PT-VW350, PT-VW350D, PT-VW350T, PT-VX420, PT-VX420D, PT-VX420T, PT-VX421 (serv.man4) - Panasonic Projector Service Manual (repair manual). Page 4

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1. Safety Precautions
1.1. General Guidelines
  - For continued safety, no modification of any circuit must be attempted.
  - Unplug the power cord from the power outlet before disassembling this projector.
  - Use correctly the supplied power cord and must ground it.
  - It is advisable to use an isolation transformer in the AC power line before the service.
  -  Be careful not to touch the rotation part (cooling fan, etc.) of this projector when you service with the upper case removed 
and the power supply turned ON.
  -  Observe the original lead dress during the service. If a short circuit is found, replace all the parts overheated or damaged 
by the short circuit.
  -  After the service, all the protective devices such as insulation barriers, insulation papers, shields, and isolation R-C combi-
nations must be properly installed.
  - After the service, check the leakage current to prevent the customer from getting an electric shock.
1.2. Leakage Current Check
  1. Prepare the measuring circuit as shown in Fig.1.
Be sure to use a voltmeter having the performance described in Table 1.
  2. Assemble the circuit as shown in Fig. 2. Plug the power cord in a power outlet.
  3. Connect M1 to T1 according to Fig. 2 and measure the voltage.
  4. Change the connection of M1 from T1 to T2 and measure the voltage again.
  5.  The voltmeter must read 0.375 V or lower in both of steps 3 and 4. This means that the current must be 0.75mA or  less.
  6.  If the reading is out of the above standard, the projector must be repaired and rechecked before returning to the customer 
because of a possibility of an electric shock.
10KΩ ±0.1%
(V) V
Rs: 1500 Ω±0.1%
Cs: 0.22 µF±1.0%
Rb: 500 Ω±0.1%
to T1
or T2
in FIg.2
Weighted leakage current=Vb / 500 (A)
Fig. 1
Isolation transformer
to power outlet
Circuit (Fig.1)
(rms reading)
≤ 2%
Input resistance: 
≥ 1 MΩ
Input capacitance:  ≤ 200 pF
Frequency range:  15 Hz to 1 MHz
Table. 1
1.3. UV Precaution and UHM Lamp Precautions
  - Be sure to unplug the power cord from the power outlet when replacing the lamp.
  -  Because the lamp reaches a very high temperature during its operation, wait until it cools completely when replacing the 
Lamp Unit.
  -  The lamp emits small amounts of UV-radiation, avoid direct-eye contact with the light.
  -  The lamp unit has high internal pressure. If improperly handled, explosion might result.
  - Because the high pressure lamp involves a risk of failure, never touch the lamp wire lead during the service.
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