Electronics > Repair
Fluke PM6666 counter freezing after 3 seconds from turning on.
<< < (22/27) > >>
0xdeadbeef:
My main point was: if this happens in lots of PM6666 counters (and it seems it does) and it is a process of deterioration (which it is in my case), there should be a common, typically aging related root cause. And a change of timing is something that caused similar problems in other cases. Programmers tend to rely on the timing that they saw during development. Things like performing a worst case analysis and explicitly waiting for the maximum time before trying to communicate with another IC is rarely done. Also adding an emergency break condition from a wait loop (that waits for some HW acknowledge) is something that is frequently forgotten.
thinkfat:
There is probably an aging related defect in the clock output, it looks like the high side mosfet of the output driver has deteriorated (electron migration?). That's why you see it improve with the pullup resistor connected. Would be interesting to see the clock waveform in your counter.
0xdeadbeef:
Didn't look into the schematics but is there actually a highside at all? That's not necessarily the case. Many designs just use a lowside output with passive pullup (i.e. "open drain"). Doesn't matter if the active edge is the falling edge - which it usually is.
pizzigri:

--- Quote from: thinkfat on October 14, 2020, 06:35:20 pm ---There is probably an aging related defect in the clock output, it looks like the high side mosfet of the output driver has deteriorated (electron migration?). That's why you see it improve with the pullup resistor connected. Would be interesting to see the clock waveform in your counter.

--- End quote ---
So essentially this is non repairable, at least not easily. Are you asking Oxdeadbeef for his waveform, or me for the original 10 mhz  clock from MTCXO?
Can the 500 ohm resistor create a potential damage or speed up deterioration ? I was going to Implement it ito increase reliability but I may actually get the opposite!
thinkfat:

--- Quote from: pizzigri on October 14, 2020, 07:27:52 pm ---
--- Quote from: thinkfat on October 14, 2020, 06:35:20 pm ---There is probably an aging related defect in the clock output, it looks like the high side mosfet of the output driver has deteriorated (electron migration?). That's why you see it improve with the pullup resistor connected. Would be interesting to see the clock waveform in your counter.

--- End quote ---
So essentially this is non repairable, at least not easily. Are you asking Oxdeadbeef for his waveform, or me for the original 10 mhz  clock from MTCXO?
Can the 500 ohm resistor create a potential damage or speed up deterioration ? I was going to Implement it ito increase reliability but I may actually get the opposite!

--- End quote ---

I wanted to see the 5MHz clock from his counter.

The 500 Ohm resistor is not really a good solution. I meant it mostly to check a theory of mine. Buffering the signal would certainly be better, but we still haven't found the actual reason for the hang. We know what causes it but not why.

You mentioned the GPIB card worked fine in another counter. Did you manage to use it for PC communication or was it just that it didn't hang the other PM6669 during boot?

Since we don't have a lot of options here, it's best to play the elimination game to isolate the fault. The IC105 (CPU) is socketed as well? Could you pull it and check if the 5MHz looks better then?

Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod