LC II recapped but still white screen and boots in a while

[d3jsp]

Got an old LC II out of storage. It will turn on, the harddrive will spin and sit at white screen for ~30 minutes before the startup chime and boots from the original scsi drive. After that, if I leave the power on, I can reboot and it will chime right away and works perfectly. I thought this was an obvious cap issue.
Here is the strange part: Just replaced all 17 caps on the board here: https://recapamac.com.au/macintosh-lcii/ and it behaves exactly the same... When booting cold, it sits at white screen, chimes after 30 minutes, then boots.

There has to be some other caps on the board causing behavior this right?

 

[Plasticoat]

Is power supply tested and ok?

 

[d3jsp]

yeah, power supply is fine. 5V/-5V/12V. Plus, once the computer boots it works just fine

 

[d3jsp]

actually after recapping, now it takes exactly 19 minutes from power to chime and boot. Authentic old Macintosh experience

 

[cheesestraws]

Normally for those kinds of time scales I'd think it was something thermal, but that's perhaps a bit too precise for that. What's the tolerance around that 19 minute measurement / how consistent is it? Congratulations on finding a really weird failure mode!

 

[d3jsp]

It actually varies a bit depending on how long since it's been turned off! After several tests, fresh boot can take up to 22 minutes

 

[cheesestraws]

OK - so please be aware this is something in the nature of a guess - but this really does sound thermal to me. By thermal I mean something like - there's a solder joint somewhere that's got a hairline crack in it and therefore is a very high resistance, as current trickles through it, it slowly warms up and expands. This could even be something like on the back of the connector on the logic board where the PSU wire connects.

When you checked the voltages when the computer was just sitting there, where did you check them? On the PSU connector, or did you verify power to major ICs? What measuring equipment have you got handy?

 

[Zarwox]

Perhaps the machine is held in reset state during this time? Check the state of the RESET signal. A good place is pin 15 on EGRET U10 I think. While you are there also maybe check the +5V sense line pin 12.

 

[d3jsp]

If I am measuring the correct pin (the first one on the second row), it's always at 5V during white screen as it waits to boot

 

[d3jsp]

and this time it booted in 7 minutes while I was messing around with the multimeter, strange! It has never booted this fast before

 

[d3jsp]

and pin 12 is also +5V

 

[joshc]

Can we see some photos of the logicboard please?

 

[cheesestraws]

Sorry, second row of what connector, and pin 12 of what connector are we talking about here?

 

[Chuckdubuque]

Do you have a BlueSCSI or other SCSI emulator? Try booting from that to eliminate the HD. I've had long boot times from failing SCSI drives.

 

[Scott Baret]

Curious if it takes less time after a CONTROL-COMMAND-RESET reboot. I have an LCII in my lab that occasionally comes up to this screen and after a reset, it's fine. It has a working SCSI drive like yours and was recapped a few years ago.