CI M800 SL2 Part C T854 Transmitter This part of the manual is divided into six sections, as listed below. There is a detailed table of contents at the start of each section.
CII 01/03/02 M800 SL2 Copyright TEL
T854 General Information M800 SL2 1 C1.1 T854 General Information This section provides a brief description of the T854 transmitter, along with detailed specifications and a list of types available. The following topics are covered in this section. Section Title Page 1.1 Introduction 1.7 1.2 Specifications 1.8 1.2.1 Introduction 1.8 1.2.2 General 1.8 1.2.3 RF Section 1.9 1.2.4 1.2.4.1 1.2.4.2 1.2.4.3 Audio Processor Inputs Modulation Characteristics CTCSS 1.10 1.10 1.11 1.11 1.2.
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M800 SL2 T854 General Information C1.3 Figure 1.1 T854 Main Circuit Block Identification replace this page with A3 8500C1xx.
C1.4 T854 General Information M800 SL2 Figure 1.2 T854 Front Panel Controls replace this page with A3 8500C1xx.
T854 General Information M800 SL2 1.1 C1.5 Introduction The T854 is a synthesised, microprocessor controlled FM base station transmitter designed for single or multichannel operation in the 400 to 520MHz frequency range1 with a standard power output of 25W. The RF section of the transmitter comprises a frequency synthesiser which provides 100mW of frequency modulated RF drive to a two stage, wide band output driver followed by a 25W power supply.
C1.6 T854 General Information 1.2 Specifications 1.2.1 Introduction M800 SL2 The performance figures given are minimum figures, unless otherwise indicated, for equipment tuned with the maximum switching range and operating at standard room temperature (+22°C to +28°C) and standard test voltage (13.8V DC). Where applicable, the test methods used to obtain the following performance figures are those described in the EIA and ETS specifications.
T854 General Information M800 SL2 C1.7 Overall Dimensions: Height Width Depth .. 132mm .. 480mm .. 335mm Weight with Tone Remote Weight without Tone Remote .. 16kg .. 13kg Time-Out Timer (optional) .. 0 to 5 minutes1 adjustable in 10 second steps Tail Timer .. 0 to 5 seconds adjustable in 100ms2 steps Transmit Key Time .. <30ms Transmit Lockout Timer .. 0 to 1 minute adjustable in 10 second steps 1.2.3 RF Section Frequency Range .. 400-520MHz (refer to Section 1.4 and Section 1.
C1.8 T854 General Information M800 SL2 Transmitter Side Band Noise: (no modulation, 15kHz bandwidth) At ±25kHz At ±1MHz Intermodulation .. -95dBc .. -105dBc .. -40dBc with interfering signal of -30dBc .. -70dBc with 25dB isolation & interfering signal of -30dBc (PA with output isolator) T854 Mismatch Capability: Ruggedness Stability .. refer to your nearest Tait Dealer or Customer Service Organisation .. 3:1 VSWR (all phase angles) Radiated Spurious Emissions: Transmit Standby ..
T854 General Information M800 SL2 Sensitivity (60% modulation @ 1kHz)With Compressor Without Compressor 1.2.4.2 C1.9 .. -70dBm .. -50dBm Modulation Characteristics Frequency Response (below limiting) .. flat or pre-emphasised (optional) Line And Microphone Inputs: Pre-emphasised ResponseBandwidth Below Limiting Flat Response .. 300Hz to 3kHz (WB & MB) .. 300Hz to 2.55kHz (NB) .. within +1, -3dB of a 6dB/octave pre-emphasis characteristic ..
C1.10 T854 General Information 1.2.5 Microcontroller M800 SL2 Auxiliary Ports: Open Drain Type Vds max. 1.2.6 .. capable of sinking 2.25mA via 2k2Ω .. 5V Test Standards Where applicable, this equipment is tested in accordance with the following standards. 1.2.6.
