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Might Not be relevant, ... since applies to the 4274a,? but:
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Just noticed an Hp Service Note in the Hp 4274a LCR manual (4274a-12) :
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" Improvement for Memory Backup Battery "
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-- about swapping out the original Schottky diodes (1901-0518) for? more common(?)
Si diodes ( 1901-0025 ), due to degradation of the Schottky diodes over time, causing the Memory backup Battery to discharge faster.?
Found in the Sept. 1980 4274a Serv. Man., pg. 2 for instruments having Opt. 003.
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Given that Hp used common designs in many instruments, ... might want to consider.
rick
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On Sun, Nov 21, 2010 at 10:11 AM, tss_steve_990 wrote:
I am really unclear, based on the schematic how the battery could cause
problems storing the open and short compensation constants in the permanent
RAM once the power is on. According to my understanding of the schematic,
when the 5 Volts is present (power good) Q3 saturates and shorts out the
blocking schottky diode CR1 and that puts 5 Volts on the U12 D4364C-15L
Memory chip. At the same time it charges up the battery thru the series 470
Ohm resistor.
The battery is 2.6 Volts with the unit off and 3.3V while it is on ...
