First post, by Gabriel-LG
Recently I received a cute Philips P2230, 286 12MHz, 1MB, CGA. Complete with monitor, mouse and keyboard.
It had a depleted Dallas RTC, and as an effect it could not boot past the BIOS.
Since the RTC was not socketed, I desoldered it and placed a socket in the mainboard.
I did not have time to do the battery mod on the RTC just yet so I took the board home again for some testing.
First I wanted to check if the RTC and mainboard had survived (the desoldering was quite traumatic).
So I started the PC with the RTC in place. It worked, just as it did before (phfeww).
In preparation of the battery mod, I wanted to know what to expect if RTC would not survive surgery.
So I removed the RTC and started the PC. I think it gave output on the monitor, although I am not sure because I was quite distracted by the smell of smoke 😦
Upon inspection, the tantalum capacitor over the -12V had burned out. I had a similar capacitor, only not SMD like the original, so I improvised a temporary fix while ordering new capacitors.
With the capacitor replaced and the RTC placed back, the machine is working.
Later on, the battery mod was successful also.
It just keeps nagging me, that I cannot think of any reason why the -12V capacitor would burn out if the RTC is not present.
- The capacitor was on the other side of the board, so it could not have been damaged by heat.
- The RTC does not use negative voltages (so not interaction with -12V)
- The BIOS does not usually control the power stages in machines of this era.
My new capacitors are in now, and I am tempted to repeat my experiment of running without RTC. But I am afraid it will kill something if the tantalum burns out again.
Does anyone here have a clue as to why the -12V tantalum would burn out if the RTC is not present? Or have any experience in running a PC without having the RTC installed?
If not, would it be safe to repeat the experiment to rule out coincidence?
