| Electronics > Repair |
| Fluke PM6666 counter freezing after 3 seconds from turning on. |
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| thinkfat:
You guys haven't been singing along. The IC2 on the GPIB card is pulling SCL low when it's being accessed. I2C slaves can do that, it's called "clock stretching". The bus master then must wait until the slave releases SCL (never happens) which is the very reason why the counter hangs. Proof: counter continues as soon as you disconnect the SCL line. |
| coromonadalix:
got schematics for the 6666 Well the OP did say the gpib card whas working fine in other instrument, did i read it wrong ? reply #19 Could it be simply incompatible with the 6666 ? if everything else works and the gpib works in a 6669 what can we do to solve this ? Is the jp101 test norm jumper closed or open ? |
| khs:
--- Quote from: thinkfat on October 12, 2020, 07:37:42 pm ---You guys haven't been singing along. The IC2 on the GPIB card is pulling SCL low when it's being accessed. I2C slaves can do that, it's called "clock stretching". The bus master then must wait until the slave releases SCL (never happens) which is the very reason why the counter hangs. Proof: counter continues as soon as you disconnect the SCL line. --- End quote --- :-+ :-+ :-+ |
| thinkfat:
I found a datasheet for the MAB84X1 series. The clock input is specified as HCMOS and TTL compatible so we're good here (though I think 3.8V still a bit low), but the maximum rise and fall time of the clock is <10ns. Can you check the clock edges meet that spec? |
| thinkfat:
--- Quote from: coromonadalix on October 12, 2020, 08:47:05 pm ---got schematics for the 6666 Well the OP did say the gpib card whas working fine in other instrument, did i read it wrong ? reply #19 Could it be simply incompatible with the 6666 ? if everything else works and the gpib works in a 6669 what can we do to solve this ? Is the jp101 test norm jumper closed or open ? --- End quote --- You're right, the GPIB from the PM6666 is working in another counter, and the GPIB from that counter also fails in the PM6666. That's why I keep pressing on thoroughly checking the 5MHz ;) PS: if you have a function generator, try connecting a 5MHz square wave from the generator to the GPIB module, instead of sourcing the clock from the PM6666. If it works then you have found your culprit. Then you need to find out how to restore or improve the 5MHz clock. Maybe add a 74HC14? |
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