T854 General Information M800 SL2 1.3 C1.11 Product Codes The three groups of digits in the T850 Series II product code provide information about the model, type and options fitted, according to the conventions described below. Consult your nearest Tait Dealer or Customer Service Organisation for more information regarding the availability of specific models, types and options.
C1.12 T854 General Information 1.4 T854 Standard Product Range M800 SL2 The following table lists the range of standard T854 types (i.e. no options fitted) available at the time this manual was published. Consult your nearest Tait Dealer or Customer Service Organisation for more information. Frequency Range (MHz) Deviation (kHz) TCXO ±1ppm -20°C to +60°C Transmitter Type: T854- 400-440 2.5 2.
T854 General Information M800 SL2 T800 SL BSM Conventional Ordering Number System System Type Frequency Band RF Output Power Channel Spacing Coaxial Relay / Duplexer Power Supply 3/13/02 Ancillary Options L A 1 W B 0 0 1 2 3 4 1 L = T800 SL BSM (T800-56-X0XX) 7 A = 66 - 88 MHz (T82x-xx-02xx) B = 136 - 156 MHz (T83x-1x-02xx) C = 148 - 174 MHz (T83x-2x-02xx) D = 400 - 440 MHz (T85x-1x-02xx) E = 440 - 480 MHz (T85x-2x-02xx) F = 480 - 560 MHz (T85x-3x-02xx) P = 800 - 870 MHz (T88x-1x-02xx) * Q
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M800 SL2 Copyright TEL T854 General Information C1.
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T854 Circuit Operation M800 SL2 2 C2.1 T854 Circuit Operation This section provides a basic description of the circuit operation of the T854 transmitter. Unless otherwise specified, the term "PGM800Win" used in this and following sections refers to version 3.00 and later of the software. Note: Refer to Section 6 where the parts lists, grid reference index and diagrams will provide detailed information on identifying and locating components and test points on the main PCB.
C2.2 T854 Circuit Operation Figure M800 SL2 Title Page 2.1 T854 High Level Block Diagram 2.3 2.3 T854 Microcontroller Block Diagram 2.4 2.4 T854 Synthesiser Block Diagram 2.5 2.5 T854 Two Point Modulation 2.6 2.6 T854 Audio Processor Block Diagram 2.8 2.7 T854 Power Supply & Regulators Block Diagram 2.10 2.8 T854 Transmit Timers 2.
T854 Circuit Operation M800 SL2 2.1 C2.3 Introduction The individual circuit blocks which make up the T854 are: • synthesiser • VCO • audio processor • drive amplifier • voltage regulators. Each of these circuit blocks is set in its own shielded compartment, formed as an integral part of the main chassis. The configuration of the circuit blocks may be seen on a functional level in Figure 2.1 . Refer to the circuit diagrams in Section 6.2 for more detail. PIN Switch Reference Oscillator 12.
C2.4 T854 Circuit Operation 2.2 Microcontroller M800 SL2 (Refer to the microcontroller circuit diagram (sheet 8) in Section 6.2 or 6.3.) Watchdog Reset 5V Digital Regulator 5V Reset Microcontroller Cavity Channel Select Port 12.8MHz Clock External Serial Port CTCSS Tone Microcontroller Auxiliary Output Port Dual Digital Potentiometer Converter CTCSS Encoder EEPROM Synthesiser Figure 2.
T854 Circuit Operation M800 SL2 2.3 C2.5 Synthesised Local Oscillator (Refer to the synthesiser circuit diagram (sheet 7) in Section 6.2 or 6.3 and the VCO circuit diagram in Part E.) VCO Modulation FREQUENCY SYNTHESISER IC 12.8MHz Reference Oscillator Fixed Divider Reference Divider /64 Phase Detector Charge Pump Loop Filter VCO Serial Bus Phase Modulator Clk Data En Buffer Σ /R fref Ref Mod VCO PCB Programmable Divider Prescaler /N 64/65 Output Buffer +22dBm L.O.
