Bias
Remove the B +
fuse F2. This fuse is in the line from the
’ +’
c a p a c i t o r
terminal to hole # 3 on the board. Connect an
ammeter’s
'
+
'
!ead to the fuse clip nearest the large filter
capacitors. Connect the’
-’
lead to the other side of the fuse clip.
Avoid intermittent connections, and do not short the leads
together. Turn the amplifier on, and if possible adjust the line
voltage to 120 volts. Adjust P2, near the middle of the board, to
275 mA. Turn the amplifier off, and when the current drops to
zero, then remove the ammeter and replace the fuse.
Offset
A DC voltmeter capable of resolving 10 mV variations is
needed. Connect it to the output terminals of the selected chan-
nel, and adjust Pl, near the top of the board, to zero volts, + 10
mV. A small correction of the control will produce a large initial
change, which will settle
down
in a second. Repeat these small
changes to achieve zero volts.
SERVICE POLICY AND LIMITED WARRANTY
The DH-220 Power Amplifier has been carefully engineered
to provide many years of use without requiring any mainte-
nance or servicing.
Factory assembled units are subjected to several physical and
electrical tests before shipment. The output circuit board
assemblies of kit units are similarly tested prior to shipment. In
spite of all this testing,shipping damage does occur, kits are not
assembled properly or someone “goofs” and service and/or
maintenance will be required. The David Hafler Co. provides
complete service facilities at the factory to make any necessary
repairs.
It is the owner’s responsibility
to return or ship the unit freight
prepaid to the factory service department. Units shipped freight
collect will not be accepted. For units to be repaired under war-
ranty a copy of the dated bill of sale must accompany the unit.
Shipment should be via UNITED PARCEL SERVICE. Parcel
Post is not a safe way to ship electronic equipment. The factory
will not be responsible for damage caused by parcel post ship-
ment and repairs will be made at the owner’s expense. When
shipping your DH-220 be sure to insure it for the full value of an
assembled amplifier.
Use the original carton and packing material to ship your
amplifier. Enclose with the unit the following information:
1.
2.
3.
4.
5.
Complete shipping address (Post Office Box numbers are
often n o t acceptable.)
The serial number.
Copy of dated bill of sale if repairs are to be made under war-
ranty.
Description of the malfunction. If intermittent, please note.
We also suggest further identifying the unit as yours by put-
ting a label on the bottom or tieing a label with your name
and address on the line cord.
All service work is guaranteed for 90 days.
Warranties apply to the original purchaser only. Warranties
are void if: a) the amplifier has been either physically or elec-
trically abused or used for some purpose for which it was not
designed, or b) the amplifier has been modified without factory
authorization.
The transformer warranty is void if the leads have been cut
too short for reuse. If you think a transformer is defective the
leads must be unsoldered, not cut, for its return.
Technical assistance to help you locate the source of a prob-
lem may be obtained by calling the Technical Services Depart-
ment at 609-662-6084, 8 a.m.-4:30 p.m. E.T. It is helpful to
know the serial number of the unit and the results of any tests
you have performed.
SERVICING AN AMPLIFIER MODULE
If you are certain that the problem is confined to one of the
amplifier modules (comprising the circuit board, heat sink, and
output transistors), you may remove and return only the
module for service. Be sure that the components on the circuit
board are well protected - as by a surrounding sleeve of cor-
rugated cardboard which rests against the heat sink, and pro-
jects beyond the components. Properly packed and insured for
$150, this assembly can be sent by parcel post, as well as UPS, if
necessary. A service fee of $20 must be sent with every module,
since the fault may have been caused by a wiring error
elsewhere. For this reason, too, and because we have no control
over its proper reinstallation, the service warranty on a separate
module is limited to assurance of its proper functioning when it
leaves the service facility. All modules are tested before being
returned to you. If you believe the fault is the factory’s warranty
responsibility, include the serial number and the
bill of sale.
If in
our judgement the fault is entirely a manufacturing defect, a
portion of the service fee will be refunded. Only a complete
amplifier can be fully checked and given a service warranty.
WARRANTY FOR KIT-BUILT UNITS
The parts in a DH-220 kit are warranted for a full year from
the purchase date. If a defective component is found on a circuit
board or in a kit, simply return the
individual
part to the factory
prepaid together with the serial number and the date of pur-
chase, and it will be replaced at no charge.
If you cannot locate what is wrong with your DH-220, return it
to the factory with a copy of the dated bill of sale, and a check for
$40. If the sole cause of the problem is a defective part, the unit
will be repaired and returned to you transportation prepaid, and
your $40
less a charge for repackaging and shipping
will be
returned to you. If the problem is found to be an error in your
assembly of the amplifier, the amplifier will be put in proper
working order, tested to be sure it is meeting specifications, and
returned to you (freight prepaid within the continental U.S.). Ex-
cess shipping charges for expedited service, or overseas
delivery are your responsibility. At the sole discretion of the fac-
tory service department, if the time required for diagnosis,
repair and testing, and the nature of the malfunction warrants it,
a portion of the submitted repair fee may be rebated.
This warranty is void if the kit has not been completely
assembled or if other than rosin core solder has been used. Units
assembled with acid core solder or paste flux will be returned
unserviced.
WARRANTY FOR FACTORY ASSEMBLED UNITS
The DH-220 is warranted for three years from the purchase
date including parts and labor and normal shipping costs from
the factory to the owner within the continental U.S. The owner
is responsible for returning the unit to the factory and must sub-
mit a copy of the dated bill of sale.
This warranty gives you specific legal rights. You
have other rights which vary from state to state.
may also
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