UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - New restoration project - Roland XP-50

kevinaston1 · 28th Jan 2018, 1:27 am

The LCD contrast is controlled via the CPU, IC20. A PWM signal goes to IC17, and is integrated to provide a d.c. contrast control level at pin 7 of IC17; High is no contrast, Low is full contrast.

Measure this point to find out if it is simply the LCD contrast. If it is stuck high, just work back toward the CPU, varying the contrast control as needed to find out where the circuit is not playing.

If you want to force the contrast high, ground pin 3 of CN14 to enable you to evaluate the rest of the keyboard, and note any other faults.

Roland very helpfully provide decent self test routines, as shown in the service manual.

Regards.

Kevin

28th Jan 2018, 1:27 am	#5
kevinaston1 Hexode Join Date: Aug 2014 Location: Featherstone, West Yorkshire, UK. Posts: 386	Re: New restoration project - Roland XP-50 The LCD contrast is controlled via the CPU, IC20. A PWM signal goes to IC17, and is integrated to provide a d.c. contrast control level at pin 7 of IC17; High is no contrast, Low is full contrast. Measure this point to find out if it is simply the LCD contrast. If it is stuck high, just work back toward the CPU, varying the contrast control as needed to find out where the circuit is not playing. If you want to force the contrast high, ground pin 3 of CN14 to enable you to evaluate the rest of the keyboard, and note any other faults. Roland very helpfully provide decent self test routines, as shown in the service manual. Regards. Kevin