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Zenith HF 22 Service Manual

High fidelity and stereo fm
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IG
FIDELITY
AND STEREO FM MODELS
ZENIT RADIO CORPORATION
1900 N. AUSTIN AVENOE
C ICAGO. ILLINOIS G0639
F 22
PART NO. 923-642
PRICE $2.50

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  • Page 1 FIDELITY AND STEREO FM MODELS ZENIT RADIO CORPORATION 1900 N. AUSTIN AVENOE C ICAGO. ILLINOIS G0639 F 22 PART NO. 923-642 PRICE $2.50...
  • Page 2 ’ i...
  • Page 3 SPEAKER 52, 53, 54, 55, 56, 57, 58 WIRING HF 9is Zenith No. 923-606 HF 8 is Zenith No. 923-558 HF 7 is Zenith No. 923-52 HF20 is Zenith No. 923-6 0 HF 8- is Zenith No. 923-576 HF 7- is Zenith No. 923-529 HF2 is Zenith No.
  • Page 4 rtAiUKt^ Uh FIDELITY & STEREO FM MODELS CABINET C ASSIS SPEAKERS MODEL voice coil STYLE COLOR MODEI PART TYPE POWER SIZE IMPED. NUMBER (In Inches) OUTPUT I (In Ohmc) I I I*** VXilllld/ I Portable B505B I Blue & Phono Only 849-48B —...
  • Page 5 FEATURES OF FIDELITY & STEREO FM MODELS RECORD C ANGER OT ER FEATURES POWER PART RECORD STYLUS 45 RPM TAPE RECORD MOUNTING CARTRIDGE INDICATOR NUMBER SPEAKER NOTE 1 ADAPTER PROVISION STORAGE LIG T PROVISION Manual Integral 942-8B 827- 8B — —...
  • Page 6 FEATURES OF FIDELITY & STEREU MVI MUUELb SPEAKERS C ASSIS CABINET 70 ICE COIL PART SIZE IMPED. TYPE POWER COLOR MODEL MODEL STYLE (In Inches) NUMBER (In Ohms) OUTPUT 964-25775 2-6x9 Phono Only 2x4W Portable Walnut B553W (With Handle, Detachable Speaker Enclosures) 2-6x9...
  • Page 7 FtAIUKE.3 Ur niun TIUUUII I « m mvw».fcw oiurlu i OT ER FEATURES RECORD C ANGER REMOTE POWER RECORD < TAPE SPEAKER STYLUS INDICATOR STORAGE CARTRIDGE PROVISION mounting ROVISION ADAPTER LIG T NOTE 1 S-72648 42- 75 Hinged 69-408 56-560 Shelf Note 6 Note 7...
  • Page 8 ■ — ■ ■ • '">»v wi ■■■««■■ ■ iwfafal I ■ <K OILnLU rm muuLLd CABINET C ASSIS SPEAKERS VOICE COII PART SIZE MODEL STYLE COLOR MODEL TYPE IMPED. POWER NUMBER (In Inches) (in Ohms) OUTPUT C92 DE Console Dark Oak 2 BT34Z FM/AM/Phono •...
  • Page 9 rtAiuKtb ur niun nutLiiT & bitKtu rm muutLd RECORD C ANGER OT ER FEATURES REMOTE POWER TAPE RECORD STYLUS 45 RPM PART SPEAKER MOUNTING CARTRIDGE INDICATOR ADAPTER PROVISION STORAGE NOTE 1 NUMBER PROVISION LIG T Note 5 S-82965 Note 7 69-4 Shelf 42- 67...
  • Page 10 rtAiuntd ur mun & diEKtu rm muutLd nueliit SPEAKERS CABINET C ASSIS VOICE COIL PART SIZE STYLE MODEL TYPE POWER IMPED. MODEL COLOR NUMBER (In Inches) OUTPUT (In Ohms) 29AT24Z 49- 073 C966DE Console Dark Oak FM/AM/Phono 2x80W 2- 5 (Lift Lid) 6AT24 49- 094...
  • Page 11 FEATURES OF DtLIlY & bitKtu rm muutLd RECORD C ANGER OT ER FEATURES POWER REMOTE STYLUS 45 RPM TAPE RECORD PART CARTRIDGE INDICATOR SPEAKER MOUNTING NOTE 1 ADAPTER PROVISION STORAGE NUMBER PROVISION LIG T Note 4 42- 67 S-82965 Note 8 Shelf 69-4 7 S-8262...
  • Page 12 Unipolar devices. The reason being that Unipolar devices Service Manual HF- 8 (Zenith Part No. 923-558) contains a (FET ’ s) rely on majority carriers for operation, since the brief theory review of diodes (including zeners and SCR ’ s) and current flow is only thru the one material used in the channel.
  • Page 13 The electrode voltages established are; source: — 9.0 volts; drain: 0 volts; with the gate voltage at — 9.5 volts. Under this condition the FET is biased for optimum circuit performance and also low noise. As signal level increases, reverse AGC voltage will increase.
