Hafler DH-200 manual If Problems Arise

55 I Select the white pair of wires at the front of the chassis. Tuck the excess-wire into the corner and connect one wire to each of the lugs on the thermal breaker. Solder each.

56 [ Select the left output module, check it as before to see that underside connections near the holes are secure, and that the holes are visible. Place it against the left side of the chassis with the breaker at the front, board up.

57 : Prepare a 6” green wire. Connect one end to hole #lo.

(S). Be sure it cannot touch the transistor mounting screw! Connect the other end to FL lug #2. (S).

58 : Select the green and white pair from output terminals LB and LR. Connect the green wire to hole #7. (S). Con- nect the white wire to hole #5. (S).

59 I Select the white pair from LF. Connect the shorter wire to hole #8 (S). connect the other wire to hole #6 (S).

60 : Prepare a 5 1/2 white wire. Connect one end to hole 3.

(S). Connect the other end to FL lug #4. (S).

61 1 Select 4 sheet metal screws and fasten the module to the chassis, making sure no wires are trapped.

62 ! Select the green and white pair from input socket LS. Connect the green wire to the top rear hole #2. (S). Con- nect the white wire to hole #l. (S). Solder these on the back of the board.

63 I ! Tuck the excess of the remaining white pair of wires into the front corner, and connect one wire to each lug of the thermal breaker. Solder each.

64 : : Select the 7 ampere slo-bid fuse (a slo-bid fuse has distinc- tive internal construction) and install it in the single fuse clip FC.

65 C Select four 5 amp regular fuses, and install them in the dual fuse clips FL and FR.

66 0 Select the two 2 amp fuses, and install them in the twist type fuse holders on the back panel. These fuses will pro- vide reasonable protection for most speakers. See the Operation section of this manual for more detailed infor- mation. The remaining 5 amp fuses are alternates for the back panel holders for high power test purposes.

67 0 For lowest distortion performance and lowest noise, cor- rect placement of some wires is important. The wires from the output terminals and the back panel fuse holders should be kept against the chassis. The input socket pairs should be about an inch above the chassis, (the left pair can be tucked under the rear chassis lip), and should turn upwards at the bottom center of the cir- cuit board, about 1/2" to 1” off the board, in the plane defined by the edges of the finned heat sinks. The wires to the dual fuse clips should be kept away from the board and against the chassis, bringing the excess length for- ward of the fuses. The leads to the power supply capacitors should be kept away from the boards. The

green ground leads from the black output terminals and the ground lug should be brought together through most of their length.

68Check all your soldered connections - especially those on the fuse clip lugs, which are sometines difficult to solder to. Clip off any excess bare wire which could short to adjacent lugs or the chassis. Pay particular attention to the stranded wires from the transformer and line cord, and check the power switch connections. Now turn the amplifier upside down and shake out any bits of wire or solder.

69q Slide the cover in place, and install it with the eight sheet metal screws.

700 Remove the backing from the serial number label, and apply it to the bottom at the center rear. (This may have already been done at the factory.)

IF PROBLEMS ARISE

Each circuit module, which comprises all the “active” amplifier circuitry, has been incircuit tested to standards iden- tical to factory built amplifiers, prior to being packed in a kit. Thus, with careful assembly, the likelihood of a circuit fault is near zero. If you are certain the problem lies in the power amplifier, check the pilot lamp. If it is blinking, excessive temperature has shut down the amplifier. After a few minutes to cool, it will turn on automatically. If it soon shuts down again, and the amplifier has sufficient ventilation, the malfunction is either internal, or the result of an excessive (and very likely inaudible) input signal. In that case, the source must be investigated.

If the pilot lamp is not lighted, the main fuse in the single fuse clip near the power switch is probably open. If a replacement 7 ampere Slo-Blo fuse (do not use a larger value) also blows, the amplifier has a power supply problem, and requires profes- sional service.

If there is a problem in only one channel of the amplifier, that channel may be isolated by removing the power supply fuses in the adjacent dual fuse clip, and the other channel may be used monophonically. We do not encourage local service of this amplifier because some components may not be available lo- cally, and substitutions are not recommended at all. You may return a defective module for factory service. This reduces ship- ping weight and the likelihood of damage. To remove the module (leave the heat sink attached to the circuit board) tag each wire with the circuit board hole number as you unsolder it from the board, and insulate each bare wire end. It is safer to also remove the power supply fuses from that channel. The wires to the thermal breaker must be temporarily soldered together, and insulated.

Adjustments for Bias and DC Offset

These two potentiometers on each circuit board have been set at the factory and should not normally require adjustment for the life of the amplifier. In the event of repairs such as tran- sistor replacement, the following is the procedure, after remov- ing all input and output connections to the amplifier.

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