Thursday, December 10, 2015

INFINITY HPS 250 Powered subwoofer disassembling bias adjustment and test procedure

INFINITY HPS 250 


Bias Test
1. Remove and expose amplifier assembly by following instructions above. All connectors must remain intact.
2. Locate and disconnect the CD+ connector on the main board; insert a DC Ammeter set to a low range between the connectors.
3. Locate and adjust R13 and R28 potentiometers on the main board near the connector to maximum CCW.
4. Connect power cord, turn on power switch; verify initial DC current is less than 1.5mA.
5. Adjust R28 CW slowly until meter reads 5 mA.
6. Now adjust R13 CW slowly until meter reads 10 mA.
7. Turn power OFF; disconnect Ammeter and re-connect CD+ terminal.
Audio Test
1. Remove the woofer by following instructions above; replace with a 20 ohm 100 watt resistive load.
2. Connect a voltmeter and oscilloscope to the amplifier output terminals, plus the load.
3. Adjust the Gain control to minimum. Frequency should be set to maximum. (Phase is irrelevant); there is no input signal for this test.
4. Turn on the unit; Observe voltage on oscilloscope and rotate controls; AC noise should be less than 8 mV.
5. Adjust the Gain control to minimum; Frequency should be set to maximum. (Phase is irrelevant) Connect a signal generator to the Left Low Level (RCA) input; only one cable is necessary; set the generator to 60Hz, 800mV.

Note: A high gain amplifier of at least a 100 watt rating is recommended for this test)


General Function
UUT = Unit Under Test
1. Connect both right and left line level inputs (RCA) to signal generator and UUT. Use Y-cable if necessary from mono source. GAIN control should be full counterclockwise.
2. Turn on generator, adjust to 100mV, 50 Hz.
3. Plug in power cord to UUT; push the main AC power button ON. Green LED should be lit.
4. Turn GAIN control full clockwise; immediate bass response should be heard and felt from port tube opening.
5. Turn off generator, turn GAIN control fully counterclockwise, and disconnect RCA cables.
6. Connect one pair of speaker cables to either pair (R) or (L) input terminal on UUT. Cables should be connected to an integrated amplifier fed by the signal generator.
7. Turn on generator and adjust so that speaker level output is 2.0V, 50 Hz.
8. Turn GAIN control full clockwise; immediate bass response should be heard and felt from the port tube opening.
Sweep Function
1. Follow steps 1-4 above, using a sweep generator as a signal source.
2. Sweep generator from 20Hz to 300Hz. Listen to the cabinet and drivers for any rattles, clicks, buzzes or any other noises. If any unusual noises are heard, remove driver and test.
Driver Function
1. Remove driver from cabinet following instructions on page 5.
2. Check DC resistance of driver; it should be 21 ohms +/-10%.
3. Connect a pair of speaker cables to driver terminals. Cables should be connected to an integrated amplifier fed by
a signal generator. Turn on generator and adjust so that speaker level output is 30.0V.
4. Sweep generator from 20Hz to 1kHz. Listen to driver for any rubbing, buzzing, or other unusual noises. 

DISASSEMBLY PROCEDURES
Amplifier Removal
1. Lay the subwoofer on its side on a padded surface, amplifier facing upwards.
2. Locate and remove the (2) Allen head screws (#2) at the bottom of the plastic cover with a 3/32” wrench.
3. Slide the amplifier straight down until it clears the slotted brackets (#4) & (#5); pull away from the cabinet and expose for servicing without further disconnection.
4. To remove individual boards if desired, remove Philips screws and all relevant molex or other connectors.
5. Wires threading through the cabinet, glued in place, should be left intact under all circumstances.
Woofer Removal
1. DO NOT ATTEMPT TO PRY THE GRILLE (#10) OUT OF ITS RECESS.
2. Lay the subwoofer on its side on a padded surface.
3. Remove the (4) rubber foot plugs (#15).
4. Remove the (4) 1” foot screws (#16), remove all four feet.
5. Remove all (8) 2” expose bottom panel screws (#13).
6. Pull the bottom panel (#12) out of the cabinet - one way to accomplish this is to partially screw one of the 2” screws back into a threaded “foot” hole and pull on the screw. Lift the bottom panel & woofer (#9) out of the cabinet.
7. Unplug both woofer terminals; remove all (8) 3/4” screws (#11).
WHEN SERVICING THIS AMPLIFIER:
1. Do not touch the metal frame of the woofer (if removed from the cabinet) when driving the amplifier at high power levels. In the unlikely event that the output devices in the amplifier fail and present an open circuit during their operation, AND the driver voice coil was to come in contact with the motor assembly, hazardous voltage could be present at the woofer frame.
2. When 120/230v-based test equipment is connected to the amplifier in any way, use of a 1000W isolation transformer on the subwoofer is necessary for safety; in addition, an isolator plug, (a three-to-one pin adapter sometimes called a “cheater plug”) should be used on the power cord plug of the test equipment being used.
POWER AMPLIFIER CIRCUIT DIAGRAM 
CLICK ON THE IMAGE TO ZOOM IN