C2.6 T854 Circuit Operation 2.3.1 Two Point Modulation M800 SL2 Frequency modulation occurs by modulating both the VCO input and the synthesiser reference input. This process is called two point modulation and ensures a flat modulation response from 67Hz to 3kHz (2.55kHz for narrow bandwidth). The PLL has a fast response time, allowing a Tx key-up time of <30ms.
T854 Circuit Operation M800 SL2 2.4 C2.7 VCO (Refer to the VCO circuit diagram in Part E.) The VCO transistor (Q1) operates in a common emitter configuration, with an LC tank circuit coupled between its gate and drain to provide the feedback necessary for oscillation. The VCO control voltage from the loop filter (IC750) is applied to the varicaps (D1-D2) to facilitate tuning within an 8MHz band of frequencies. A trimcap (C6) is used for coarse tuning of the VCO.
C2.8 T854 Circuit Operation 2.5 Audio Processor M800 SL2 (Refer to the audio processor circuit diagram (sheet 2) in Section 6.2 or 6.3.) Carrier Opto-coupler + Opto-Key Tx Enable _ Constant Current Sink Tx Key 4 6 8 PTT 3 5 Link 4 B 6 C PL205 mic. Line Input Compressor Output Inhibit Inputs Microphone Input Output Microphone Pre-amp. line Limiter Set Deviation 6 4 2 Link 5 N 3 M 1 L PL210 Digital Pot.
T854 Circuit Operation M800 SL2 2.5.3 C2.9 Keying Inputs There are four ways to key the exciter: • pulling the Tx-Key line low (pin 13 on D-range 1 [PL100]) at the rear of the set); • pushing the "Carrier" button on the front panel - this will inhibit all audio; • using the PTT button on the local microphone, disabling audio from the line; • via the opto-key inputs (pins 11 and 12 on D-range 1 [PL100]) when electrical isolation is required.
C2.10 T854 Circuit Operation 2.6 Power Supply & Regulator Circuits M800 SL2 (Refer to the regulators circuit diagram (sheet 6) in Section 6.2 or 6.3.) Figure 2.6 T854 Power Supply & Regulators Block Diagram +9V Buffer Power Switch Microcontroller Tx Enable IC 370 Tx Reg. 9v Ex 9v Reg Watchdog Timer 13.8V Nom. From Rear D-Range DC Amp 5V Reg Crowbar Diode 13.8V Nom. 5V 5V Dig Reg Switching PS 9V 20V LVI µP µP Reset 5V Dig The T854 are designed to operate from a 10.
T854 Circuit Operation M800 SL2 2.7 C2.11 Transmit Timers The transmit tail timer, transmit timeout timer and transmit lockout timer can all be set from PGM800Win. The fields for setting these are found on the system information page. These three timers operate as follows (refer also to Figure 2.7): Timer Function Adjustment Transmit Tail Sets the tail time during which the transmitter stays keyed after the external key source has been removed.
C2.12 T854 Circuit Operation 2.8 T854 Drive Amplifier & PA M800 SL2 (Refer to Figure 2.1 and the exciter and PA circuit diagrams (sheets 3 & 4) in Section 6.2.) The output power of the PA is maintained at a constant level via a power control loop applied to the two-stage, wide band exciter amplifier (Q337, Q336). The forward and reverse RF power levels are sensed via a dual directional coupler and detector diodes (D440, D420 in the PA cavity).
M800 SL2 Copyright TEL T854 Circuit Operation C2.
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T854 Initial Tuning & Adjustment M800 SL2 3 C3.1 T854 Initial Tuning & Adjustment Caution: This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices.
C3.2 T854 Initial Tuning & Adjustment Section 3.5 M800 SL2 Title Page Audio Processor Links 3.8 3.5.1 Link Details 3.8 3.5.2 Typical Options 3.8 3.6 Synthesiser Alignment 3.9 3.7 PA Alignment 3.10 3.8 Thermal Shutdown 3.10 3.9 Audio Processor & CTCSS 3.11 3.9.1 Two Point Modulation 3.11 3.9.2 Modulator Adjustment 3.11 3.9.3 CTCSS Encoder (If Used) 3.12 3.9.4 Limiter Adjustment 3.12 3.9.5 Line Level Without Compressor 3.13 3.9.6 3.9.6.1 3.9.6.2 3.9.6.
