2.1 Battery Backup Battery backup is actually more complicated than it might first appear, as it depends on a good system reset (see section 3.1 for details) in order to function properly. The actual backup circuit consists of a battery (3V - 3.6V Lithium), a 10K resistor (R97) for checking standby current (see below), a "steering" diode (D7), a filter capacitor (C59), and a transistor/resistor/diode combination that acts as a steering diode. This combination may be missing on older board revisions, and must be installed (see section 7.1) to prevent data corruption due to a significant difference between V cc and the amplitude of the data buss. SRAM standby current should always be checked.
While the unit is off, check the voltage across R97. If the voltage is higher than 80mV (specification, although a 1 to 20mV range is more normal) then a problem exists. Usually it indicates a bad (or simply wrong) SRAM, or a short somewhere along the MEM PWR line. Note that for a short time Sony 58256-PM (high power) SRAMs were being installed at the factory, causing batteries to drain in about 1 year. They should be replaced with low power versions (58256-LP) when found, in order to eliminate excess battery drain. We are currently using Hitachi 62256ALPs as replacements. CAUTION: Danger of explosion if battery is incorrectly replaced.
Replace only with the same type or equivalent type recommended by the equipment manufacturer. Battery Manufacturer: Tadiran Type: TL-5101 Rating 3.6V 2.2 PUP Circuit The PUP (quiet Power UP) circuit is designed to prevent the unit from making noise during power up. Note that this circuit will not be present on the earliest main PC boards. The circuit utilizes the RESET line (section 3.1) to control the power supply lines to U20, which is the final active stage before the output jacks. Since both rails operate similarly, we'll only take the time to explain the operation of the + rail. During power up, the RESET line is held low until the regulators are fully functioning.
At this point, Q11 is turned off by RESET via R104. This has the affect of turning off Q10 by allowing the base of Q10 to pull high via R101. As soon as the reset line goes low, Q11 will turn on, pulling the base of Q10 lower. Q10 is now biased into saturation, allowing roughly +12V to be fed to the op- amps. C65 is provided for extra filtering. The - rail consists of R99, R100, R105, Q12-Q13, and C64. Diagram 2 HR-16/HR16B Service Manual 1.00 2