites, and if so, in which direction?  With the ground and power planes nearby, it's probably tough to see.

Thanks again!
DogP
MarkL:
On the two "A" points I'm getting 1.2R, which is not too unreasonable but perhaps a bit high.

On B I'm getting 0.133R.  There are a lot beads in this section which are going to be low resistance and it's hard to tell which side we're on.  I used a high current across the two B points (1.5A limited to 0.4V) when I was searching and I couldn't find any components that had voltage drop across them, and an IR camera did not light up on anything.  It seems likely that the B via near the edge would have another leg or two coming off it given where they put it.

Do you know a friendly dentist or vet who would xray these areas for you?

If you want to hold on making any permanent repairs, I can do this later today:

- I will try to find the exact card type you have and double check the continuity.  I have a pile of these cards, and all of them are (or at least were) working.   I've been testing with a card that is the same as yours in these sections, but who knows.

- I will try a different tracing method.  I have a PCB track current probe (I-prober 520) and I will inject a signal between the seemingly connected points to follow the exact path of the buried traces.  I'll try to find and trace all the end points with this method too in case the signal splits into multiple paths at the damaged vias.
DogP:
If you don't mind doing further tests, I can certainly wait... but I appreciate the confirmation!  I just wanted to make sure it wasn't a case of quickly probing w/ a DMM continuity checker without noting the actual R value.  Of course I wonder why mine is higher resistance, but maybe it's just part of my board's defect(s).

>Do you know a friendly dentist or vet who would xray these areas for you?
Unfortunately, no... I tried to convince my boss to buy one a few years ago, but couldn't justify it.  I personally have a scintillator, but no xray source (nor safe way to operate one!).  Someday... ;)

Thanks,
DogP
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