T854 Initial Tuning & Adjustment M800 SL2 3.1 C3.3 Introduction When you receive your T854 transmitter it will be run up and working on a particular frequency (the "default channel")1. If you want to switch to a frequency that is within the 8MHz switching range (i.e. ±4MHz from the factory programmed frequency), you should only need to reprogram the transmitter/exciter with the PGM800Win software (refer to the PGM800Win programming kit and Section 3.2 below).
C3.4 T854 Initial Tuning & Adjustment 3.3 Test Equipment Required M800 SL2 You will need the following test equipment: • computer with PGM800Win installed • T800 programming kit • module programming interface (e.g. T800-01-0004 - optional) • 13.8V power supply • digital multimeter • audio signal generator • RF power meter • audio voltmeter x 2 or RF test set (optional) • modulation meter • oscilloscope (digital preferred) • 20dB or 40dB pad • T800-01-0010 calibration test unit (optional) Figure 3.
T854 Initial Tuning & Adjustment M800 SL2 3.4 C3.5 Short Tuning Procedure Use this procedure only if you want to reprogram the T854 to a frequency outside the 8MHz switching range and do not intend to carry out any other major adjustments or repairs. 3.4.1 Introduction Reprogram the operating frequency as described in the PGM800Win programming kit (refer to Section 3.2). Remove the top cover (nearest the handle). Set up the test equipment as described in Section 3.3.
C3.6 T854 Initial Tuning & Adjustment 3.4.4 Two Point Modulation Adjustment Note 1: In this and following sections deviation settings are given first for wide bandwidth sets, followed by settings in brackets for mid bandwidth sets ( ) and narrow bandwidth sets [ ]. Note 2: The reference modulation and limiter adjustments are controlled by 256step electronic potentiometers (EPOTs), which are adjusted via the “Reference Modulation” and “Deviation” settings in PGM800Win.
T854 Initial Tuning & Adjustment M800 SL2 3.4.5 C3.7 CTCSS Encoder (If Used) Program a CTCSS tone on the default channel using PGM800Win. If you are using an RF test set, turn off the 300Hz high pass filter. Key the T854 with the front panel "Carrier" switch. Adjust RV805 (CTCSS level adjust) to give ±500Hz (±350Hz) [±250Hz] deviation. Set the maximum deviation as per Section 3.4.6. 3.4.
C3.8 T854 Initial Tuning & Adjustment 3.5 Audio Processor Links 3.5.1 Link Details M800 SL2 Use the following table to set up the audio processor to the configuration you require. You should set the audio processor links before carrying out any of the tuning and adjustment procedures. The factory settings are shown in brackets [ ]. Linka Plug PL205 PL210 PL215 PL220 Function 1-2 A not connected [3-4] B microphone pre-amp. output to compressor input 5-6 C microphone pre-amp.
T854 Initial Tuning & Adjustment M800 SL2 3.6 C3.9 Synthesiser Alignment • Ensure that the T854 has been programmed with the required frequencies using PGM800Win software. • Single Channel Select a channel using PGM800Win. Multichannel Select the middle channel via PGM800Win. • Connect a high impedance voltmeter to the long lead of L1 in the VCO (this measures the synthesiser loop voltage). • Key the transmitter by earthing the Tx-Key line.
C3.10 T854 Initial Tuning & Adjustment 3.7 PA Alignment M800 SL2 Check that the exciter is connected to the PA with the coaxial link. Connect an RF power meter to the PA output (use an appropriate attenuator as necessary). Turn RV310 (power control) fully clockwise. Key the transmitter by earthing the Tx-Key line. Tune #CV475 until maximum power is obtained. Check that the power exceeds 30W. Adjust RV310 (power control) to 25W. Readjust #CV475 to reduce the supply current by up to 0.5A. 3.
