HK hk1901 schematic
FM 049
Service Bulletin Letter
Affected products:
HK Audio DART
Change released: 26-Aug-02 Bulletin letter no.: HK0004-0
Internal project code: HK1901
Affected serial no.: from to
Changes already implemented by manufacturer from serial no. 20043286 on-
wards
Symptoms:
mains fuse open, current limiting relay Rel2 does not switch on or unit does
not work at all due to disruption of NTC R115
Reasons:
wrong value (3,3kohms) assembled for resistor R2;
of that reason relay Rel2 does not work and NTC R115, which is working as
transformer inrush current limiter, is remaining in the primary circuit instead
of getting shorted after a short delaytime by the relay contacts.
This failure is not obvious and the unit is working normal due to the NTC's
value is decreased to a few ohms while becoming hot. But there is a substantial hazard, that the NTC will be damaged soon, when working under permanent
load.
Remark: even when the unit is correctly assembled and working well, it may
happen that the mains fuse will be destroyed, when the unit is switched on and
off a few times in very short intervalls.
Reason: the NTC can not cool down fast enough and is remaining hot . Under
this condition the NTC has only a few ohms and is not able to limit the inrush
current of the transformer, which leads to a destroyed mains fuse.
Measures:
replace R2 with 1kohms/ 0.25W resistor, or
replace R2 with 1kohms/ 0.25W resistor and fuse, or
replace R2 with 1kohms/ 0,25W and defective NTC R115
Photos/ schematics
See next page
Seite 1 / 2
Dart service bulletin HK1901.doc QS Stand A, 14.09.06
FM 049
Service Bulletin Letter
Seite 2 / 2
Dart service bulletin HK1901.doc QS Stand A, 14.09.06
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