VOGONS


First post, by kohellus@gmail.com

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Hello,

Was wondering, i have an old small form factor 286 motherboard that i was sometimes back asking "how many times a 286 cpu can survive being turned on in the wrong orientation".

Have been tryin to troubleshoot it not posting up and it did have some nasty varta menace but it seems that, testing with post card all the voltages goes through, reset works and 5 volts are present in the cpu, oscillator and memory. Though iam not an electrician...

But something weird is happenin in the battery circuit. Varta is removed but the plus side of that should go through a transistor and maybe some resistors? But theres no connection, maybe traces but that transistor dont have a ground anywhere and the battery plus side is getting 2.3 volts when powered, although that transistor is getting nothing. The second transistor (side by side) is getting 0.1 volts but it has a ground connection. I think those are dead but can it drown the whole system? I did read that some old motherboards wont turn on without a working battery?

Thanks in advance again!

Reply 1 of 2, by Jo22

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"I did read that some old motherboards wont turn on without a working battery?"

Yes, happens with old 68k Mac all the time. They need a push on the reset buttons, too. NVRAM, Parameter RAM etc.

On old ATs, the clock chip contains the BIOS parameters. They're stored in the unused parts of the RTC's (Real Time Clock's) SRAM.
So if the on-board clock has no power, that SRAM is dead.

And some BIOSes simply won't boot with an inaccessible SRAM.
These BIOSes require the SRAM to hold the configuration data, even if the SRAM was empty during power up.
If it was empty, I assume, a routine would stupidly upload default settings and then the BIOS or CMOS Utility would read them back as if everything was normal.

Other BIOSes just load the default parameters into RAM from within their BIOS ROM chip.
Those may POST and report an RTC failure.

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