| Electronics > Repair |
| Fluke PM6666 counter freezing after 3 seconds from turning on. |
| << < (21/27) > >> |
| thinkfat:
Don't go too crazy on the resistors. If the counter doesn't boot any more, that's a clear signal to stop what you're doing. If you damage the ASIC you have a paperweight. The first attempt more or less proves that there is a problem either with the output driver or with the CPU (IC105) loading the clock signal too much. I'd now try recovering the clock with a buffer only for the GPIB card. |
| 0xdeadbeef:
Could be something totally unrelated though. Like due to aging of some component the GPIB card takes longer to boot but the CPU already started the I2C communication before the card is able to properly react on that. So it missed the request to answer and thus the CPU is blocked since it waits for an answer. Or something like that. |
| thinkfat:
--- Quote from: 0xdeadbeef on October 14, 2020, 03:15:55 pm ---Could be something totally unrelated though. Like due to aging of some component the GPIB card takes longer to boot but the CPU already started the I2C communication before the card is able to properly react on that. So it missed the request to answer and thus the CPU is blocked since it waits for an answer. Or something like that. --- End quote --- The GPIB card pulls the SCL line low doing "clock stretching". The CPU is blocked waiting for the I2C bus to return to idle. It continues normally once you disconnect the SCL line to the GPIB card. |
| 0xdeadbeef:
Well, it's not really clock stretching in its usual meaning since it obviously continues forever. And one reason for this might be that the card's I2C state machine is confused because of timing issues. |
| thinkfat:
I think so as well. What I imagine happening is that the I2C part of the GPIB CPU has a hardwired state machine driven by SCL. As soon as it receives its slave address it pulls SCL low to stall the master, then issues an irq. The processor part would then act on the interrupt and carry out whatever reaction is programmed. This part does not happen and so the bus stays blocked. |
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