Hardware Bugs

Known Hardware Issues and Bugs

• The limit of 128 colour palette as opposed to the desired 256 was alledgedly due to not having enough spare physical pins on the ASIC’s die to accomodate it.
  
• When the reset button is pressed the SAA1099 sound chip is not reset so notes being played will continue.
  
• The ASIC does not send an 8Mhz reset signal to the Sam Drive disc controllers when the Reset button is pressed which can cause corruption to a floppy disc left in the drive - hardware fix is the DPU by Edwin Blink
  
• The NMI button is not debounced causing multiple NMI’s to be generated - hardware fix is the NMI Debounce by Edwin Blink. The Messenger included a separate NMI board to get around this issue.
  
• The MIDI ports alledgedly do not work as explained by Steve Nutting in Fred 2
  
• A missing capacitor causes reflection interference on screen - hardware fix from Edwin Blink
  
• The serial port on the Comms Interface has a hardware bug as listed in Format Vol.5 No.8 where you get transmission errors after 100-200 characters regardless of baud rate. This is due to an electrical supply issue in the board which needs smoothing. To fix, solder a fat tantulum cpacitor between the 0v and +5v across the supply lines near R3.
  
• The Sam Mouse interface can also be erratic due to the same power issue - the HCT chips in it don’t like the SAM’s glitchy supply so shove a couple of the biggest capacitors you can find inside your SAM across the +5v and 0v rails. from Simon Cooke on the Sam Users Mailing List October 1994.

See also ROM bugs