| Electronics > Repair |
| Series defect on agilent 167xx boards? |
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| DogP:
I looked more closely at the 16716A... I definitely don't see any corroded traces, and the few vias that had signs of corrosion look to be very minor (after cleaning up the little bit of green, there's plenty of gold still showing). I also took care of the glops of goo, which cleaned up well w/ alcohol. The QFP pins on U64 seem to be OK... I checked them under the microscope, and poked at each pin w/ tips of tweezers, and they all seem solid. I checked the LDO voltages, and I think they're OK based on calculating from the resistor values: U63: 1.53V U62: 2.14V U2: -1.70V U7: 3.33V So... I think I've checked the simple stuff that comes to mind. Any thoughts? Also, since I got the cables (why I bought that card in the first place), I was able to test the 16750B card w/ the Timing Zoom problem... it appears to only be an issue communicating with the Timing Zoom chips. I tested every channel in the regular logic analyzer mode, and they're all fine, but when I enable Timing Zoom, it'll sometimes throw errors about the WRAP flag, and looking at the waveform data, it's sometimes correct, sometimes not, and never aligned (e.g. I trigger the analyzer on the rising edge and see it at t=0, but the Timing Zoom waveform sometimes shows 0, sometimes shows 1, and never shows the edge). Interestingly, even with a constant '1' on the line, the timing zoom still sometimes shows '0'... though I've never seen a '0' show as a '1'. Thanks, DogP |
| MarkL:
Cool adapter! Please post some photos when you get it built and try it out. On the 16716A, there are some traces that run along the edge of the board that I've found are related to the board identification. (On other models too). The gray cable of course has to be installed. It's also involved in board identification. Attached is a photo of some severely damaged traces from a board that was not recognized. This board had other problems, but once these traces were repaired I could at least run pv on it. There are similar traces on the top side, but they were ok on this board. I would suggest finding the endpoints of these traces and check continuity from end to end and look closely around the gray cable area. Sometimes the corrosion gets under the soldermask and it's really hard to tell if a trace is good. A very sharp set of probes is useful to pierce the soldermask along the way, or use homemade probes from sewing needles. I have a set of Pomona 6275 probes with the stainless steel tips that I've sharpened to a very fine point with a hone. Yes, that 208-pin QFP is the host interface. It acts as an interface between the backplane bus and several on-board buses. Board ID is done through one of the on-board buses. On the 16750B, I think your finger poking test is a huge clue. I would get a scope on those zoom chip pins and see what they look like with the chip select test looping. Could you see any pattern to the zoom screen output? Were any of the 68 inputs working at all? |
| DogP:
>The gray cable of course has to be installed. It's also involved in board identification. LOL, thanks for pointing out the obvious... this board is missing the cable, and I was too busy looking for the corrosion that I didn't notice! :palm: Just swapped the cable from my other board and popped it in really quickly before leaving the house this AM, and it enumerated, and passed all self-tests! So, it looks like I just need to track down (or build) one of those cables. :) >I have a set of Pomona 6275 probes with the stainless steel tips that I've sharpened to a very fine point with a hone. Yep, those are the exact probes I have as well, and what I've been using to scrape the soldermask (as well as poking through the soldermask to check continuity). >Could you see any pattern to the zoom screen output? Were any of the 68 inputs working at all? The several I tested seemed to be partially working, but not fully working... though I need to test more tonight. It would sometimes correctly show that the pin was '1' when the pin was tied high, and would never show '1' when not, so it seemed to be somewhat connected to reality. But sometimes it'd show '0' when it was tied high as well, so it seems like more than just a time shift in the buffer. I plan to hook up the sig gen tonight and put in a square wave to see if I can catch any edges in Timing Zoom. Thanks, DogP |
| MarkL:
A further thought... You could get more precise with a finger poke by using, say, a 1k resistor connected to a fine probe to pull up or pull down various pins on the zoom chips to see exactly which pin(s) is being sensitive. The zoom chip appears to be a 3.3V part, or at least the bus interface is, so a pullup to 3.3V would be appropriate. U91 (all sections) and U92 (pins 1, 2, 3) are 2 input ANDs, and one input of each section is connected to pin 29 on the U29 Altera FLEX. The output of the 5 ANDs are each connected to one of the 5 zoom chips. In addition, one databus trace is connected to the other side of each of the the ANDs. So, the selection mechanism might be some kind of latched select depending on which databus trace is TRUE at the time. Perhaps it's valid to select multiple zoom chips at the same time for some operations. I didn't analyze it on a running system. Without getting too crazy tracing everything at the moment, I would add to my suggestion to also poke the 1k at U91 and U92. Sections [4,5,6] [10,9,8] and [13,12,11] of U92 appear to be unused and are left floating (which design-wise is not a good idea). One added word of caution... I've managed to kill chips on these boards with sloppy probing by dragging a probe from one pin to the next, essentially shorting two adjacent pins together. A couple of comparators met their demise because of this, but it could happen to any chip. |
| DogP:
--- Quote from: MarkL on February 18, 2022, 09:35:56 pm ---You could get more precise with a finger poke by using, say, a 1k resistor connected to a fine probe to pull up or pull down various pins on the zoom chips to see exactly which pin(s) is being sensitive. The zoom chip appears to be a 3.3V part, or at least the bus interface is, so a pullup to 3.3V would be appropriate. U91 (all sections) and U92 (pins 1, 2, 3) are 2 input ANDs, and one input of each section is connected to pin 29 on the U29 Altera FLEX. The output of the 5 ANDs are each connected to one of the 5 zoom chips. In addition, one databus trace is connected to the other side of each of the the ANDs. So, the selection mechanism might be some kind of latched select depending on which databus trace is TRUE at the time. Perhaps it's valid to select multiple zoom chips at the same time for some operations. I didn't analyze it on a running system. Without getting too crazy tracing everything at the moment, I would add to my suggestion to also poke the 1k at U91 and U92. Sections [4,5,6] [10,9,8] and [13,12,11] of U92 appear to be unused and are left floating (which design-wise is not a good idea). --- End quote --- Thanks for the info... yes, I definitely plan to do a more precise "touch". Though the interesting thing I guess I didn't mention is that I don't have to be physically touching the pins to induce the failure. Just having my finger nearby, or even touching the top of the plastic chip can cause it. Just a guess, but the chip might have a VCO running inside it to get the 2 GHz timing, and my finger nearby is coupling, inducing a signal on whatever pin(s) are floating... or maybe just added capacitance... or magic? ;) --- Quote from: MarkL on February 18, 2022, 09:35:56 pm ---One added word of caution... I've managed to kill chips on these boards with sloppy probing by dragging a probe from one pin to the next, essentially shorting two adjacent pins together. A couple of comparators met their demise because of this, but it could happen to any chip. --- End quote --- Yep, that's one reason I haven't done much probing yet... those are really fine pitch QFPs, not conducive to probing. I plan to test as much as possible at the SO resistor networks, test points on the bottom of the board, vias, etc. But I've got some mapping to do... Thanks, DogP |
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