Zenith ZVM-121, Service Manual

Page 1: ...CopyrIght 1981 Zenith Data Systems All Rights Reserved SM ZVM 121 Video Monitor Service Manual NI Hldata systems SAINT JOSEPH MICHIGAN 49085 585 2 First Printing Printed in the United States of America ...

Page 2: ...ety Servicing Guidelines 1 1 Troubleshooting Guide 6 1 Specifications 2 1 Replacement Parts List 7 1 Controls 3 1 Semiconductor Identification 8 1 Disassembly 4 1 Circuit Board X Ray View 9 1 Circuit Description 5 1 Schematic 10 1 ...

Page 3: ...he board in place It slides into slots which are molded into the cabinet and the cabinet back holds it in place SAFETY CHECKS After the original service problem has been corrected check for the following FIRE SHOCK HAZARD 1 Be sure that all components are positioned in such a way to avoid the possibility of adjacent component shorts This is especially important on those chassis which are transport...

Page 4: ...D _63_ _1 04 0 1_ 7_6 SUCH AS WATER PIPE 1500Q CONDU IT ETC 10 WATT Figure 1 1 IMPLOSION PROTECTION 1 All Zenith picture tubes are equipped with an integral implosion protection system but be careful to avoid damage during installation Avoid scratching the tube 2 Use only Zenith replacement tubes X RADIATION PLACE TH I S PRO BE ON EACH EXPOSED METALLIC PART tube does not emit X rays when the HV is...

Page 5: ...age rectifier vacuum tube should have that tube replaced only with a Zenith recommended replacement type or a Zenith recommended solid state rectifier replacement The high voltage compartment and all metal shields where used must be kept in place whenever the chassis is operating If a shield is missing it should be replaced at once as a standard servicing procedure Page 1 3 TIPS ON PROPER INSTALLA...

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Page 7: ...minal Power Operating Current Nominal High Voltage Power Transformer Band Width Rise Time Screen Phospher Character Type 12MB15X 120 VAC 12 VDC 4 0 amperes std 28 watts 0 3 amperes 12 0 kV Standard 15 MHz 50 nanoseconds 12 diagonal P31j green 8 x 10 matrix Page 2 1 ...

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Page 9: ...ecessary to disconnect the wires on the outside terminals I CONTRAST CONTROL R203 This 1 kfl potentiometer is secured to a mounting bracket by two twist tabs To remove the control remove the bracket from inside of the cabinet Then remove the control knob and with a pair of pliers turn the two twist tabs to free the control See Figure 3 1 Adjustment Adjust this control for a screen that is comforta...

Page 10: ...11 40f80 J I RACTER CWI tf 1111111111 VERTICAL HOLD Figure 3 2 VERTICAL HOLD R612 This 250 kfl potentiometer is soldered to the rear of the chassis PC board See Figure 3 2 Adjustment If the picture rolls upward or down ward adjust the vertical hold control Turn the con trol clockwise or counterclockwise until the rolling stops Test Test this control by removing it from the cir cuit board Place an ...

Page 11: ... out the two rivets See Figure 3 2 Adjustment Use this switch to select 40 or 80 characters per line Page 3 3 Test To check the switch place the ohmmeter across the terminals The 40 character position will indicate zero ohms The 80 character position will indicate 1 ohms In the 80 character position the switch is open The meter is reading the resistance of L503 WIDTH CONTROL The width control is s...

Page 12: ...age at R709 See Figure 3 3 TheB voltage should be set at 12 7 VDC This 10 k l potentiometer is soldered to the left hand side of the chassis PC board See Figure 3 3 B ADJUST R7091 T 1 J VERTICAL VERTICAL HORIZONTAL SIZE HOLD HOLD Figure 3 3 CRT CONNECTOR ...

Page 13: ... remove the two screws that se cure the PC board to the switch bracket accessible LLLLLLlLLL LLLLLLLLLL PC BOARD SCREW I from inside the rear cover From the outside of the rear cover remove the one screw holding the charac ter switch bracket See Figure 4 1 Slide the switch bracket through the cabinet opening CHASSIS PC BOARD REMOVAL After you remove the cabinet you can remove the chassis PC board ...

Page 14: ... anode from the CRT GROUND CONNECTIONS 3 Remove the four screws one at each corner of the CRT The lower left hand screw has all the ground connections and grounding strap Be sure all the connections are in place after reas sembly 4 Loosen the screw on the yoke and slide the yoke off the CRT 5 Carefully lift out the CRT CAUTION Serious injury may occur if you should drop the CRT CRT PIN SOCKET ANOD...

