Garmin GPS 155 Repair Manual

Also see for GPS 155: Pilot's guide addendum

Garmin GPS 155 Repair Manual Manual pdf 8 page image

The NiCad battery charger circuit is built around the Integrated Circuit Systems, Inc. ICS1700A rapidcharge controller. This controller uses a pulsed charging system, which is in effect when external poweris supplied through the rear connector. When the unit is off, the batteries are not being charged by theexternal supply. When the unit is connected to a wall charger, however, the batteries are trickle chargedat a constant current of 125 mA.1.2.3 RF/IF AssemblyThe RF/IF assembly consists of a dual conversion receiver, a frequency synthesizer, and a high precisioncrystal oscillator. The receiver consists of a ceramic RF filter, RF and IF amplifiers, mixers, and an IF fil-ter. The frequency synthesizer uses the high precision oscillator as a reference frequency for the phasedetector in the synthesizer. The resultant frequency is used in the mixer section to produce the first IF.After further amplification and mixing with a product of the crystal oscillator, the baseband IF is passedto the CPU Board for processing. The crystal output is also used for the system clock pulse. The RF/IFassembly is contained within a shielding fence/cover and connection to the antenna is made via a BNCconnector. The RF/IF supplies +5 volts to the antenna’s preamplifier through this BNC connector.The block diagram in Figure 4 below shows the interaction between components on the RF/IF Assembly.Figure 4RF/IF Block Diagram1.2.4 Interface Board and Data CardsThe Interface Board provides two-way data transfer capability between the Main Board and a data card.NavData® cards, available in sizes from 1 to 4 megabytes depending on the content/coverage area,allow for data transfer to the Main Board only. User data cards, with 768 kilobytes of flash memorydata storage, may be used to save user data/settings from the GPS 155 or restore that information tothe GPS 155. Address and data lines from the Main Board route through the Interface Board’s outputbuffers to the data card. A plastic race secures the Interface Board at the front of the unit and serves toguide the data card onto the 40-pin connector.NOTE: When servicing the GPS 155, user-defined waypoints, routes, settings, etc., may be saved on auser data card (010-10032-03) first. In the event these data are lost, they may then be restored fromthe user data card before the unit is returned to service. Refer to Appendix A of the GPS 155 Pilot’sGuide for additional information on user data card operation.5