I don't know what happened with the attachment.? Yahoo messages can be very mysterious. I'd just googled for images of an OA95, and added one.? The chunk of schematic is the main bit.
You can check the OA95 (D4) by measuring some voltages with the power off, and with it on.
1)
With the power on, the 3V battery voltage shouldn't be significantly higher than with the power off.? If it is higher, the OA95 may be leaking.? You should see 5V at the cathode, and 3V or so at the anode - the end that connects to the positive terminal of the 3V battery, if it's not leaking.
2)
With the power off, you should see a voltage drop of 0.3V or a bit more, from the anode of the OA95 (battery end) to the cathode (RAM chip end).? Alternatively, measure the voltage at the supply pins of the RAM chips, and across the 3V battery.? If it's over 2V at the RAM chip supply pins, but a bit less than the 3V battery voltage, the OA95 is fine.
- I'm assuming you have a good battery.? If not, there could be a bigger difference in the battery voltage with the power off and with it on, which could confuse matters a little, but measuring the voltage from one end of the diode to the other, in each case, is still a good test. ? With the power off, it should be reverse biased and isolating the battery (cathode at a higher voltage than the anode).? With the power on, it should be forward biased, supplying power to the RAM chips (anode at a higher voltage than the cathode, probably by quite close to 0.3V).
The zener diode is a separate issue.? If the OA95 seems to be bad, replace it and see what happens then.
- Andy
AndyHornBlower