Page 15: ... Schematic Diagram while you read the following information The signal flow from input to output is shown in the Block Diagram Figure 5 1 HOR IZ PROCESSOR VERT AMP II POWER SUP PL Y Figure 5 1 B VIDEO OUTPUT BEAM CURRENT LIM ITER Page 5 1 CRT HORIZ OUTPUT HOR IZ DRIVER ...

Page 16: ...oportionally This current is amplified by Q702 and fed to control transistor QX703 If the output voltage tries to rise Q701 will try to turn off causing Q702 and Q703 to turn off Conversely when the output voltage drops Q701 turns on harder turning onQ702 and Q703 and raising the output voltage back to nor mal A unique feature of this circuit is its ability to switch from a regulator to an active ...

Page 17: ...ircuit of QB05 a sync tip clamp consisting of CRB04 RB14 RB15 and RB20 is used to clamp the video signal so there are no black level shifts with variation in input signal OB05 2 RB04 RB03 220 2 2K B 12 4V SYNC AMP Figure 5 4 The video signal at the emitter of video driver QB05 is sent to the video output through the contrast control It is also sent to the base of sync amplifier QB01 The sync ampli...

Page 18: ...0 DC cou pling Because this circuit will not limit the maximum beam current at a sufficiently low value diode CR802 is required Diode CR802 is biased off until the beam current reaches 210 microamps At this point the diode is allowed to conduct The emit ter impedance is lowered considerably which in creases the collector current This limits the maximum beam current C814 0027 500V R827 15K hW 10 B ...

Page 19: ...ltage high This keeps the CRT biased off preventing spot burn B 110V R832 5 1K W L802 150uH CR803 R831 5 1K I2W C 9 1 160V R829 1 5K I2W 10 Q804 VIDEO OUTPUT C814 0027 r YELLOW 2 Figure 5 6 B 110V R827 15K I2W 10 1 5 YEUBLUE J I I J I I I 6 R207 7 YEL ORG 33K I W 10 R838 t20K R839 15K Page 5 5 TO N V ...

Page 20: ...60B discharges linearly through its resis tor network because this network is returned to yoke current sensing resistor R624 where a ramp voltage appears of the same amplitude as the ramp voltage across C60B A constant voltage appears across the discharge resistor and maintains the constant dis charge current from C60B Capacitor C60B provides a linear negative going ramp voltage of average DC valu...

Page 21: ...RRENT LIMITER R810 3 3K B 12 4V ____f N ___ t C807 R819 18K R824 2 4K 2 C813 820PF R836 10 R837 270 2 C505 10 16V tfl R507 27 R822 4 7K CR802 R515 120 10 16V TO PIN 6 IC501 B 12 4V Figure 5 7 Page 5 7 B 110V I C814 0027 r YELLOW 2 R827 15K hW 10 I E202 L1 E203 PIN 6 HORIZ SWEEP D 8t 16 iII R830 0027 33K hW 10 R838 120K R839 15K B 300 R818 180K R841 r RED I R824 2 7 I 133 MEG I hW IR2g4 t M E VG _ ...

Page 22: ...is the RC type with pin 7 being the control point The timing capacitor is charged up by an external resistor to a trip voltage set in the inte grated circuit When this trip voltage is reached the capacitor is discharged to a new trip value This pro cess is repeated producing a sawtooth waveform The output of the phase detector controls the oscil lator through resistive coupling from pin 5 to pin 7...

Page 23: ...6 CS02 1S0K 022 CS03 r 022 4 3 2 B 12 4V 7 IC501 RS02 RS10 2 2K 1S0K S 6 8 1 TODRIVER R506 15 10K CS07 01 CRS07 CS06 I TO R507 SOV R505 R517 C B 100K 15K R514 R513 R509 R508 2 2K 16K 33K 33K R525 tCW 1 2 MEG R519 R518 3K 100K HORIZ RS16 RS12 R511 HOLD E 1 SK 16K 33K RS20 100K C508 I 00S6 Figure 5 8 ...

