Atari TT clock precision

[moulinaie]

Hello!

 

I'm testing the precision of the clock in the Atari TT.

It looks like its precision is really bad!

I set it precisely one hour ago, and now the difference is 30 seconds!

 

30 seconds / 1 hour = 0,8%

 

Have you experienced the same or is it my particular TT that has problems?

It's not a question of battery as the test has been made with the TT running during the whole hour.

 

Guillaume.

[ParanoidLittleMan]

I guess that it's question of computer age. Maybe replacing crystal Y400 (32768 Hz) ? Or U402, U401 ..

[guus.assmann]

It may very well be that it can be adjusted.

On the much older MegaST, there's an adjustable capacitor.

And the same on a MegaSTE.

For these 2, I have a bare board and had a look.

For the TT, I'm not sure. But it can very well be the case. (Check the schematics)

If you can't find it, let me know and I'll try to invest some time to find out.

 

And only if this fails, replace the Crystal. (Not 100% riskfree, adjustment = lower risk factor.)

 

BR/

Guus

[guus.assmann]

Hello Guilaume,

 

Just now, I've checked the schematics for the TT.

It uses the MC146818 clock chip.

And an external clock generator, using a 4069 chip, U402. Only 2 gates A and B are used.

Using this C-Mos chip gives a lower power consumption than having the MC146818 do the oscillator. (It can)

The capacitor C408 is to be made adjustable.

Crystal is Y400.

 

BR/

Guus

[moulinaie]

Thanks for the infos !

By the way, I have another question:

on another TT the clock seems to be better.

But on this one, when the computer is OFF, the clock and date are saved but don't advance!

When I wake up the TT again, I get the time when I powered it off.

 

Can it be a problem of battery this time? Not enough power to make it run ?

 

Guillaume.

[ParanoidLittleMan]

You did not check battery ? In computer old some 25 years. Omg.

[moulinaie]

You did not check battery ? In computer old some 25 years. Omg.

I did : the old one was dead. I tried to change it with three accumulators 1,2V but I don't know if they are strong enough..