Kurzweil PC88 - Page 84

Chapter 4 Troubleshooting
Power Switch
1. To check the power switch, turn the power switch
to the "off" position.
2. Place one probe at the center contact of AC
receptacle and the second probe at the second pin
from the right of the bridge rectifier, D14. You
should read in excess of 9 Volts.
3. Turn the power switch to the "on" position.
Measuring the same points, you should read
approximately 0 Volts.
4. The power switch is functional.
Power Supply Voltage Regulators
1. Disconnect the power cable, PC-1, at Location J302.
2. Seta DVM to DC, 20 Volts. With negative probe to
ground, check VR1 (+5VMASS), first pin to the
right you should read approximately 5 Volts.
Perform the same for VR2 (+5VDIG) and for VR3
(+5VANA).
3. If any measure low, perform the same as above on
the third pin from the right. You should read 10
Volts or excess on all three.
4. If any read low, connect an oscilloscope to that pin
and see if you have excessive AC ripple, which
would indicate a bad input smoothing cap, C28 or a
bad bridge rectifier, D14 (open).
5. If the DC value is 10 Volts or greater and the
output is still low, but there is no excessive heating
on VR1, VR2 or VR3; replace VR1 and/or VR2.
6. For VR3 check C8 for a short or low resistance
reading. If it is short or low, replace C8. If C8
measures correctly, replace VR3.
PC88 Service Manual
4-4