IBM 6151 Maintenance And Service Manual page 181

Step 5
One of the options or adapters you removed is failing. Use the
following procedures to isolate the failures.
1. Set the power switch on the system unit to Off.
2. Install one of the removed options or adapters. Use the
following order, slots D, B; then the adapters in the other slots,
being sure that the fixed-disk and diskette drive adapter is the
last adapter installed. (You may want to install or attach more
than one at a time; then isolate to one.)
3. If the adapter has a device attached to it, be sure the device is
connected and the power switch on the device is set to On.
4. Set the power switch on the system unit to On and wait 2
minutes; then answer the following question.
IS "21," "22," or "23" DISPLAYED
IN THE
TWO-DIGIT
DISPLAY?
YES Repeat the above steps.
NO Go to "Step 27" on page 3-0060-29
(6/88) Problem Isolation Charts 3-0060-5