National NN-V680W, Service Manual

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1. How to check power transistors (Q701, Q702). To measure,
suck a solder from its legs completely unless faulse reading
may observe and mislead a troubleshooting. Measure
across pins between E-C, E-G, C-G, E-black lead, C-red
lead of tester should be infinite and may have some reading
in reverse, it is normal. Refer to attached table for normal
reading.
2. DB701 Diode Bridge
3. C704, C705 High voltage Capacitors. D702 and C705,
D701 and C704 are parallel connected therefore, remove
component to measure when diode is shorted.
4. D701, D702 High voltage Diodes
4. How to replace power transistors Q701, Q702 and Bridge
Diode DB701.
1. To remove Q701, Q702 and DB701 unsolder their legs first,
next remove a screw that holding the heatsink onto the PCB
then dtach the heatsink as shown below.
Service Hints: For easy solder removal, use one soldering
iron to heat a solder and use solder sucker iron to suck
solder.
2. Make sure to replace both Q701 and Q702 at a time with
the same maker.
3. Make sure to apply heat conduction grease between
transistor and heat sink.
4. NO DUST SHOULD CAUGHT between heat sink and
power transistor unless if causes looseness of heat
conduction and insufficient cooling to blow components.
5. Screw must be tighten securely.
6. Install the heatsink onto the PCB by a screw and make
sure to apply extra solder between legs and PCB pattern
so that it's able to flow 15A or more main current.
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NN-V690P / NN-V690PS / NN-V680W / NN-V680W