Elonex 386 battery (again)

In message , Graeme writes

It appears to be a socketed chip that contains a lithium battery.

Just a question of carefully pulling the old chip out and plugging a new one in, but whether a replacement with a good battery would be easy to find, I don't know..

You may have to change the whole chip (I posted about this previously).

But since yours is socketed the phrase "piece of piss" springs to mind.

If you can't boot the PC with an inoperative RTC, you may not be able to use the PC to switch on a new chip.

Alternatively, you might be able to just add a battery in parallel. You'd need the spec sheets for that.

Am 30.05.2018 um 16:51 schrieb Graeme:

Might be that beast:

Your chances to get a working one are very close to zero. Sorry.

Can anyone explain in one sentence what the big idea about having the battery integral to the chip was ? Apart from the most egregious example of inbuilt obsolescence I can think of ?

I asked that 27 years ago when I changed the Dallas RTC on a mobo then which had failed after 18 months, and didn't get a sensible answer.

If you Google the chip number it looks like this is it and also some page a bout changing it. I had a quick glance but seems like it may have been repl aced by another compatible chip so may be easier to replace. Wonder if look ing at the data sheet for the chip you can determine the power pins for the battery and replace it with a button battery or something.

In message , Jethro_uk writes

OK all, very many thanks for the comments, again. This appears to be the spec sheet, with the power pins top right and bottom left (Vcc/GND), presumably Vcc +ve and GND being -ve.

Have I understood this correctly? Assuming I can get the whole chip out, I solder battery power (button, or 3 x AA) to those pins, pop the chip in, job done?

Or, even with new battery power, how much will I have to reset? I can see I will have to input details of the drives, but beyond that?

Finally, never having removed a chip, do I just grab it and pull gently?

Its in an IC socket, so just lift it by working from both ends to prise it out. If replacing with a new one, you may need to bend the pins in a bit on the new device to get it back in the socket. (do this by gripping firmly and pushing all the pins on one side on a firm surface at the same time to bend them in a bit)

Vcc pin requires 4.5-5.5v and consumes 15mA, too much for a lithium coin cell to last long.

I didn't see which pin to connect a cell to. You could also use a rechargeable charged from the +12 line, regulating it to 5v to run the IC. Flip the Vcc pin out to do this as there would otherwise be other loads as well.

NT

Don't forget earthing strap on wrist ...

It is going to be a bit of a fiddle but a Schottky diode in series to isolate the pin from the rest of the board a resistor to trickle charge

Replacing the chip may or may not work. According to the data sheet, they are supplied with the oscillator turned off (to save the battery) and need a specific code loaded into a register to start it.

Powering it as above may, but ity is possible that the chip defaults to not running the clock after loss of power and a completely drained battery.

Many PCs will not be able to boot into DOS until it is running and will not start it themselves, without a manufacturer's setup disk.

SteveW

that'd work if the chip runs ok on 3.6v. It's well outside mfr's spec though. Will they?

yeah keep the chip not bending over to one end, which it tends to

NT

Nope, that isnt what keeps the data in the cmos.

I think this chip is a replacement for the popular Motorola MC146818 realtime clock chip. The key phrase on the datasheet is "Drop-In Replacement for PC AT Computer Clock/Calendar". There are other chips that do that job which are still available - eg

I think I have one lying around never used, though it's probably 15-20 years old. I can check next week - if I can find it and it's the right one, you can have it.

If the RTC clock is not running, doing the hotswap trick may be enough - I don't see anything that would cause the chip not to respond, though it might not keep time out of the system since it needs the crystal for that.

Someone got in touch about an RM Nimbus 386 the other day - apparently to boot from HDD requires the BIOS setup program which was provided on a floppy disc - it appears lost. So the caution is to backup your CMOS RAM if you can.

If the system has a ROM BIOS setup program (can you go into setup without a floppy/HDD?) then chances are good you can reset the RTC chip from there.

Theo

Not sure that last bit sounds right... if it won't boot, then how is it going to use the setup disk?

Some old machines needed a setup disk to set things like HDD parameters (there was not always a direct interface built into the bios to allow pre boot setup), but with those you could usually still boot from a floppy.

I have had a portable go down that way (not worth taking apart to fix) and it would recover if you went round a loop of plugging it in and allow the boot to fail then wait 10 minutes and reboot and the CMOS could then be reset manually. Boot time was 00:00 1/1/1980

My experience was that they just show a daft time. I get emails from someone who is usually stuck in Jan 1980 for this reason.

ISTR It goes into torpor for 100ms after power is restored and when its input voltage drops below 4v to prevent spurious write cycles. When it is in this state write cycles are ignored but read cycles are permitted. I have no idea how much current it draws though.

Especially when done by someone inexperienced.

Two small L shaped things as levers applied together, one at each, end.

Allen keys?

Because in the era when this PC was designed, one chip replaced

QED, less power, less MB space needed.

The spec says the battery lasts 10 years which means it will outlive the useful life of the PC.