T854 Initial Tuning & Adjustment M800 SL2 3.9 Audio Processor & CTCSS 3.9.1 Two Point Modulation C3.11 The T854 utilise two point modulation to obtain a wide audio bandwidth independent of the synthesiser loop filter response. This is achieved by simultaneously frequency modulating the VCO and phase modulating the synthesiser reference frequency. The relative signal levels fed to the two modulators are quite critical and cause interaction when setting up.
C3.12 4. T854 Initial Tuning & Adjustment M800 SL2 Change the input frequency back to 300Hz. Repeat steps 2 and 3 above until the deviations achieved at the two input frequencies are within 0.2dB of each other. You will need to do this at least four times. 5. Sweep the audio between 50 and 300Hz for peaks. A peak between 50 and 300Hz will indicate a fault condition, i.e: Note: or - incorrect set-up - modulation circuitry fault. The specification window is ±1dB relative to 150Hz from 67 to 260Hz.
T854 Initial Tuning & Adjustment M800 SL2 3.9.5 C3.13 Line Level Without Compressor This section assumes that the compressor is not used. If the compressor is required, refer to Section 3.9.6. Remove the CTCSS signal (if used). Adjust the line sensitivity as follows: • set the injected signal at the line input to the required line level (typically -10 to -20dBm); • adjust RV210 (line sensitivity) to provide ±3kHz (±2.4kHz) [±1.5kHz] deviation. Reapply the CTCSS signal (if required). 3.9.
C3.14 T854 Initial Tuning & Adjustment M800 SL2 Increase the audio level until the demodulated waveform shows significant signs of clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation). Adjust RV220 anticlockwise until the demodulated waveform is just clipping (approximately ±4kHz (±3.2khz) [±2kHz] deviation). Increase the audio level by 10dB and verify that the test tone is held just into clipping. Whistle steadily into the microphone, checking that approximately ±4kHz (±3.
T854 Functional Testing M800 SL2 4 C4.1 T854 Functional Testing Caution: This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices. The following test procedures will confirm that the T854 has been tuned and adjusted correctly and is fully operational.
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T854 Functional Testing M800 SL2 4.1 C4.3 Current Consumption Connect the T854 to a 13.8V power supply. Connect an RF power meter to the T854 output socket. Check that the current in the 13.8V power cable is less than 150mA. Key the T854 by earthing the Tx-Key line (the carrier "On" LED should light). T854 Only: Adjust RV310 (power control) to obtain 25W output power. Check that the current is as follows: T854 4.2 <5.
C4.4 T854 Functional Testing M800 SL2 Transmit Tail Sets the tail time during which the transmitter stays keyed after the external key source has been removed. 0-5 seconds in 100ms stepsa Transmit Timeout Sets the maximum continuous transmission time. Once the timer has timed out, the transmitter must be keyed again, unless prevented by the transmit lockout timer.
T854 Functional Testing M800 SL2 C4.5 The response should closely match that shown in Figure 4.3. Wide Bandwidth Peak + max. dev. = +1.0kHz @ 1000Hz Peak - max. dev. = -1.0kHz @ 1000Hz +10 +8 +6 Modulation Level (dB ref. to dev. @ 1kHz) +4 +2 +0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 100 200 300 500 1k 2k 3k 5k 10k Frequency (Hz) Mid Bandwidth The mid bandwidth graph is the same shape as the wide bandwidth graph. The deviation figures are as follows: peak + max. deviation = +0.
C4.6 T854 Functional Testing M800 SL2 Wide Bandwidth Peak + max. dev. = +4.9kHz @ 1500Hz Peak - max. dev. = -4.4kHz @ 2500Hz Above limiting (steady-state) +10 +8 +6 Modulation Level (dB ref. to max. dev.) +4 +2 +0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 10 20 30 50 100 200 300 500 1k 2k 3k 5k 10k Frequency (Hz) Mid Bandwidth The mid bandwidth graph is the same shape as the wide bandwidth graph. The deviation figures are as follows: peak + max. deviation = +4kHz peak - max.
