YORKVILLE ap4020 ys4020 Service Manual

Also see for ap4020 ys4020: Service manual Owner's manual

Contents

SERVICE BULLETIN SERVICE BULLETINw w w . y o r k v i l l e . c o mREAL Gear.REAL People.Yorkville Sound550 Granite CourtPickering, OntarioL1W-3Y8 CANADACanadaVoice: (905) 837-8481Fax: (905) 837-8746Yorkville Sound Inc.4625 Witmer Industrial EstateNiagara Falls, New York14305 USAU.S.A.Voice: (716) 297-2920Fax: (716) 297-3689w w w . y o r k v i l l e . c o mREAL Gear.REAL People.Yorkville Sound550 Granite CourtPickering, OntarioL1W-3Y8 CANADACanadaVoice: (905) 837-8481Fax: (905) 837-8746Yorkville Sound Inc.4625 Witmer Industrial EstateNiagara Falls, New York14305 USAU.S.A.Voice: (716) 297-2920Fax: (716) 297-36892 2STEP 6. Measure across the pair of test points shown in the componentlayout listed in the table below. If the measured value is notwithin + or – 10% of the value listed in the table then replacethe resistors shown in the table below.STEP 7. Measure the resistors coloured ORANGE. Since the value ofthese resistors is 0.1 ohm, your ohmmeter will measure thehigher series resistance of the test leads if the resistor is OK. Ifthe resistor is damaged your ohmmeter will read a very highresistance (an open circuit). Replace any damaged resistors.STEP 8. Measure the output TO–3 transistors (Q13 to Q28) to deter-mine if any are damaged. Mark any damaged transistors witha marking pen.STEP 9. Replace any output transistors that you have marked as beingdamaged. Replace any diodes that you have found to be dam-aged. Replace all of the red transistors that were removed.STEP 10. Inspect the traces on the circuit board for any that have ‘fused’open or looklike they got very hot. Bridge and solder a piece ofwire over any damaged traces.Testing Repaired Circuit BoardsNow that you have rebuilt the M1146 or M1126 circuit board. It is just asimportant to properly power up the board. If the sinewave doesn’t look rightcheck the signal at test point (1) to ensure that the voltage amplifier isn’t dis-torting the signal. If there is still a damaged part on the board instantly turn-ing it on could blow up the board and you would be back where you started.Connect the power wires and ground to the power supply. Connect a digi-tal multimeter to test pins 8 and 9 to measure the bias quiescent currentand place a scope probe on the speaker output. Be sure to turn the quies-cent current trimpot RT1 fully counter clockwise.Now using a variac slowly turn up the AC main voltage while monitoringthe quiescent voltage and the speaker output trace on the scope. Watchingthese two test points is a good indicator of the health of the board. If youhave a second multimeter connect it up from the speaker output to testpoint 4 or 5. As you variac up also check these DC battery voltages toensure that they both increase in voltage to approximately +12 or –12 vdc.If the board looks OK after variacing up to 120vac then slowly turn up thebias (RT1 trimpot) to obtain 3 to 5 millivolts of bias voltage on test points 8and 9. Check the speaker output with a 1KHZ sinewave with no load. If thislooks good place the minimum rated load (4 Ohm for M1126, 2 Ohm forM1146) on the speaker output and increase the sinewave amplitude to thepoint of clipping. If the signal looks free of oscillation, place a short acrossthe speaker posts. The amplifier should go into protect mode after 1/10 of asecond. Remove the short and the sinewave will appear 6 seconds later.Reassemble the complete amplifier and run just clipping music or pinknoise into the minimum rated speaker load for that model of amplifier. Letthe amplifier heat up for 20 minutes. This will check the thermal mounting ofthe transistors and for any weak parts not caught during troubleshooting.TESTPOINTSR10LAYOUTREFERENCE4K7LAYOUTREFERENCER11, R12, R14CORRECTMEASURED VALUE-10%15ohm 17ohm+10%19ohmAP4020 &AP4040AP4020 &AP4040AFTER YOU HAVE REPLACED ALL OF THE NECESSARY COMPONENTS INSPECTTHE REPAIRED BOARD FOR ANY MISSING PARTS, CORRECT VALUES IN THE COR-RECT POSITION AND THAT ALL COMPONENTS ARE SOLDERED.If the amplifier passes this test the product is ready toreturn to the customer.