RS232 data communication issue

Discussion in 'General Electronics Chat' started by Jim_cliff11, Sep 13, 2016.

  1. Jim_cliff11

    Thread Starter New Member

    Sep 5, 2015
    18
    0
    Hi all,

    I'm having an issue with an old CNC machine built in the early 80's. The machine is an Anilam Crusader 2 which consists of 3 servo motor powered axis' and 3 glass linear scales on a Bridgeport milling machine. Surprisingly for its age, it actually very accurate and precise. I can program the controller through the console, however this is long winded and there is no way to save entered programs. The console does however have an RS232 DB25 port on the back for communication with PC via DNC or CAM.

    I know the machine is set up for RS232 communication (Correct on-board software) and wiring. I'm trying to do a basic loop back test on the Crusader by jumping the pins on the RS232 DB25 connector. This is instructed in the user manual as a self-test to ensure the RS232 communication IC's on the Crusader are functioning. Below is a pin out of my jumper and the corresponding pin descriptions:

    Jumper.JPG

    When i run the test on the machine with the jumpers attached to the pins I receive an error. This error number relates to: "UART Fail - Using the self test for RS232 this portion of the CPU has failed". As all the solders, tracts and pins on the PCB are good I'm assuming one of the IC's has failed. This is where it gets out of my depth!! I have wiring diagrams for all the other boards bar this one.... typical. I've identified all the IC's on the PCB (see below):

    PCB-499 chip labels.jpg
    Note: Only 5 of the 10 DIP pins on the PCB are used for RS232 comms.

    I've also traced each RS232 DIP pin back to its relative IC pin (see below):

    PCB-499_1632x1216.jpg

    I'm convinced the issue lies within either the MC1488P driver, the MC1489PC receiver or the COM5016 baud rate generator. However I'm unsure as to how to test them and exactly what they do and how they work. Which IC deals with the UART error? What is UART?

    I'm fairly capable of this repair, I just need a little guidance from those with much more knowledge than me. As Anilam do not support this product anymore and were bought out years ago I cannot go to them.

    Thanks in advance for the help.
    Jim
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    UART is an acronym for Universal Asynchronous Receiver Transmitter.

    A 1488 driver has four NAND gate drivers in a package. The inputs are TTL compatible and the outputs are RS-232 compatible.
    A 1489 receiver has four Schmitt Trigger receivers. The inputs are RS-232 compatible over the full ±25 volt range and the outputs are TTL compatible.
    The COM5016 baud rate generator is responsible for generating a clock signal that is (usually) 16 times the communication baudrate. For example 2400 baud (bits per second) was a fairly standard rate at the time the unit was manufactured. The Rx/Tx clock to the UART would be 16 x 2400 or 38.4 kHz.
    If you keep looking for chips you are sure to find the actual UART. If I was to take a couple of wild guesses it might be a GI AY3-1013, or an Intel 8251, or a Motorola MC6850.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    What test equipment do you have?
    Digital mulimeter?
    Oscilloscope?
    PC with a 25-pin comm cable?
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    The 8251 is onboard given.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Most problems are with the 1488/89 IC's.
    They are common IC's and easily changed, use a dip socket when replacing.
    I usually use a 3 wire cable with 2,3,7 for communication and 4-5 and 6-8-20 jumpered.
    Max.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    Sorry, I missed that. Can you show me where that was stated in the original post?
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    It was in the second photo posted.


    Anilam PCB-499.jpg
     
  8. Jim_cliff11

    Thread Starter New Member

    Sep 5, 2015
    18
    0
    Invaluable information chaps, thanks for your replies.

    I will see if I can source some replacement 1488, 1489 and an 8251. By the sounds of it then, the M5L8251AP is the major IC which could be at fault here? Is there any way to test these chips?

    My test equipment consists of a multi meter, oscilloscope and PC with RS232 DB9 connector.
     
  9. Jim_cliff11

    Thread Starter New Member

    Sep 5, 2015
    18
    0
    Update: Fixed it!!! Believe it or not I had a spare M5L8251AP chip burried which hasnt been touched in 20 years. Swapped them over and fired it up. Ran the test and all is good.

    Thanks for the help chaps! Much appreciated.

    Jim
     
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