T854 Functional Testing M800 SL2 4.6 C4.7 Audio Level Input Sensitivity • Adjust RV210 (line sensitivity) fully clockwise. • Check that the input sensitivities are better than those specified below: Line Input Microphone Input CTCSS Input Note: Copyright TEL 600 ohms, ±3kHz (±2.4kHz) [±1.5kHz] deviation at 1kHz: with compressor -50dBm without compressor -30dBm 600 ohms, ±3kHz (±2.4kHz) [±1.
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T854 Fault Finding M800 SL2 5 C5.1 T854 Fault Finding Caution: This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices. The following test procedures and fault finding flow charts may be used to help locate a hardware problem, however they are by no means a complete fault finding procedure.
C5.2 T854 Fault Finding Section 5.7 M800 SL2 Title Page Fault Finding Charts 5.8 5.7.1 5.7.1.1 5.7.1.2 5.7.1.3 Microcontroller Basic Checks Serial Communications CTCSS Encode 5.8 5.8 5.9 5.10 5.7.2 Regulator 5.11 5.7.3 Synthesiser 5.12 5.7.4 T854 Drive Amplifier 5.15 5.7.5 T854 PA & Power Control 5.16 5.7.7 Audio Processor 5.18 To Replace The T854 PA Transistors (Q410 & Q420) 5.19 5.8 Figure Title Page 5.1 RF Diode Probe Circuit 5.5 5.
T854 Fault Finding M800 SL2 5.1 C5.3 Visual Checks Remove the top cover from the T854 and inspect the PCB for damaged or broken components, paying particular attention to the surface mounted devices (SMD's). Check for defective solder joints. If repair or replacement is considered necessary, refer to Section 3 of Part A. 5.2 Component Checks If you suspect a transistor is faulty, you can assess its performance by measuring the forward and reverse resistance of the junctions.
C5.4 T854 Fault Finding 5.4 DC Checks 5.4.1 Power Rails M800 SL2 Refer to the test points and options diagrams in Section 6 for test point locations, and to the regulator fault finding chart (Section 5.7.2) for fault diagnosis. Check the 13.8V (TP601) and 9V (TP602) supplies at their test points in the regulator compartment with a DMM. Check the 5V (TP604) and 20V (TP603) rails at their respective test points in the regulator compartment. Check that Tx-Reg.
T854 Fault Finding M800 SL2 5.5 C5.5 RF Checks In-circuit RF levels may be measured with an RF probe on which the earth lead has been shortened to a minimum (i.e. 13mm). Refer to the circuit diagrams for typical levels. Figure 5.1 shows a suitable RF probe circuit.. 1n Probe Coax 10k DC to DVM or Oscilloscope 1N6263 1n 100k Earthing Clip This unit is not suitable for use on high power RF circuits. Figure 5.1 RF Diode Probe Circuit 5.5.
C5.6 T854 Fault Finding M800 SL2 Check that the demodulated RF output has the frequency response referred to in Section 4.5 with at least ±5kHz (±4kHz) [±2.5kHz] deviation available at 1kHz modulating frequency. If the above result is not achieved, either the two modulators are incorrectly adjusted or a fault condition exists.
T854 Fault Finding M800 SL2 5.6 C5.7 PGM800Win Generated Errors The following errors are those most likely to occur using PGM800Win. Refer to the PGM800Win software user’s manual for a complete list of error messages. Channel Switch Set The programmed default channel change was not accepted by the base station because a channel is selected externally. Try turning the external channel switch off to change the default channel in PGM800Win.