  • Page 14 Figure 2-8 MOSFET devices have added features when compared to the JFET ’ s. These include; the gates have lower leakage because they are less sensitive to temperature, higher frequency operation, and higher input resistance. Since the Gate is insulated the input resistance/ impedance will not change due to the applied bias voltage.
  • Page 15 Figure 2-11...
  • Page 16 29AT24 and 6AT24 as shown in Service Manual HF 8, voltage divider across the B+ line and provide a fixed bias to Zenith Part Number 923-558). At this time we will discuss Gate (Gl). The FM RF signal from LI is also applied to Gl.
  • Page 17 67 K zTRAP As the gain of the IF stages increases, reverse AGC voltage will be developed at diodes CR205 and CR206, and applied to the This composite information is fed to the input of the 67 KHz gate terminal (G2) of the FET. This increasing AGC voltage, trap L30 (Figure 3-3).
  • Page 18 COMPOSITE AMPLIFIER pulses perform two functions. These DC pulses are fed through resistor R3 0 and are filtered by capacitor C305 connected Now that the 67 KHz SCA material has been eliminated it is to ground. A DC voltage will be developed which will be necessary to amplify the remaining three elements of the fed back to the base of the 9KHz amplifier.
  • Page 19 Figure 3-5 BI-PLEX DETECTOR T E BIPLEX DETECTOR The 7 and volts are obtained from the voltage divider con ­ sisting of the 2.2K & 820 resistors.Note that the collector The “ N ” channel JFET used in the Biplex detector circuit and emitter are connected to the opposite ends of the 38KHz of the 29CT30 exhibits bilateral characteristics.
  • Page 20 Figure 3-7 BI-PLEX DETECTOR WIT T EORETICAL 38K z SIDE BAND WAVEFORMS An important point here is that because the FET has bilateral signal can appear at the L and R output terminals only by characteristics, the source is as shown in the schematic for the the way of the T30 transformer secondary, because any first half-cycle but the source and drain change places when the...
  • Page 21 38KHz CW (the subcarrier) into the (L - R) 38KHz side bands QUASI COMPLEMENTARY SYMMETRY and at the same time demodulates this signal into the (L - R) audio signal and also provides the matrixing of the two sets of Chassis 29CT30 uses quasi complementary symmetry output circuits which are similar to the complementary symmetry audio signal (L + R) and (L - R) according to the formulae:...
  • Page 22 Figure 3-10 QUASI COMPLEMENTARY SYMMETRY OUTPUT CIRCUIT (R476) is part of the voltage divider network (R475, R477) Q454 will offset the increased current flow in the other between collector and emitter of Q454. Setting of R476 transistors and will stabilize bias voltages. determines the bias on Q454, which in turn sets the bias and idling current of the output transistors.
  • Page 23 8 (Zenith Part No. stereo FM reception. To help determine if there is sufficient signal available, the following developed AGC voltage versus 923-558), and HF 9 (Zenith Part No. 923-606). microvolt input voltage charts have been compiled. Since the MULTIPLEX ALIGNMENT desired FM Station may not always be operating in the stereo mode when an installation is made, these AGC voltage measure ­...
  • Page 24 CIRCUIT BOARD COMPONENT IDENTIFICATION may be noted when tuning between Frequency Modulation As a special feature to aid the Service Technician, Zenith has stations. This is normal, and will disappear as the station is identified the location of components which are mounted on tuned in.

