Wierd Issue: Hard drive spinning down on LC II

[jack]

So I waited too long to recap (one of) my LC II's. I was using it the other day when the speaker started crackling as I was using it... uh oh.

Pulled it off the stack and pulled out the caps. Ordered new ones, they came today and I recapped it.

After recapping, the sound is nice and crisp again, but the hard drive now spins down a few seconds after spinning up during booting. It repeats this, then tries to boot off the floppy. Seems really odd, the recap was very smooth (no lifted pads etc.) and I cleaned it pretty darned thoroughly. Any ideas?

I've tried multiple known working SCSI drives, and it worked before recapping.

 

[BadGoldEagle]

First of all, are you 100% sure you got the polarity right when soldering in the new caps? It happened to me once, one cap was mounted backwards...

Then, if the logic board seems fine, the PSU might be weak. Check the PSU voltage with a MMU. Mine's currently outputting +0.6V on the +12V rail...

I need to recap it too!

Mac LC PSU pinout
1 Ground  Black
2 Ground  Black
3      Not Used 
4   5+ V     Orange
5  12+ V    Yellow
6      Not used 
7   5- V     Blue

 

[jack]

Yep, quadruple checked polarity. They're tantalum capacitors, so I think they would pop if I got this wrong as well.

PSU is OK, 5 V measures 5.04 and 12 V measures 11.78. I can also use it to boot my other LC II successfully.

 

[bibilit]

Hi,

Can you check outputs at the HD molex connector ? pretty easy in the LC as the molex is pretty easy to check in the Logic Board side.

Also, any shorted capacitor ? happened to me a couple of times.

 

[EvilCapitalist]

If your drive is a Quantum it's likely just stiction and it's a pretty common issue with the older drives out there.  There are a whole bunch of threads that mention it (just search "stiction") but this thread is one of the more detailed ones.

 

[bibilit]

Yes, but he has been trying other good drives as well.

I've tried multiple known working SCSI drives, and it worked before recapping.

 

[jack]

Yep, and both the drives I tried boot just fine in my other LC II.

bibilit: I checked the power at the HD molex connector last night, and while I don't remember the exact values, they were pretty close to 12 V and 5 V. I also poked around the board checking for connectivity on the capacitors and found in the process that C10 was shorted. I got all excited for a second thinking I solved the problem, but alas, it behaved exactly the same once I fixed that.

 

[bibilit]

I will wash the board to get rid of any residue from the recap process, happened to me once also.

 

[jack]

Good idea, I will have to try that when I get back home to it (I'm visiting family for the weekend).

Do you have any advice for washing these guys? I've read elsewhere that its safe to just toss in dishwasher, but I would be scared to do that.

 

[Macdrone]

I use the dishwasher.  I will say LC's have one silkscreen that was found to be incorrect on th ecapacitor for one capacitor.  You may want to compare the caps, no matter what the replacements are.  Uniserver listed it a few years ago.  I am not sure which one it was.

 

[jack]

Well, I just finished dishwashing the board. I'm letting it dry for 24+ hours, then I'll give it a shot.

Fingers crossed.

 

[bigmessowires]

What method do you use to remove the old caps? The one and only time I did it, I used a hot air gun. It worked OK, but I accidentally unsoldered some unrelated nearby components and knocked them off the board. Fortunately I was able to solder them back in. I know you can buy double-ended soldering irons, so maybe that's a better option.

 

[jack]

I experimented a few methods with this one. On my last recap job I slowly lifted and twisted on the caps with tweezers until the legs broke; I lifted one solder pad this way .

This time, I repeated that method for the first few caps, thought it was too sketchy, then tried a few using two soldering pencils. Eventually, I tried a few where I broke the plastic under the pad, removed the plastic, and clipped & de-soldered the legs.

I don't have a hot air gun. What you were thinking of is hot tweezers; I definitely want to invest in them soon!

 

[bigmessowires]

Maybe hot air gun + kapton tape is a good enough solution, and you'd probably use it a lot more than soldering tweezers. I use my hot air gun fairly often. For desoldering surface mount chips, it's the only realistic solution. The drawback is that applying the heat isn't super precise, and other small nearby components may also get hot enough to melt their solder. Kapton tape should help.

I just did a brief search of soldering tweezers, and all the inexpensive ones seem to have poor reviews. I'm not sure a more expensive one would get used often enough to be worth it.

The hot air rework station that I have looks like this one: https://www.amazon.com/Rework-Station-Soldering-Digital-Nozzles/dp/B01M4PWU0C

 

[jack]

Thanks for the tip! I just ordered a hot air rework station... I've got three more Macs awaiting recapping right now, so I'll hold off on doing them until it comes

 

[jack]

So, I didn't break it with the dishwasher. I also didn't fix it.

Any other suggestions? I'll also poke around with a multimeter and see what I can diagnose.

 

[bigmessowires]

I would try a different PSU. I know you already measured the voltages, but maybe it has an intermittent problem, or can't deliver the fully rated amperage.

 

[jack]

No different results with the PSU from the working LC II.

Still haven't gotten around to poking around with a multimeter yet (connectivity tests, etc.). Maybe I will uncover something...

 

[Nathan]

Did you test the -5 V line? You don't mention it as far as I can tell. Maybe do a PSU recap? I would think if the drive spins up then things were okay initially. Can you boot from floppy and if so does the drive mount and is it readable?