IBM System/370 145 Reference Summary page 112

START LINE TIPS
Start Imes are a low-cost and low-noise method of starting regulators
1n
a
controlled sequential manner as compared
in
the past to separates DC-
controlled contactors which are noisy and costly It
ts
important for
customer engineers to know how to manipulate regulators when problems
occur
Typical Normal Running
Reg 5 Voltage Across
CPU
MSF
Start Line
MST Dual
Start Lines are ES-El 1* 101,102, 201 05v
103, 104,
MST Single
Lever +7v,+6vare E12-E14 106, 108, 202 05v
402,401
Phase Control
Regs +2v are E8-03A2 D08 110, 111, 207,208, Open
112,405,
205,206
406 407
Phase Control
Regs+l 25/-3are E8*-03A2 008403,404 .05v
* Short to ground (AC Frame) to turn on
Pull any E8 sllpon connector off to turn on a +2v supply.
Do not short to ground, but put a
JUmper
between E12 and E14.
Float about seven volts above ground.
11 - 13vdc
If DC d15tr1butor, DC bulk input (MST regs El and E2) and DC bias
18-20vdc are all present. Then 1f a problem exists it will usually show up
as an improper start signal
SYSTEM CHECK LIST
Troubleshooting Action
DC Voltage At Gate
If no voltage is present from a regulator:
Check the wiring, especially the sense leads.
Check for bulk voltage at regulator terminals E1 and E2.
Check for bias voltage at regulator.
With an oscilloscope, check for an output increasing
then turning off, indicating either an overcurrent or
an overvoltage. An overcurrent usually indicates a
problem in the system, not in the regulator. An over-
voltage usually indicates a bad regulator.
Since the regulators are somewhat dependent on each
other, a problem on one can cause an overcurrent or
an overvoltage on another.
It
is important to find the problem that occurred first.
AC Ripple Voltage At Gate
If the ripple voltage is greater than the values listed, the
regulator is probably oscillating. This can be caused by:
Wrong sense load connection at the gate.
Bad sense caps at the gate.
Another regulator could also be oscillating.
A bad regulator itself.
AC Ripple Frequency At Gate
If there is any ripple voltage at the gate, it should have a
frequency of 2.4kHz. If it is about 1mHz or higher along
with a high ripple voltage, the regulator could be oscil-
lating. Refer to the preceding step.
AC Ripple Voltage At Bulk: E1 to E2 at Regulator
If the ripple voltage is greater than the values listed, a regu-
lator could be oscillating. (The bad regulator could be on
another transformer). Voltage peaks should be within
0.2v of each other.
AC Ripple Frequency At Bulk: E1 to E2 at Regulator
Voltage peaks should be 0.4 milliseconds apart (2.4kHz)
if one peak is missing a diode could be bad.
Remote Start Noise (DC) At Regulator
When the system is running, the DC voltage shift including
noise spikes should be less than 150mv. If this is too
high, check the sequencing circuitry.
DC Start-Up Voltage At Gate
The + 7v, 1 .25v, and -3v for the memory have control led
start up ramp voltages. If they have input power but no
start signal, the output voltages are:
+ 7v is approximately +1.5vdc.
+1.25v is approximately 0.35vdc.
-3v
is approximately -0.6vdc.
DC Start-Up Voltage At Remote Start Points
At Regulator
Without the start signal, the remote start points at the
regulator will be between +4v to +16v. When the start
line closes, the voltage should go to overvoltage. Refer to
"Remote Start Noise (DC At Regulator)."
Sense Point Noise Shots
In some systems, noise shots have been seen when equip-
ment such as typewriters are turned on. In some cases,
these noise shots have fired the overvoltage circuits in a
regulator, turning it off.
AC Input Current Waveform Symmetry OCR
Refer to "Procedure For Isolating The Improper SCR
Firing Sequence Condition On 2v-250A Regulator."
AC Input Current Balance
Refer to the preceding step.
OCR Reset Pulse
Refer to 2v (250A and 290A) Reset Pulse Adjustment.
There is no adjust for the OCR Dual.
OCR Gate Pulse
The gate pulse for all OCRs is approximately 12 micro-
seconds wide with an amplitude of three to five volts.
The pulses should occur every 0.4 milliseconds. The
pulses should be stable and have no ringing or extra pulses.
Overvoltage Levels
The overvoltage levels are listed so it can be determined
if a regulator went over voltage and activated its protection
circuit.
9.10