Agilent Technologies 2948, 2712A manual Troubleshooting Memory Backup Battery

Service Model 8904A

3.Partially remove the A2 Digital Assembly as follows. (figure 6-1,Main Deck Assembly-Top,may be helpful.)

a.Unplug all connectors on the A2 assembly except the two soldered-in coaxial cables. (To remove the front-most keyboard ribbon cable, lift up on its retainer and push the retainer forward.)

b.Remove the single Torx screw securing the A2 assembly.

c.Carefully lift the A2 assembly from the seven plastic holding posts by compressing the small holding tangs with needle-nose pliers, and pulling the board up until the printed circuit board is free from the posts. Carefully rotate the board upward (hinging it from the left side as you face the front panel) until it is vertical. This should allow access to both sides of the assembly.

		I		=	- 1	BATTERY BACKUP RAM 1
		*5Y(F2>
								TO EXTERNAL
					1901-88BB			POWER SUPPLY
		R25	13		P	I
4;							'l"	1 2 8
		1.96K
+sv	8I	>
	(F2		1+
,L6.81K
					.7K

~~~

Figure 8-12.1Partial Schematic of A2 Digital Assembly Showing the Battery Backup

4.Refer to Figures 8-12.1and 8-12.3 for serial prefix 2942A and below or 8-12.4 for serial prefix 2948A and above. Rig up a temporary backup supply as follows.

a.Temporarily solder one lead of a 10 kR resistor to the lead on the "+', end of capacitor A2C5. (Solder on the component side of the printed circuit board.)

b.If a power supply is used (instead of a second battery), set it to approximately 3V then switch it completely off. Do not simply turn its voltage down to OV, or the 10 kR resistor will load down the backup.

c. Solder the other lead of the resistor to the "+"output of the power supply (or the temporary backup battery).

d.Solder the "-"output of the power supply (or battery) to the other lead of A2C5.

8-48.2 Troubleshooting (Memory Backup Battery) rev.15DEC89