Hi, I need help to find the parameters of an external battery. This motherboard has a 3-pin connector for the CMOS battery, but I don’t know the voltage.
Very similar model, but there is no info about a battery voltage.
I would use a 4.5v source like 3 x AA, most 286, 386, 486 used 4.5v externals. There were a few that used 6v (4 x AA) but they are not common.
If 4.5v does not keep time/clock running THEN try 6v. Use a ohmmeter and find which pin is ground for -, the other end pin should be the +.
Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun
Thank you!
GinnunGagap wrote on 2024-08-04, 17:51:Very similar model, but there is no info about a battery voltage.
There is - but it needs some navigating, and even then it doesn't leap out of the page...
Click on the chipset (82C836) which takes you to
https://theretroweb.com/chipsets/239
Then click on Documentation and you get a link to the device data sheet.
On page 32 of the 205 page document there's a circuit diagram with a suggested circuit to manage the Vcc supply to the chip set so that the battery doesn't end up trying to power the rest of the motherboard when the mains power is switched off.
Personally I would look at the PCB near the battery connector and if I saw three diodes in series, I would (a) trace the first diode back to the connector to identify the positive terminal, and (b) connect 4x AA batteries to the board.
The photo of the motherboard isn't that sharp, but if the battery connector is to the north of the power connector, then it's possible that the three components to the left are the three diodes, and the two transistors to the south, between the power and riser connectors are probably the two 2N3906 transistors shown in the circuit diagram (used to "connect" the +5V from the PSU to the 82C836.
Thank you! Here is the zoomed-in photo.
