IBM 3274 51C Maintenance Information page 299

F.3.6.5 PTX Amplifier Service Check (Figure F-38)
1. Power down.
I
DANGER
Voltage is still present at the socket when the power
cable is disconnected.
2. Disconnect the ac drive motor power cable
G.
3. Remove the PTX connector
G
from the control card.
4. Power up.
5. Connect the positive probe
G
of multimeter
G
(15 Vdc scale) to the index test pin TPE01 on the con-
trol card.
6. Connect the negative probe
G
of the multimeter of
TPB02 (ground).
7. Check the multimeter
CD
for a reading of less than
1 Vdc.
F-56
8. Install one end of jumper
e
to pin A04 of the PTXCP
socket on the control card.
9. Observe the multi meter , and touch the other end of the
jumper several times to pin A01 of the PTXCP socket
on the control card. The multimeter should read
2.5 Vdc or more when the test pin is touched. (A
wrong measurement can occur the first time the test pin
is touched.)
10. Repeat steps 8 and 9 with the jumper on pin A03 of the
PTXCP socket on the control card.
11. Power down.
12. Remove the jumper.
13. Reinstall the PTX connector on the control card.
14. Reconnect the drive motor power cable.
15. Power up.