Hi,
Am doing a repair job on a Point of Sale (POS) terminal which has the problem of the motherboard's printer socket of failing to recognise the existance of the printer (the receipt printer is connected to the terminal's motherboard via a connector).
Was told to change the NPN Darlington transistors (2pairs): one pair is controlling the slip printer and the other pair is for the roll printer. The transistors used are Sanken Electronics's SL4031. Some other boards use Fujitsu Microelectronics's FT5754M. For this particular board, the original transistors are Sanken's but I am using the Fujitsus.
After soldering them and powering on the terminal, the printer can be switched on (it is powered on via the connector thru the motherboard printer socket). The terminal can be powered on but there's no display: just a lit-on screen.
Burning smell is present from the motherboard. The terminal still could not detect the slip printer. Error message is "Printer not installed". One motherboard LED indicator is not lit and the LED for the printer sockets is flashing.
Any advise is welcome. Thanks.