  • Page 25: Resistance Measurements

    Connect to Ratio Detector Test ’ Point “ H ” . An open or damaged section of circuit board wiring foil can be repaired by soldering a short jumper wire across the points to Connect to the last FM IF Test Point “ G ” be connected.
  • Page 26 a +- J3> > < I — < o ’ v — < < — □ < < Z ’ 00 < r- , T — r —...
  • Page 27 > ■M >* (D 2_ 03 "5 CD "cu I??* &.<2 £ t ° E o = 4-» __ : -• ” E C ■ — ■ ’ c -M CD *Z < Ei=PaZ > _ CM — J CM CO CM CM -J CM —...
  • Page 28 < < < □ < < < r “ 4...
  • Page 29 To help achieve this IF curve symmetry 0.6 and portion of Zenith or any FM multiplex receiver can be aligned, megahertz markers must be symmetrically positioned and the but first before any attempt is made to do this it is necessary 0.7 megahertz marker must be at the center of the curve.

  • Page 30: Trouble-S Ooting

    The composite signal is very useful since it is an excellent tool 6. Turn generator pilot carrier amplitude control to 5% that can be used in signal tracing the multiplex portion of the position. receiver. We do not recommend that multiplex alignment be 7.
  • Page 31 3. Move the L+R switch from OFF up to L+R and look at the Doubler and Subcarrier Signal Tracing L audio output, and measure the magnitude of the hertz sine wave. If the multiplex detector and proceeding To determine if the doubler is functioning, place your scope at circuitry are aligned properly, the magnitude of the wave the junction of the two diodes and you will see 38KHz DC form at L should be greater than at R.

  • Page 32: Parts List

    000 MF Electrolytic Capacitor - 50V. 36-6 Fuse - 3 Amp. (Type C) (2 Required) 4.05 2 2-62 Silicon Rectifier (2 Required) 3. 0 22-5455 50 MF Electrolytic Capacitor - 50V. * Denotes parts not previously used in Zenith receivers.
  • Page 33 CONTROL PANEL PRE-AMP. COMPONENTS 86-390 Connector Terminal (8 Used On 43-57 ) Connector Terminal (Used On 52- 39 ) 86-599 2-4903 Control Panel Bracket *94- 384 Insulating Bushing 9-480 Clip (2 Required) •Denotes parts not previously used in Zenith receivers.
  • Page 34 2 Conductor Shielded Lead (Used On 86-599) 22-3675 0 PF Disc Capacitor ± 5% - 500V. 63- 8 3 4700 Ohm Resistor - V2W. 0% (2 Required) 22-3687 MF Electrolytic Capacitor - 50V. (2 Required) ‘ Denotes parts not previously used in Zenith receivers.
  • Page 35 Nylon Insulating Bushing (Use Only When 800-3 2 63- 768 390 Ohm Resistor - V^W. 0% Is Used) (4 Required) 63- 769 430 Ohm Resistor - ^W. 5% (4 Required) 95-254 Transformer - AM st. I.F. 455 KHz ♦Denotes parts not previously used in Zenith receivers...
  • Page 36 PC Board Support Frame S-86475) (2 Required) *33-327 * 2-5524 43-57 9 Contact Housing (Used On 86-390) Control Mtg. Bracket 7- 30 Cable Clamp 44-48 Connector Jack (4 Part Of S-79667) ‘ Denotes parts not previously used in Zenith receivers.
  • Page 37 63-7682 2.50 Dual Bass Control - 00K Ohm 2 -737 Transistor - Stereo Indicator Switch 2.95 63-7683 Dual Loudness Control 2 -762 Transistor - Detector 3.30 63-7684 Balance Control & Switch ’ Denotes parts not previously used in Zenith receivers.
