Electronics > Repair

Series defect on agilent 167xx boards?

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John_ITIC:
My burnt 16754A came back from the dead after I replaced the FPGA. So, that is the solution if anyone makes the same mistake I did (connect via 80 pin flat cables).

I have noticed that the board-board interconnect connectors are also corroded on the bottom side. See attached images. After scraping off the green corrosion, I can see that the gold flashing is gone and a brown discolored surface is underneath. I suspect this will not make good contact so, in order to do a proper refurbishment, it would be nice to replace these connectors.

Does anyone happen to know the part number of these connector?

The flex connector cable that goes between the boards has HP/Agilent part number '16754-61601' (picture attached). The Part # 16754-60002 is the set of two.

Thanks,
/John.

MarkL:

--- Quote from: John_ITIC on March 26, 2024, 07:05:55 pm ---My burnt 16754A came back from the dead after I replaced the FPGA. So, that is the solution if anyone makes the same mistake I did (connect via 80 pin flat cables).

I have noticed that the board-board interconnect connectors are also corroded on the bottom side. See attached images. After scraping off the green corrosion, I can see that the gold flashing is gone and a brown discolored surface is underneath. I suspect this will not make good contact so, in order to do a proper refurbishment, it would be nice to replace these connectors.

Does anyone happen to know the part number of these connector?

The flex connector cable that goes between the boards has HP/Agilent part number '16754-61601' (picture attached). The Part # 16754-60002 is the set of two.

Thanks,
/John.

--- End quote ---
I believe it is 3M Pak 8 Plug Connectors and Pak 8 Socket Connectors (previously Robinson Nugent, acquired by 3M).  Board side here:

  https://www.3m.com/3M/en_US/p/d/b30000132/

The part number looks like it should be P08-100-SLxx-A-G, where the xx depends on packaging and vacuum pickup options (see datasheet).  It's not in the datasheet as a contact quantity option, but it does show up as an obsolete part.

I've used a fine SS brush to get most of the corrosion off, and sometimes had to pick off the remaining pieces with a needle.  But that unfortunately took a fair amount gold plating with it as you also experienced.  However, the connectors still seem to work ok.  Longevity may be an issue.

They can also be stolen from the top side of dead boards where they are usually corrosion-free.  The heating cycle needs to be carefully controlled as they are easy to deform (see datasheet for process rating).  I would use Chip Quik or other low melting point alloy to get them off.

Hamster:
tarnix may help remove the corrosion as well.

John_ITIC:
MarkL was kind enough to send me a few spare comparators for my "burnt" 16754A board. I soldered one in but that board still fails the adcTest (pv shows no response from the ADC [U54, bottom side, TLC2543C]). I put the scope on it and there is no activity from the host while running the adcTest. I also swapped U54 with another board and the errors stays with my "burnt" board. As a test, I also swapped the U144 (LVT16245A) as I figure this line driver might be involved in the host communication - still no improvement.

So, there is a good possibility something else got damaged on this board when I used those 80 lead flat cables. Perhaps some internal trace got burnt off? Hard to tell.

So, at this point, I have seven working 16754A's, one working 16756A and two bad 16754As. I will upgrade the 16754A's to 16756A's via removal of resistor B3 (image attached).

Of the seven working 16754A boards, most are failing the RC comp and tap delay tests (timing zoom). I will have to continue that research at a later time as I'm sort of stuck at that issue.

At least I can be sure that no further deterioration will happen due to rail corrosion so I can push further investigation into the future. And I have more boards than I need, really.

I now have multiple TDS5xx, TDS6xx and TDS7xx scopes I need to attend to - the usual recapping and saving of battery backed SRAM + upgrade to new SRAM modules. I'd better get to that before too late.

Thanks,
/John.

FrodeM:
I just though this might be worthwhile to mention..

Got a 16534A today, with crusty rails. Fortunately, no matter how bad it looked, the card passed the GUI selftests and after removing the gunk it seems like all traces are indeed intact (although small discoloration on two and ). However, one thing I noticed is that there was a decent amount of corrosion on the underside bracket for the heatsink mounts.

Reading though various threads, there's some suggestions that the corrosion is caused by moisture collecting. Given my observation, and the nature of the corrosion, I would rather think that the cause here is fumes released by the rubbery tape as it decomposes, in combination with moistures in the air. That would also explain why the corrosion in some worst-case examples is able to penetrate vias and even cause corrosion across a significant area of the top side.

On that note, it would at some point be great to figure out what precisely is the cause of this corrosion. Eventually if it can be properly neutralized as a part of the repair process (given some claim it may reappear after some time, if just washed with IPA. I know battery-leak corrosion on old motherboards is often handled with vinegar, but the chemistry for that is pretty well known. I don't want to try anything like that here unless I know it works and is safe for the boards.

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