Chuck(G)
25k Member
It probably was intended as a parity check, then. Congratulations!
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JX30 VL-Bus Motherboard issues
- Thread starter Lutiana
- Start date
Ok, another question about this board. I have noticed that the RTC won't seem to maintain the date and time accurately. It seems to be way off pretty quickly after I set it.
It appears to only happen when the system is turned off.
Now one reference somewhere to this board said the external battery connector is for a 4.5 - 6v battery, I have a 3v battery plugged in. Could this be causing this? Or do I have a bat RTC chip?
It appears to only happen when the system is turned off.
Now one reference somewhere to this board said the external battery connector is for a 4.5 - 6v battery, I have a 3v battery plugged in. Could this be causing this? Or do I have a bat RTC chip?
Chuck(G)
25k Member
How far off is "way off"?
External batteries on these things tend to be 6v or so. There is usually a series-pass transistor and a diode or two that drops the battery voltage by a volt or two. I don't think that 3v is enough.
Another possibility is that the 32KHz crystal is flakey. Chances are that your MC146818 is fine.
Well I set it this morning and left it on all day and the clock is spot on. I just turned it off and will turn it on in an hour or so and see how far off it get, but it seems to be quite a bit off.
Once I verified this I will have to switch it out with a 6 volt (4 AAA) holder, and verify that the problem goes away.
kishy
Veteran Member
Edit: nevermind this completely irrelevant post, my head was obviously in other places.
That's just weird (that you're having problems, that is). Since you did the battery mod directly to the RTC module, which if it is indeed a DS1287 clone has a 3V cell inside, it should be working fine with 3V (since that's the battery that's been in it all along, even when it did work).
I don't know if it's relevant to the situation, but when you did the RTC mod did you make sure you fully broke the contacts to the pre-existing battery inside the RTC module? I don't know much about lithium batteries but if it's getting that "one bad cell drags down the good ones" effect going on it could be the problem.
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MikeS
Veteran Member
I think you're in the wrong thread ;-)
kishy
Veteran Member
You're 100% correct.
Same OP, same subforum, motherboards of similar vintage, discussion that at first glance appeared the same. I hope I'm not the only one who can easily justify that mistake...
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Wrong thread :D I did that with the other 486 I was working on, and that one works just fine.
I am thinking that my problem here is the battery I have on this board is not big enough, at least that's my gut feeling.
Right, so as soon as the power is turned off the internal clock stops completely.
I turned it off at 5:01p and back on at 6:01p and the clock still says 5:01p. Only the clock is affect, the BIOS settings are maintained just fine.
Does this sound like under voltage on the battery?
I turned it off at 5:01p and back on at 6:01p and the clock still says 5:01p. Only the clock is affect, the BIOS settings are maintained just fine.
Does this sound like under voltage on the battery?
Chuck(G)
25k Member
Could well be that the voltage isn't high enough. The MC146818 is rated for 6v operation, so you're not going to roast anything by trying it with 6v.
Fixed!
6V was apparently the magic number. I soldered a second AAA holder in series with the first, then added the 2 extra batteries and tested the voltage, got 5.2V, so I replace the original 2 batteries and got a 5.9V.
Ran the same clock test as before and this time it incremented the clock just fine.
Sweet, now I think this board is 100% functional, and is pretty darn quick. All I need is the memory I ordered to up the RAM to 64Mb and I'll be done.
Thanks for the help!
6V was apparently the magic number. I soldered a second AAA holder in series with the first, then added the 2 extra batteries and tested the voltage, got 5.2V, so I replace the original 2 batteries and got a 5.9V.
Ran the same clock test as before and this time it incremented the clock just fine.
Sweet, now I think this board is 100% functional, and is pretty darn quick. All I need is the memory I ordered to up the RAM to 64Mb and I'll be done.
Thanks for the help!