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Anritsu MS2721B internal CF card missing
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brainstorm:

--- Quote from: analogRF on October 06, 2021, 02:59:20 am ---
the problem you are describing still very much looks like the memory (RAM) issue that I had some time ago...the symptoms were very similar to what you describe although I didnt do that much deep measurements as you have but i did measure "bad looking" signals on the memory chips
and started changing them randomly (starting from the bottom) and after the second chip the unit came back to life...maybe with deeper dive you can even pinpoint which memory it might be, i just had a strong suspicion by the general look of the signals on the data lines..changing those chips is relatively easy...maybe you have already done that?


as a general rule, I have come to the conclusion that when an instrument stops so early in the boot process, usually (i am not saying always) my first suspect is the RAM and then the bootrom wherever it is. this has been the case in multiple occasions in various instruments at least for me...

--- End quote ---

I just received fresh RAM chips... I see some jitter on some of the address lines, but I'm not sure if it's just a bad trigger setting or legit. How did you determine "bad looking" signals, @analogRF?
analogRF:

--- Quote from: brainstorm on November 05, 2021, 11:26:50 am ---
--- Quote from: analogRF on October 06, 2021, 02:59:20 am ---
the problem you are describing still very much looks like the memory (RAM) issue that I had some time ago...the symptoms were very similar to what you describe although I didnt do that much deep measurements as you have but i did measure "bad looking" signals on the memory chips
and started changing them randomly (starting from the bottom) and after the second chip the unit came back to life...maybe with deeper dive you can even pinpoint which memory it might be, i just had a strong suspicion by the general look of the signals on the data lines..changing those chips is relatively easy...maybe you have already done that?


as a general rule, I have come to the conclusion that when an instrument stops so early in the boot process, usually (i am not saying always) my first suspect is the RAM and then the bootrom wherever it is. this has been the case in multiple occasions in various instruments at least for me...

--- End quote ---

I just received fresh RAM chips... I see some jitter on some of the address lines, but I'm not sure if it's just a bad trigger setting or legit. How did you determine "bad looking" signals, @analogRF?

--- End quote ---
i think since it is not periodic signal it is hard to distinguish jitter. But what I clearly saw was (1) runt pulses with either top not reaching the HI or the bottom not reaching the LO level (2) pulses that were much narrower than they should be
if there was any jitter I could not distinguish...it is not periodic so I could not trigger on them...
brainstorm:
Thanks, that makes sense, did not realise jitter does not matter as much when addresses (the pins I was probing: A0, A1, A2...) can just latch randomly.

While flipping the board on the table, I've noticed that the LAN91C111 IC (https://ww1.microchip.com/downloads/en/DeviceDoc/00002276A.pdf) was rather hot to the touch (not painful but uncomfortable)... thermal cam says 52C.

If you still have the board around, would you mind touching that IC on boot? It could be that this one is bringing rails down and triggering PWR_FAIL signal (which is high at 3.3V on my board).
analogRF:
i dont have the board anymore but that is DEFINITELY a big find. Has there been any sign of water damage on the board?
the LAN chip should not be that hot...what if you let it run for like 5-10min and monitor temps?

I once repaired an anritsu S331E that could not boot and there was water damage on the board
I repaired the power supplies and they were all ok and it still could not boot until thermal camera
came in and told me that the the USB controller chip was about 55-60C but all voltages were ok
so I replaced that chip (unobtainable except from china) and it worked  :D
so why dont you also try to probe around that chip...
cpu getting to 50-55C maybe is ok but the lan chip ?? I dont think that's normal at all....specially when it is not connected to ethernet

I now suspect the FW is stalled because at one point it must initialize the LAN interface and it can't ...

brainstorm:
Fortunately that IC is really cheap and seems like it's obtainable :)

After running for 5min the temperature stays stable at 53C at 14V and 300mA... that's a bit more than 4W and it seems that it might be taking almost all of the current state's power budget since all other ICs are hovering 30C :)

Thanks for the hints and experience with those things! I think test some of the pins (any recommendations on what I should see?).

I think I'll order one of those LAN91C111 anyway and replace, looks like a winner... I hope no other passives around it are toasted and/or cause it to fail that way.
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