Recapped Color Classic does not power On from keyboard

[nvdeynde]

I recently recapped 2x Color Classic logic boards. One of them works well and turns on immediately from the keyboard, with new Pram battery installed.

The other one remains dead, tested in the same machine.

I measure around 3.5 volts on the ADB ports, so it gets power from the Pram battery, still refuses to come to life. I re-checked all the replaced capacitors and everything is fine, no shorts, broken traces or faulty caps ( ESR tests are fine ). I also cleaned the contacts where it meets the wiring harnass.

Both boards were non-working before I recapped them, however why does one come to life and the other not ?

The zero visible damage to the PCB of the non-working board.

I already tried the trick of sliding the board quickly in and out with the power switch on to no avail. As soon as it slides out, the classic powers on and hard drive starts spinning, but when sliding it back in fast doesn't help. The screen is gray, HDD keeps running, when you power it off, it's dead again, no start from keyboard.

Leaving it in the Classic for 24 hours with power switch on also doesn't work.

The Analog board of the color classic is also completely recapped so we can rule out this as well.

Any idea's to solve this ?

 

[uniserver]

plug it in

turn the power switch on,

hook up keyboard

slide the logic board out and then in quickly…

start tappin power button on keyboard

it should come on..

 

[Macdrone]

Check traces. Did you try washing in a washing machine? Hot soapy water on the bottom rack breaks up and removes alot of stuff that you just cant see with the naked eye. I would eyeball the traces by the adb port tho with a magnifying lens.

 

[nvdeynde]

The board was fully cleaned with pure Isopropanol on both sides. I checked the complete PCB under a magnifying glass, didn't find any issues.

I also tried the procedure of quickly sliding it in and out with the power switch on, multiple times to no avail.

Eventhough I measure power from the Pram battery on the ADB ports, it does not start.

Maybe the ADB chip or PMU is dead.

I tried replacing the Roms as well from a spare known good set to no avail as well.

I got the board from a fellow collector in non-working condition even before recapping, so I have no idea what happened with the board before I got it.

It look beyond repair as far as I'm concerned. As far as I know there is no other way to power it on as through keyboard.

It's regrettably not like a Mac IISi or IIFx that has both keyboard start and a power button at the back.

 

[uniserver]

I have seen some of the caps on the bottom knocked right off. Check the bottom closely for little missing SMT caps/resistors.

 

[uniserver]

did you ever end up getting this to work?

 

[nvdeynde]

No, I regrettably haven't been able to repair this one. My best guess is a faulty PMU or ADB Controller.

These soft-start boards are very hard to troubleshoot and without any spare parts from a scrap board there isn't much one can do.

 

[James1095]

Isn't the power button connected to a separate wire in the keyboard port rather than using ADB signalling?

 

[mcdermd]

interfacebus.com[/url]"]Soft Power [Pin 2]On a Macintosh with software power control, the machine can be turned on by an ADB device.

This is accomplished by momentarily connecting pin 2 on the ADB connector (reserved) to pin 4 (ground).

Pin 2 should be kept grounded until pin 3 (+5 volts) comes up to power, letting you know that the machine has actually come on.

Some Macintosh machines do not have soft-power capabilities; on these machines, grounding pin 2 will have no effect.

I had a IIcx repair with a corroded trace between the ADB ports on pin 2 that prevented soft power on one of the ports.

 

[nvdeynde]

I did check the traces and the ADB ports had +5 volts, nevertheless no power on.