can hear the fan but no boot

[frameworker]

Hi everybody,

after more than 20 years my classicII seems dead. But I hope it's something which I can repair, but I need a hint maybe:

The symptoms are:

During running the Mac, it's freezing. Press the reset button had no effect, that's the first time that this happens.

After restarting the Mac, I can hear the fan, but no startsound, no screen and no access to the disk or floppy.

Inspecting the logic board shows no corrosion, the battery was changed a few months ago, there are also no visible damages on the analog board.

What should I do next?

 

[360alaska]

Start with logic board capacitors if you haven't and then go from there. If you have all ready recapped that guy then I would look at ram...

 

[Schmoburger]

Classic II's have terrible capacitors... Whilst there may not be corrosion on the board, they could still have leaked and the goo could be shorting contact pads. Whilst a cursory glance may show the board as looking good, a closer look may reveal leaked electrolyte which may show as stickiness or a dry waxy film. One way to temporarily get it going may be to scrub firmly all the IC legs and pads and other electronic contact points with a toothbrush and see if the board becomes functional again. This has revived a few of my boards temporarily... this being said, if it does, you almost certainly have bad caps and the problems will be recurring and eventually the cap leakage will damage the logic board, sometimes irreparably if left too long. Even if the caps arent leaking  (i'd be surprised if some arent by now on a Classic, SE/30 or ClassicII logic board), they may still be open, shorted or otherwise out of spec and affecting the functionality of the asembly.

In short, I would thoroughly clean the board and then remove all the old electrolytic surfacemount caps ASAP before they leak anymore and have the board recapped.

 

[frameworker]

Hi,

thanks for fast reply.

I will try the toothbrush. And you are sure, that's no problem with one of the fat capacitors on the analog board?

 

[Schmoburger]

Hmmmm I won't rule A/B issues out entirely, however the radials on the A/B tend to be a little sturdier than the crappy little cheap surfacemounts that Apple used on the logicboards.

A lot of the time failing A/B cap issues will manifest themselves as video problems such as wiggles or waves, and/or electrical intereference, and they tend to fail a little more impressively and suddenly... usually with a nasty stank, unpleasant crackling and some scary smoke, and concurrent with a screen that suddenly goes bonkers and dims out.

I'd be fairly confident in saying that the ones on the logic board are the culprit. It is almost guaranteed they are leaking or out of spec as every single one of the half dozen Classic and Classic II logic boards I have have had cap issues. Replace them and it will likely come good again, however it wouldnt hurt to also replace the AB caps soon as they are getting on 25 years old and they are realistically rated for around 1000hrs of use at 85 degrees celcius. Whilst they may never reach that temperature and are likely to therefore last longer, the main point is, they do have a finite service lifespan.

 

[notcrazy_iminsane]

I'd replace the AB caps as a precaution and to prevent future issues.

My bet would be to recap the logic board and make sure it gets a good scrubbin'. Also make sure you don't have the Maxell bomb ticking away in there. https://68kmla.org/forums/index.php?/topic/17086-warning-exploding-maxell-pram-batteries/ Even if it isn't a red Maxell, I pluck them out as soon as I get my hands on the boards.

 

[Schmoburger]

I'd replace the AB caps as a precaution and to prevent future issues.

My bet would be to recap the logic board and make sure it gets a good scrubbin'. Also make sure you don't have the Maxell bomb ticking away in there. https://68kmla.org/forums/index.php?/topic/17086-warning-exploding-maxell-pram-batteries/ Even if it isn't a red Maxell, I pluck them out as soon as I get my hands on the boards.

Definitely good advice on both accounts... Even if the AB caps havent yet failed, one day they will, and you don't want electrolyte spewed all over the surrounding area when a cap does rupture as you will have to clean everything to be sure prevent damage.

As for the batteries, whilst the Maxell cells are by far the most nasty, and are really the only ones ive come across that explode violently, any other old or flat battery can degrade and leak too, and this is just as damaging as an exploded one if left long enough. Realistically even if the battery keeps time, you should still replace it as most would be 20 years old or more, and even Varta ones, which are known to hold a passable charge for nearly 30 years and are considered by many to be the best of all, only have a recommended shelf life of 10 years. The batteries will have a date code stamped on them and if that code says the battery is more than about 5 years old it's good practice to replace it or remove it if you arent worried by the PRAM resetting itself after every shutdown (this last option isnt applicable to most NewWorld Macs as they require a PRAM battery to power on, and the PM9600 is temperamental if it has a flat or no PRAM battery).