  • Page 38 63- 845 27K Ohm Resistor - ’ A W. 0% (2 Required) -OR- 63- 848 33K Ohm Resistor - ’ A W. 0% (4 Required) 270 PF Mica Capacitor - 00V. 22-3424 •Denotes parts not previously used in Zenith receivers.
  • Page 39 6-20 x 5/ 6 Hex Washer Hd. Self-Tap. Screw-Stat. 4-77 22-3080 .005 MF Ceramic Disc Capacitor 25 V. Bronze ( Mts. 83-7 96 & 2 Mt. 2-5358) (2 Required) & 57-7637) (5 Required) •Denotes parts not previously used in Zenith receivers...
  • Page 40 Dual BassjControl - 00K Ohm W. 30% 58-338 Plug Shorting Bar *63-8998 Dual Treble Control - 50K Ohm /8W. 30% *59- 0 Pointer (Down Blade With Carriage) *63-8999 Dual Loudness Control - 00K Ohm /8W. 30% ♦Denotes parts not previously used in Zenith receivers.
  • Page 41 20 MMF Ceramic Disc Capacitor -500V. Transistor (Stereo Indicator) 2 -737 22-3770 5.5 PF Disc Capacitor - 500V. 2 -767 Bias Transistor (2 Used On P.C. Board) 22-3896 5 MF Electrolytic Capacitor - 25V. ♦Denotes parts not previously used in Zenith receivers.
  • Page 42 63- 782 820 Ohm Resistor - V2W. 0% *83-8 48 Insulating Strip (Flat Stop With Perforation) 63- 785 000 Ohm Resistor - y 2 W. 0% (2 Required) *83-8 67 Insulating Strip ‘ Denotes parts not previously used in Zenith receivers.
  • Page 43 9 Contact Housing - Male 43-57 S-89 8 Pulley & Bracket Assem. (Front) 43-875 9 Contact Housing - Male S-89 22 FM Detector Coil Assem. 43-878 2 Contact Housing - Female (2 Required) •Denotes parts not previously used in Zenith receivers.
  • Page 44 6.35 63- 859 56K Ohm Resistor - AW. 0% (2 Required) *85- 077 4.45 AFC Switch 63- 862 68K Ohm Resistor - AW. 0% (2 Required) *85- 078 Function Switch (6 Required) *Denotes parts not previously used in Zenith receivers.
  • Page 45 Transistor - F.M.B. - Switching. A.M.B. - ‘ / 63-4283 220K Ohm Resistor - ’ /.W. 0% Switching, Stereo B - Switch, Ext. Bass Switch (4 Required) 63-4297 470K Ohm Resistor - W. 0% ♦Denotes parts not previously used in Zenith receivers.
  • Page 46 Thread - Forming Palnut (2 Mt. Ea. 57-755 & 20- 422 Peaking Coil 57-7552) (4 Required) 20-2008 Peaking Coil 54-579 0-32 x 3/8 Hex Nut - Steel - Cadmium (Mts. 20-2033 Peaking, Coil (2 Required) 03- 58) * Denotes parts not previously used in Zenith receivers...
  • Page 47 47 Megohm Resistor - VM, 0% 2.30 *95-272 st, I.F. Transformer (AM) *63-8244 Dual Loudness Control *95-2722 2nd. I.F. Transformer (AM) 2.65 Potentiometer *63-8258 3rd. I.F. Transformer (AM) 3.50 *95-2723 *63-8259 Bass Slide Control ‘ Denotes parts not previously used in Zenith receivers.
  • Page 48 Iron Core Bushing (4 Required) Silicon Controlled Rectifier (FM Switch, AM * 85-3 94- 472 Tuning Shaft Bushing Switch, Phono Switch, Tape Switch) 95-2322 st, I.F. Transformer (FM) 2. 5 (4 Required) 3.50 03-47 Diode 3.75 •Denotes parts not previously used in Zenith receivers.
  • Page 49 47 MF Disc Capacitor - 3V. (2 Required) 63- 84 22K Ohm Resistor - y 2 W. 0% 270 PF Polystyrene Capacitor - 500V. *22-5780 63- 842 22K Ohm Resistor - y 2 W. 20% •Denotes parts not previously used in Zenith receivers.
  • Page 50 500 Ohm Resistor - V2W. 0% (2 Required) *95-2754 Transformer - FM 2nd. I.F. 0.7 MHz *964- 582 6800 Ohm Resistor -W. 0% *95-2755 Transformer - FM 3rd. I.F. 0.7 MHz *964- 359 8200 Ohm Resistor - V2W. 0% •Denotes parts not previously used in Zenith receivers.

