Troubleshooting; Grounding, Noise, And Power Issues - Bosch ACS 561 Repair Instructions

ACS 561 Service Manual
Grounding, Noise, and Power
Issues
To provide proper protection and maximize
system reliability, it is important to consider
grounding, shielding, and AC and DC power
supply issues.
Grounding Issues
Grounding must be looked at first, for without a
low impedance ground; all of the noise protec-
tion measures built into the electronic compo-
nents and assemblies are rendered useless.
Grounding equipment is done for two reasons.
The first and most important is safety. To meet
safety requirements, any exposed conductive
surface of the equipment must be within the
safe touch voltage range of under 30 Volts
RMS. Any voltage greater may result in a life
threatening electrical shock if conditions are
met.
The second reason is the process by which the
case and any extensions of the case are con-
nected to earth ground. If the ground is open or
has a high resistance, electrical noise will not be
shorted to ground and can radiate into the unit.
Noise (Shielding) Issues
Proper shielding prevents noise from enter-
ing the unit. Two types of noise can affect the
operation of a unit; noise coming in on the AC
line and external noise (such as ignition noise)
radiated directly into the unit.
AC Noise - any signal on the power line other
than the advertised voltage and frequency; this
includes spikes, surges, and sags.
External Noise - (such as ignition noise) is
generally radiated into the unit. Other types of
radiated noise sources are light ballasts, trans-
mitting towers, power lines, etc. External noise
can cause the unit to lock-up, reset, or behave
erratically. The effect varies with the type and
intensity of the noise.
Robert Bosch GmbH

TROUBLESHOOTING

Power Issues
The power applied to the unit must be from a
stable, low impedance source. Long term stabil-
ity must be within +5% or –10% of the nominal
voltage. For a 230-Volt line the limits are 207V
to 241V. The unit will operate above and below
the voltage limits. However, problems in op-
eration may appear if the voltage drops (sags)
below or rises above (surges) these limits. The
life expectancy of the components in the unit
may be shortened significantly.
The impedance controls the ability of the line to
supply a constant voltage with a changing load.
Noting the line voltage with the unit off, then
noting the voltage with the unit on, a technician
can determine the impedance of the line from
the unit to the power transformer. If there is a
greater than 5% change, the line has too much
resistance or load is too great. The solution is
a dedicated line.
The line cord must be wired correctly. When
replacing the line cord, make sure the terminals
at the plug have high, neutral, and ground con-
nections in the proper locations. A ground circuit
tester can be used to test wiring.
Verify the Power Outlet
1. Ensure the outlet is in good working order.
2. With no load on the circuit, use a ground
3. Using a DVM and with no load on the circuit,
4. With no load on the circuit, verify the output
5. With the unit connected to the circuit (load-
6. Using an oscilloscope, monitor the wave-
31
Diagnostics and Testing
circuit tester to verify proper polarity and
presence of earth ground.
verify there is less than .3 Volts from neu-
tral to ground and the voltage is stable. Be
suspicious of a 0-Volt reading. This may in-
dicate a short between neutral and ground.
voltage is nominally 230 Volts and stable.
ed) verify the voltage varies less than 4 VAC
measured from neutral to ground.
form output from the outlet for any distortion.
The signal should be a sine wave.
SP00D00517 2018-07-11