B&K Precision 1249B - Manual - Manual (Page 40)

40
TEST INSTRUMENT SAFETY (CONT.)
(continued from inside front cover)
7. Testing "hot chassis" video-equipment is especially hazardous unless the proper safety precautions are taken. Most recent television
receivers and other equipment with a two-wire ac power cord are the “hot chassis" type: this even includes many with polarized power
plugs. A plastic or wooden cabinet usually insulates the chassis to protect the customer but when the cabinet is removed for servicing there
is great danger of serious electrical shock if the chassis is touched. To prevent electrical shock, always connect an isolation transformer
between the ac outlet and any hot chassis equipment under test. The B+K Precision Model 1604A or TR-110 Isolation Transformer, or
Model 1653A or 1655A AC Power Supply is suitable for most applications. To be on the safe side, treat all two-wire ac powered
equipment as "hot chassis" unless you are sure it has an isolated chassis or an earth ground chassis. Use of an isolation transformer has no
disadvantage, even if it is not required.
8.
In addition to the hot chassis shock hazard mentioned in Item 7, severe damage to test instruments or the equipment being tested is
probable from connecting a cable between the NTSC Generator and any "hot chassis" equipment unless an isolation transformer is used.
The antenna terminals of a hot chassis set should already be isolated from the chassis, unless defective, and the isolation transformer may
not be required. For connection to any other point, an isolation transformer is needed.
9.
Capacitive coupled outputs of the Model 1249B NTSC Generator are rated at ±35 volts (DC + AC peak) maximum: this includes the
IF/RF and COMPOSITE VIDEO jack. All other input and output jacks are direct coupled and are rated at ±5 volts (DC + AC peak)
maximum. Make test connections at circuit points which do not exceed this value. If in doubt, first make voltage measurement with
voltmeter or oscilloscope. Connection to higher voltage may damage the equipment.
10. When testing any ac powered equipment, remember that ac line voltage is usually present on some power input circuits such as the on-
off switch, fuses, power transformer, etc. any time the equipment is connected to an ac outlet, even if the equipment is turned off.
11. Servicing of this unit should be performed only by qualified electronics technicians who are trained to work safely in the presence of high
voltage.
12. Never work alone. Someone should be nearby to render aid if necessary. Training in CPR (cardio-pulmonary resuscitation) first aid is
highly recommended.