Acorn computer A3000 Servicing
Also see for A3000: Welcome guide
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Common PCB problemsThere are a number of problems with the circuitry of the machines which can lead toproblems, especially in the peripheral area. These are detailed below, with details of causesand possible remedies.Serial PortThere are a number of problems with the serial interface circuitry in the machines.Baud rates. Many machines nowadays (including cheap Taiwanese PCclones) are capable of running their serial ports at 38.4kbaud and even115kbaud. The Archimedes/A3000 is limited to 19,200 baud, which proves to be alimiting factor if the machine is used with the latest types of 9,600 baud modems withdata compression.Split baud rates. For many applications, the serial port is run with transmit andreceive baud rates set identically. If they are to be different, then only the transmitbaud rate will be set accurately. This is not a problem, provided that the receiverate is low enough that the small error in its frequency is insignificant. As aguide, 1200 baud will work fine, but 9600 will not.Line levels (not A3000.) The serial port on Archimedes drives the line with +/5Vlevels, to the RS423 specification. This will drive most RS232 peripherals, althoughthe RS232 spec. calls for levels of +/-9V or greater. Some RS232 peripherals,however, will not work correctly with the Archimedes' levels.Failure to comply to standard (A305/A310/A440 only.) The early machines werefitted with a serial port chip which failed to implement the RS423 protocol correctly,which caused data to be corrupted. RISC OS contains a software patch which willcure the problem; for those with Arthur 1.2, the RS423 Line Driver patch is amodule available from Acorn. This is not a problem with A3000 and A4x0/1machines.Buffer failure. There have been reports that the buffers which buffer RS423 in andout of the machine are prone to failure. |
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