A8/A9
A8 Rectifier, Circuit DescriptionPower is supplied to the instrument through the A9 Power Line Module, which contains the line voltage selector, to the primary of transformer Tl. Three bridge rectifiers and one center-tapped secondary provide the rectified outputs.
Diodes CR1 through CR4 form a bridge rectifier that provides approximately 55 V for the
-40 V supply, part of the A18 Negative Regulator. CR5 through CR8 form a bridge rectifier that provides about 20 V for the -10 V supply and the -5.2 V supply, also part of the Al8 Negative Regulator.
Diodes CR9 through CR12 form a bridge rectifier that provides approximately 30 V for the i-22 V supply, part of the A8 Rectifier, and also the i-20 V and i-12 V supplies, part of the Al7 Positive Regulator. Diodes CR13 and CR14 form a full-wave rectifier that provides about 12 V for the i-5.2 V supply, part of the Al7 Positive Regulator.
The +22 V (STANDBY) supply is an 18 V three-terminal regulator Ul which has its common terminal biased at +4 V by Rl, DSl, and R2. DSl is an LED indicator that indicates the presence of +22 V. VRl and CR16 form a crowbar circuit for overvoltage protection. Fuse Fl provides overcurrent protection. The regulator Ul is also internally protected against short circuits on its output. The +22 V supply is on whenever the instrument is connected to an ac line outlet.
The instrument is also protected against line overvoltages by an input crowbar circuit consisting of VR2 and CR18. This crowbar causes the line fuse to blow if an overvoltage condition occurs on the line.
Filter capacitors and bleeder resistors for all the switched power supplies are located on the A23 Motherboard. The filter capacitors for the +22 V (STANDBY) supply are A8C6 and A6AlO C8. The location of fuses in the RF Section is shown in Figure 1.