  • Page 51: Cabinet Components

    *964- 6579 964-23 38 Strike - Chrome (2 Required) Eyelet, Pivot Assem. (2 Required) 964- 6580 *964-23279- A Logo - Zenith 4.7 Ohm Resistor - I4W. 0% (2 Required) 964- 6699 *964-23362 Amp. Terminal Tee Nut, Pivot Assem. (2 Required)
  • Page 52 Antenna Jack S-834 Antenna Coil Assem. 56-426 Roll Pin (6 Used On 76- 820) S-834 2 R.F. Input Coil Assem. 57-5333 Bearing Plate 63- 778 680 Ohm Resistor - YzW. 0% ‘ Denotes parts not previously used in Zenith receivers.
  • Page 53 MEC ANICAL ASSEMBLIES Zenith engineers have devised chassis constructions which, while maintaining a compact package size, will provide maximum access to the chassis should service be required. Illustrated here is one chassis configura ­ tions with instructions for tilting sub chassis into working position.
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  • Page 66 6ZT20 C ASSIS LAYOUT...
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  • Page 70 < I < <...
  • Page 71 16CT21 - C ASSIS LAYOUT...
  • Page 72 LEGEND C ASSIS 16CT21 ITEM PART DESCRIPTION NUMBER C401 22-3034 .05 MFD DISC 25 V C402 22-6343 .33 MFD 20% 50 V C404 22-3687 1 MFD ELECTROLYTIC 50 V C405 22-3255 330 PF DISC 500 V C406 22-5483 1500 PF 500 V C407 22-5884 .082 MFD 100 V...
  • Page 73 16CT21 - POWER AMP - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE 16CT21 - PRE AMP - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE...
  • Page 74 21BT34 AND 21BT34Z1 - SC EMATIC...
  • Page 75 LEGEND C ASSIS 21BT34 AND 21BT34Z1 ITEM PART ITEM PART DESCRIPTION DESCRIPTION NUMBER NUMBER F.M. DETECTOR ” TRIMMER R212 63-1772 470 O M 20% F.M. DETECTOR TUNING R213 63-1778 680 O M R214 63-1778 680 O M F.M. OSCILLATOR TUNING A.M.
  • Page 76 21BT34 AND 21BT34Z1 - C ASSIS LAYOUT...
  • Page 77 27BT30 - C ASSIS LAYOUT...
  • Page 78 27BT30 - SC EMATIC...
  • Page 79 LEGEND C ASSIS 27BT30 ITEM PART ITEM PART ITEM PART DESCRIPTION DESCRIPTION DESCRIPTION FM DETECTOR TRIMMER C463 226110 .033 MFD 20% 50V R425 63-1776 620 O M 5% F.M. DETECTOR TUNING C464 22-5988 1 MFD ELECTROLYTIC 15V R426 63-8328 300 O M BIAS ADJUST F.M.
  • Page 80 LEGEND C ASSIS 29CT20 ITEM PART ITEM PART DESCRIPTION DESCRIPTION NUMBER NUMBER 39KO M FM ANT TRIMMER R226 63-1852 47K O M FM ANT TUNING R227 63-1855 R228 63-1852 39K O M FM DETECTOR TRIMMER 120K O M FM DETECTOR TUNING R229 63-1873 56K O M...
  • Page 81 2pCT20 - POWER AMP - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE 29CT20 - PREAMP - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE...
  • Page 82 29CT20 AND 29CT21 - RF/IF - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE...
  • Page 83 29CT20 AND 29CT21 - C ASSIS LAYOUT...
  • Page 84 LEGEND C ASSIS 29CT21 ITEM PART ITEM PART DESCRIPTION DESCRIPTION NUMBER NUMBER FM ANT TRIMMER R229 63-1873 120KO M FM ANT TUNING R230 63-1859 56K O M FM DETECTOR TRIMMER R231 63-1820 6.8K O M FM DETECTOR TUNING [R232 63-1778 680 O M FM OSC.
  • Page 85 29CT21 - POWER AMP - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE 29CT21 — PREAMP — C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE...
  • Page 86 29AT24 - SC EMATIC...
  • Page 87 LEGEND C ASSIS 29AT24 AND 29AT2' 121 ITEM PART DESCRIPTION ITEM PART DESCRIPTION P * ” T DESCRIPTION DESCRIPTION AM ANTENNA TUNING 22-5012 R235 63-1813 4.7K O M 634883 L304 INT303 DOUBLER COIL 19K z (PRI.) AM ANTENNA TRIMMER 63-1869 100K O M 22MEGO M L3O5...
  • Page 88 29AT24Z1 - SC EMATIC...
  • Page 89 29AT24 AND 29AT24Z1 - C ASSIS WIRING AND COMPONENTS VIEWED FROM FOIL SIDE...
  • Page 90 29CT30 - SC EMATIC...
  • Page 91 LEGEND C ASSIS 29CT30 ITEM PART ITEM PART DESCRIPTION DESCRIPTION NUMBER NUMBER R219 63-1841 22K O M FM ANT TRIMMER R220 63-1785 1KO M FM ANT TUNING R221 63-1834 15K O M FM DETECTOR TRIMMER 1KO M R222 63-1785 FM DETECTOR TUNING R223 63-1904 680K O M...
  • Page 92 29CT30 - C ASSIS LAYOUT...
  • Page 94 ZENIT RADIO CORPORATION 1900 N. AUSTIN AVENUE C ICAGO, ILLINOIS 60639 SPECIFICATIONS SUBJECT TO C ANGE WIT OUT NOTICE PRINTED IN U.S.A. 3-642 F 22 RR 6/7...

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