Kurzweil PC88 - Page 30

Chapter
2
Diagnostics
VGM Port Test
The VGM Port Test checks for the presence of a VGM
board by sending an Identity Request message. If a VGM
board is installed it will send back an appropriate Identity
Response message. If the expected data does not come
back, the test fails (i.e. no VGM Board installed).
If a VGM board is present and operational, the test uses
it to produce 5 sine waves. After each sine wave, press
any button (or keyboard key) to advance to the next one.
This allows the operator to take measurements before
continuing with the next step.
However, in the Burn-In Mode, a 5 second delay is
inserted between each tone.
The expected amplitude and frequencies are as follows:
SV P-P at 55Hz.
5.5V P-P at 220Hz.
SV P-P at 880Hz.
5.5V P-P at 1.5KHz.
5V P-P at 3.52KHz.
aac a a
A failure of this test indicates that:
1) VGM board is not installed,
2) the VGM Board is not properly functioning,
or
3) one of the signal paths to or from the VGM
connector is damaged. Note that, if the VGM
send and receive lines are improperly shorted
on the Engine Board, this test can pass falsely.
PC88 Service Manual
2-12