Zenith CM-150 Series Service Manual

Contents

Zenith CM-150 Series Service Manual Manual pdf 23 page image

CM150/PV150 3-1 GM CHASSISTROUBLESHOOTINGTROUBLESHOOTING THE GM TELEVISION SYSTEMA system is easier to troubleshoot when broken downinto circuit groups. A blank display with no audio doesnot necessarily mean you are working with a dead set.Make adjustments after you isolate the problem. Do notstart troubleshooting by turning pots or using otherservice controls.Start your checks by verifying the status of standbyconditions, power on start conditions, sweep startconditions, and then check video and audio systemconditions. The most basic test aids to use, if the set hassweep and audio (controllable noise), are the menus anda VCR. If there is no sweep or high voltage, then youmust make some measurements to isolate the cause toan area of the system.It is recommended that you perform troubleshooting inthis order: power supplies, horizontal sweep/highvoltage, vertical sweep, video, and audio.The list of service checks on the following pages takesyou from standby to power and sweep on conditions.Where possible, you have been given both DMM (digitalmulti-meter) readings and oscilloscope observations forthe active signal checks.For most active signal checks and DC voltage measure-ments, use the right end of RX3401 in direct viewproducts and the left end of RX3401 in projectionproducts for the DC common side of your meter orscope. To take meter readings on the primary side of theswitch mode power supply, use front lead of RX3437 indirect view products and the jumper W-3 in projectionproducts for the meter AC common.If the audio 26VSW (connector 3K9) is missing, you mayhave partial or distorted audio. The audio system ispowered by supplying 15VSB to the audio poweramplifiers, via Q4001 and Q4002, during power on untilthe audio 26VSW turns on. 15VSW is supplied to IC800and IC850 via CR801 and CR850, which prevents audionoise during power on. When the audio 26V is present,CR801 and CR850 back bias, preventing the 15VSW and26V from mixing. CX848 and CX856 are kept charged toprevent audio noise during power off.15VDCTL15V SBPW R CTRL12V SW37V SBYPW R FAGNDGND1881<15.5V><0V><0V><37.7V>Not Used(15V)(4.2V)(11.8V)(37.4V)(37.4V)<37.7V>MAINMODULEPW R SUPPLYSW EEPMODULE2N3-2 3N2-2 3G2-22G3-3HORZ DRVVERT DRV3.5V p-p or 1.5V rms4.0V p-p or< > = STBY ( ) = PW R ONA Line GM Chassis Power ControlDirectview6A33A6