Lithium battery hack: 2 x AAA instead of coin battery?

[orange]

What about that little potentiometer for precise adjusting of clock speed; does it help for making clock more precise and how can one use it? (it would be hard to just rotate it a bit, measure time, rotate it more.. and so on)

[Zac67]

That's an adjustable capacitor used for fine-tuning the filter for the crystal. The crystal is a very cheap piece of quartz, not running a stable frequency, but rather a whole bunch of different frequencies. The one you need for the clock is then filtered out - because every crystal runs its own frequencies, the filter needs to be adjustable. Due to this low-cost method the clock's usually not very acurate (temperature changes, ...).
Turn right for making the clock run faster, left for slower. A very careful turn will make up for 5-20 seconds a day.

[Castellen]

@dnelsonfl:
From the limited detail in the pictures, the damage doesn't look too bad.  Or you've made a really good job of cleaning it :-)

The address latch, U177, is often the cause of the system failing to see the RTC.  There are also tracks and vias under U177 which can get corroded open circuit.
I've written a full fault finding and repair guide here:
http://amiga.serveftp.net/hardware_repair.html

All you really need is someone who can carry out some SMD soldering for you.  The continuity measurements you can probably make yourself.  I get the impression you're a little more electronically skilled than the average joe :-P


@orange:
As mentioned already, the trimmer capacitor is used to fine tune the 32.768kHz crystal oscillator in the Commodore factory as the crystals used aren't overly accurite.  I think they're 20ppm or less stability, from memory.
The frequency also drifts as the crystal ages.
The best way to adjust the oscillator is by using a frequency counter or decent oscilloscope.  It only takes a few seconds to do with the correct equipment.

[dnelsonfl]

@Castellen,

From the limited detail in the pictures, the damage doesn't look too bad.  Or you've made a really good job of cleaning it :-)

The damage actually wasn't too bad, and I did work at it to clean up what little there was. It's an important lesson that only a little bit of leakage was enough to kill the RTC. Too bad this 4000 and me didn't meet earlier. I could have prevented it altogether.

Your guide was very useful. I did run through checking all the connections it specified, and everything looks good. I found this company ChipQuick that gives out free samples of its SMD removal kit. I requested one. If the kit does indeed make it easy to remove SMD chips safely and easily, then all I have to consider is practicing on replacing it. Maybe they have a kit to do that easily, too. In a few months I might just attempt it.

-David

[Castellen]

That ChipQuick site doesn't seem to be working for me.
All you really need is to be able to remove the device (U177), which is simple enough.
It's a fairly large pitch, so you can easily get away with hand soldering on a new one.
I've also written guides on SMD soldering, you might find this one in particular to be of use:
http://amiga.serveftp.net/Replace_SOIC.html

[dnelsonfl]

The SMD removal kit arrived yesterday. Your instructions make it look fairly simple, so as soon as I find a suitable replacement chip for the U177 I'll be on my way.

All I've found so far is a Texas Instruments SN74HC174D in the States. It looks the same as the Farnell part on your guide, except it uses the term "clear" instead of "reset". Clear is a reset, right?

-David