K8063 board failure

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1

I have a Clock system that uses 2 sets of 6 K8063 units to give two clock displays. The Displays are driven by a PIC processor board. The system has been running for the past 6 years. I have 5 of these double display clocks which have worked as expected for a significant time.

However:

One digit in one display has developed a fault. It is the last board in the chain and so has terminating resistors. If the board remains connected to the series then the whole display freezes with no data updated to either display. If I disconnect the board then both displays update as expected. ( Hours, minutes and seconds) The fault is not the MCU because if I swap that to the next board then it drives the display correctly ( although in the wrong place). The faulty board does go through the self test OK. I suspect the fault lies in the RS232 circuitry.

Are there any further tests I can make to find the problem? Although this suggests the need to trace, remove and replace one or more components.

Or are there any other options to repair or replace the board.

Thanks

Ted

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For information - further investigation which included replacing the ‘faulty’ digit suggests that the problem lies further up the chain. The Master display is in one case with the processor board and the slave display in a second case with a cable ± 50m carrying the serial signal.

By a process of substitution it now looks as though the fault lies in the serial output from the PIC processor board I am using. Possibly caused by some system “testing” which resulted in an incorrect connection.

I don’t fully understand why attaching the slave unit and cable causes the master unit to freeze - presumably related to the output on the MAX232 line driver chip.

You may wish to note that distance the signal normally works!