C5.8 T854 Fault Finding 5.7 Fault Finding Charts Note: The standard test point designations used in this section are as follows: TP601 TP602 TP603 TP604 M800 SL2 13.8V 9V 20V 5V 5.7.1 Microcontroller (IC810) 5.7.1.1 Basic Checks Is the 12.8MHz clock present on IC810 pin 21 (microcontroller)? N Check IC710. Y Replace IC810. N Is pin 30 pulsing? Y Replace IC650. Pulsing Check the state of pin 10. High or open circuit Low Check state of pins 36 to 43.
T854 Fault Finding M800 SL2 5.7.1.2 C5.9 Serial Communication Disconnect the programming lead. Is IC810 pin 11 high? (microcontroller) Low/floating N Check pin state. Check the transistor interface circuitry. Noise on pin Y Check the SERIAL-COM and AUDIO-1/2 links. Connect the programming lead and use PGM800Win to read the rack/radio. Check I/O pad P810 with a DSO*.
C5.10 T854 Fault Finding 5.7.1.3 CTCSS Encode Use PGM800Win to select a channel with a CTCSS tone programmed. M800 SL2 Cannot select a channel Check serial communications. (See separate flow chart). Y Check IC810 pins 24, 25 & 26 (microcontroller). Are there 5V square waves at the CTCSS frequency? No square waves or uneven mark/space ratio Replace IC810. Y Check IC830 pins 1, 7 & 14.
T854 Fault Finding M800 SL2 5.7.2 C5.11 Regulator Check for overheating components & short circuits. N 13.8V present on IC630 pin 3? Check continuity from pin 9 of D-range 1. Y N 5.3V present on IC630 pin 1? Replace IC630. Y 9.0V present on TP602? N Check Q630, Q620 & IC640. Y 20V present on TP603? N Check Q660 is switching at approx. 150kHz. Y +5V present on IC610 pin 1? N Check R615. Replace IC610. Y Key Tx. 8.8V present on Tx reg. TP305? Y Regulators OK.
C5.12 T854 Fault Finding 5.7.3 Synthesiser M800 SL2 Refer to the synthesiser circuit diagram (sheet 7) in Section 6 and the VCO circuit diagram in Part E. A B No VCO RF output. VCO out of lock. N 9V present at VCO Q4/Q5? Check Tx reg., Q610 & 9V reg. +5V present at IC700, IC710, IC740, IC720 & IC730? Y Check biasing resistors, Q4 & Q5. 20V present on IC750 pin 8? Y 8.3V present at VCO? N 9V present on Q795 divider buffer? Y 20V inverter supply faulty. N Check 9V supply.
T854 Fault Finding M800 SL2 C5.13 B Continued from previous page Check microcontroller section (IC810). Replace synthesiser (IC740). Y Check phase detector output pins (IC740 pins 3 & 4). Are there very narrow pulses (~50ns) at the reference frequency? (i.e. 5kHz : 200µs period 6.25kHz : 160µs period) *See Note below. N Check programming. Check serial bus when programming i.e. clock/data/enable activity (IC740 pins 18, 19 & 17).
C5.14 T854 Fault Finding M800 SL2 C Noisy synth; poor residual FM. VCO phase locked? 3-16V present on control line? N Go to B. Y N Correct DC V present on Q1 VCO? Check inductors, biasing resistors & Q1. Y Loop filter & components around op. amp. (IC750) OK? N Replace if faulty. Y Isolate audio modulation on VCO; still noisy? N Trace audio fault.
T854 Fault Finding M800 SL2 5.7.4 C5.15 T854 Drive Amplifier Key exciter & lock synthesiser. 10.5V on Q350 collector? 10.5V on Q355 collector? N 10.5V on Q315 collector? Y N 11.5V on IC350 pin 7? N Y Y >2V RF at VCO output? Check continuity of power rails & DC paths to Q365 & Q370. 13.8V on IC350 pin 8? Check VCO. Check regulators. N N Y >1V RF at R381? Y N Check attenuator pad #R517, #R518, #R519. Check lock det. path back to synth. IC740, IC750, Q325. N Y >0.