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Page 25: ...ck the B at pin 6 It should be 8 9 volts If the regulator is defective the voltage drops VERTICAL SWEEP 1 Small vertical height R624 value may be too high 2 Picture deflected up C614 may be leaky 3 Vertical fold over C618 C617 or Q607 may be open 4 R631 and R632 will overheat if Q618 Q617 or Q607 are shorted 5 Top half of picture lost R622 or R623 may be open 6 Increase dissipation in Q603 and R62...

Page 26: ...2 o 0806 VIDEO PRE AMP o Q805 VIDEO DR IVER 0 0801 SYNC DRIVER R61 VERT HOLD 0 0607 CONTROL VERT BLANK O 0802 SYNC SEP 0604 0 0 VERT OUTPUT 1 0606 VERT O 0804 VIDEO OUTPUT OUTPUT 2 R51 O 0803 BEAM CURRENT IC50 r 1 LIMITER HORIZ J HOR IZ HOLD COLLECTOR OF TRANSISTOR PROCESSOR O Q501 HORIZ DRIVER L J 0502 HOR IZ OUTPUT Component Location for Chassis PC Board Figure 6 1 ...

Page 27: ...22 08 33 kn 5 film 1 4 W C604 22 7613 08A 470 pF 10 disc 50 V R509 63 9922 08 33 kil 5 film 1 4 W C606 22 7547 1 p F 10 polyester 50 V R510 63 9922 24 150 kil 5 film 1 4 W C607 22 7151 Q4 10 p F 100 10 elect 16 V R511 63 9922 08 33 kil 5 film 1 4 W C608 22 7547 1p F 10 polyester 50 V R512 63 9922 01 16 kil 5 film 1 4 W C609 22 7456 01 10 p F 20 elect 16 V R513 63 9922 01 16 kil 5 film 1 4 W C611 2...

Page 28: ... control TX202B 95 3438 1 2 Deflection yoke RX711 63 7968 59 9 1 fl 5 carbon 1 2 W TX203 95 3388 02 Power transformer RX712 63 10449 52 15 fl 5 wirebound 7 W T501 95 3136 03 Transformer horizontal driver R801 63 9921 92 6 8 fl 5 film 1 4 W TX502 95 3434 Sweep XFMR black and white final R802 63 9921 64 470 fl 5 film 1 4 W R803 63 9921 68 680 fl 5 film 1 4 W R804 63 9921 42 56 fl 5 film 1 4 W R806 6...

Page 29: ...cal amp 2 FX701 136 120 07 Fuse normal lag 2 25 amp 0604 121 819 Vertical output 1 32 V 0606 121 1036 Vertical output 2 FX201 136 114 23 Fuse 4 0 amp 0607 121 819 Vertical blanker FX202 136 113 23 Fuse 4 0 amp 0701 121 699 Error amp 1 VX201 100 718 02 CRT 12VCBP31 0702 121 975 Error amp 2 SX201 85 1610 Switch OX703 121 992 01 Regulator S202 85 1606 Switch 0801 121 895 Sync amp SX203 85 1545 03 Swi...

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Page 32: ...LLECTO BASE i COLLECTOR q T EMITTER BASE SKETCH J COLLECTOR EMI TTER SKETCH L EMI TTER COLLECT BASE EM I TER SKETCH SKETCH M 0 NUMBER 0501 0502 0601 0602 0603 0604 0606 0607 0701 Q702 OX703 0801 OB02 0803 0804 08n5 0806 BOTTOM VIEWS OF TRANS I STORS ZOS SKETCHES PART NO A B C 0 E F G H 121 B19 X 121 1028 0I 121 699 X 121 699 X 121 975 X 121 819 X 121 1036 X X 121 819 X 121 699 X 121 975 X 121 992 ...

Page 33: ...Page 9 1 CIRCUIT BOARD X RAY VIEW ...

Page 34: ...IIIENTORTESTPOINT E 15 INDICATES VEFORll I TUIIWPOIEROFFBEFOREREPLA I GSEIlICONOUCTORS E 11 CRI TICAL CI RCUI T COMPONENT 0501 HORIZ ICIilIi 001 50 call07 DRIVER _ I L o _ _ I 5O 1 01 CII06 Too 00 Rlill r I I I TO 1 1 1 1 U l l eo TClitl 0047 H I II II 1 2 11 1100 1 I I II dj IMPQRTANT SAfETY NOliCE HEN SERVICING THIS CHASSIS UNDER NO CIRCUIISTANCES SHOULD THE ORIGINAl DESIGNBEMOOIFIEDOR uTEREOIIT...