Clock not updating with good battery

[captjon320]

I just ran into something that I haven’t seen yet, any help would be appreciated.

 

Mac SE FDHD, logic board had removable battery type.  Not the soldered battery.  Running 6.0.8 with a Blue SCSI hard drive.

 

I replaced the battery, no corrosion visible.  Cleaned machine and rebooted.  Everything normal, except the clock/date  will not update.  I can change time/date but the seconds do move on the clock, they stay at 00.  I could come back three days later and the clock/date will be exactly the same as what I set.  Also, all the other settings I may have changed will not fall out (mouse movement speed, etc) they remain to what I set.  After Dark will not activate, I assume since the clock isn’t being recognized.

 

I have tested the voltage with machine off and also on (under load). I have good voltage both at the battery and also the positive trace that runs down to the chip.  
 

I’ve never encountered this before, any help would be appreciated.

 

 

[hideehoo]

Sounds like a bad RTC chip or crystal.

[captjon320]

Thanks, I was unfamiliar with the RTC chip, I’ll check it when I return home next week.  
 

The little reading that I’ve done about the RTC is that is was a custom part for Apple and there aren’t any replacement parts available,  unless a person can pull one off another board.  Does that information sounds correct?

 

I appreciate the hell and will update this once I can take a look at it.

[Daniël Oosterhuis]

On 2/19/2021 at 6:47 PM, captjon320 said:

The little reading that I’ve done about the RTC is that is was a custom part for Apple and there aren’t any replacement parts available,  unless a person can pull one off another board.  Does that information sounds correct?

 

There is work being done on an ATTiny85 based drop-in replacement, by fellow member @quorten. You can read about it here.

[captjon320]

Thanks to everyone for their help with this.  The RTC chip looks great on the board with all the legs in tact,  also there has not been any battery leakage from the old soldered battery that I removed when I first obtained the Mac.  Therefore, it must be a crystal inside the chip that has gone bad.

 

Other than using the above mentioned ATTiny85 replacement that is being developed, it looks like my only other choice is to find a donor board and remove this chip.  Unfortunately, I don’t have one.  If anyone has a parts board and would like to remove the chip, I’d be happy to pay for their time and shipping to me.

 

Thanks again to the community,

 

Jon

[Arisotura]

I don't know if there are many parts boards with good RTC chips on it -- part boards are generally Maxell-bombed, and the RTC chip seems to always be near the battery holders, so it's one of the first things to be destroyed.

[quorten]

@captjon320 Note that the 32.768kHz quartz crystal (approx. 12.5pF load capacitance) is outside the RTC chip, with radial packaging.  Based off of my personal anecdotal evidence (for only a single incident, and a wrist watch at that), radial packaged quartz crystals tend to go bad when the bonding on the legs to the quartz crystal inside loosens up, lazy-boy's fix (i.e. me) is to just wiggle around the package until electrical connection is re-established and then glue it to a support to hold it in that position.  But of course, the real solution is to solder in a replacement proper.

 

My guess is that the RTC chip is just fine since you've noted that the PRAM read/write functions still work as intended.

 

Tactfully I must mention, the ATTiny85 variant of the RTC replacement chip does not use the crystal oscillator at all, it's all based off of its internal RC oscillator.  So although it's a bummer in terms of timing accuracy, well that's less discrete electronic parts to worry about and it probably makes no difference when using network time syncing.

Edited February 23 by quorten
Minor clarification

[captjon320]

@quorten I appreciate the information as I didn't realize the quartz crystal was actually outside of the rtc chip.  It is nice to see another Minnesotan on the forum, shoot me a pm as I am interested in your ATTiny85 variant also and would like to talk to you about it more.

 

 

[ScutBoy]

There's a few Minnesotans here...