C5.16 T854 Fault Finding 5.7.5 T854 PA & Power Control M800 SL2 Normal operating conditions: Set RV320 (power adjust) fully clockwise; synth. locked; key Tx. Forward power Reverse power IC350 pin 6 IC350 pin 5 IC350 pin 7 = = = = = 4.7V approx. 0.7V approx. 2.02V 2V 8.63V Check Q410, Q420 & circuitry, LP filter. Y Tx delivering full power (>30W)? N 10.8V at L310? Y Check drive at SK310 >1.5W. N Y Check +13.8V at Q410 & Q420. N N Refer to Drive Amp. Fault Finding Chart.
T854 Fault Finding M800 SL2 5.7.6 C5.17 Audio Processor Key exciter & lock synthesiser. Connect 1kHz audio to external CTCSS input. N Does exciter modulate? Y Audio output at IC260 pin 8? Y Check audio path to VCO control line. N Check alignment of modulators. Y Audio output at IC260 pin 1? Check buffer IC260 pins 8, 9 & 10. N Y Demodulated audio frequency response flat between 50 & 300Hz? Y Audio output at IC260 pin 7? Check low pass filter stage IC260 pins 1, 2 & 3.
C5.18 T854 Fault Finding 5.8 To Replace The T854 PA Transistors (Q410 & Q420) M800 SL2 Caution: Failure to comply with the following procedure can result in failure of the device due to poor heatsinking, or worse, can endanger the health of the assembler if the beryllium oxide die carrier is smashed during assembly. Caution: As the location of certain components in the PA is critical to performance, it is important that any components removed or disturbed are refitted in exactly the same position.
T854 Fault Finding M800 SL2 Q410 Only: C5.19 Unscrew the transistor stud nut and remove the device. Remove any excess solder from the PCB pads with solder wick. Trim the tabs of the replacement transistor so that the device sits neatly on the PCB pads provided. Lightly tin the underside of the transistor tabs. Remove any excess solder to leave a thin, even layer on the tabs. Apply a small amount of heatsink compound (Dow-Corning 340 or equivalent) to the transistor mounting surface.
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T856/857 PCB Information M800 SL2 6 C6.1.1 T854 PCB Information Caution: This equipment contains CMOS devices which are susceptible to damage from static charges. Refer to Section 1.2 in Part A for more information on anti-static procedures when handling these devices. This section provides the following information on the T854 transmitter exciter: • parts lists • grid reference indexes • mechanical assembly drawings • PCB layouts • test points & options connections drawings • circuit diagrams.
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T856/857 PCB Information M800 SL2 6.1 C6.1.3 Introduction Product Type Identification You can identify the transmitter or exciter type by checking the product code printed on a label on the rear of the chassis (product codes are explained in Section 1.3 in this Part of the manual, and Figure 1.1 in Part A shows typical labels).
C6.1.4 T856/857 PCB Information M800 SL2 Parts Lists The 10 digit numbers (000-00000-00) in this Parts List are “internal part numbers” (IPNs). We can process your spare parts orders more efficiently and accurately if you quote the IPN and provide a brief description of the part. The components listed in this parts list are divided into two main types: those with a circuit reference (e.g. C2, D1, R121, etc.) and those without (miscellaneous and mechanical).
T856/857 PCB Information M800 SL2 C6.1.5 Variant Components A variant component is one that has the same circuit reference but different value or specification in different product types. Where two products share the same PCB, the term “variant” is also used to describe components unplaced in one product. Variant components have a character prefix, such as “&”, “=” or “#”, before the circuit reference (e.g. &R100).
C6.1.6 T856/857 PCB Information M800 SL2 Using CAD Circuit Diagrams Reading a CAD circuit diagram is similar to reading a road map, in that both have an alphanumeric border. The circuit diagrams in this manual use letters to represent the horizontal axis, and numbers for the vertical axis. These circuit diagram “grid references” are useful in following a circuit that is spread over two or more sheets.
