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Teraforce88

LC II Restoration project

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Greetings,

 

With the coronavirus pandemic going on and my governor giving a shelter-in-place order as a result, I've been furloughed from my job, which has given me time to finally begin restoring my Macintosh LC II that my family bought new in 1993.   About 5 years ago, I posted a video on YouTube showing a problem that it had regarding the video output:

<iframe width="560" height="315" src="https://www.youtube.com/embed/vtpZmFiManc" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

 

Three years later, the power supply died.  It kept making a faint ticking sound, which corresponded to a faint clicking from the speaker.

 

A few days ago, I re-capped the power supply.  The LC II works again, but the flickering jailbars are still present.  They behave *slightly* differently, though.  It seems that their flickering can be affected by both hard drive activity and floppy drive activity, which I didn't notice before.  I do see some electrolyte on the motherboard, so I still need to re-cap the motherboard, but I'm wondering if I'm still having some PSU issues?  I ask because:

1.  The fact that the flickering jailbars can be affected by the floppy drive and/or hard drive

2.  When I measured the voltages from the power supply with it disconnected from the motherboard, the +5 and +12 lines looked good, but the -5 was jumping between -3 and -3.8 volts.  During this time, it was making the same ticking sound that it made when it died, but when I plugged it in the LC II's motherboard, it seemed to work fine (I haven't measured the voltages from the PSU while it's plugged into the motherboard)

3.  Over the last few days, I've had my LC II powered on for about 6 hours.  The hard drive has been running perfectly fine while opening various programs, files, and folders except for one time, where the hard drive slowed down for a second when I opened up a folder, then sped back up.  The LC II froze during that second, but then carried on.
 

My next plan of action is to re-cap the motherboard, but I would like to know if there actually is something wrong with the -5V line on the power supply, or if I just need to measure it while it's plugged into my LC II.

 

Everything else works fine on the LC II except for the microphone jack, which appears to be dead now.  

 

Thanks,

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Recap the motherboard. The -5 volts isn't as necessary as it seems - my LC II is only given +5 and +12 volts, and I can print to an ImageWriter II, and sound works fine. -5 volts might be necessary for some serial stuff, depending on what it's connected to, but it wouldn't be the cause the issues you're having.

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6 minutes ago, johnklos said:

I can print to an ImageWriter II, and sound works fine

Oh, interesting.  My understanding must be wrong.  Maybe it's used for the differential signalling on the serial line and the ImageWriter doesn't need that?  Rampant speculation on my part.

 

Anyway, yeah, @Teraforce88, it isn't the -5v line :-)

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Thanks for advice, everyone!  I apologize for not posting for a while.   I pulled off the Apple //e emulator card to reveal the caps, and boy oh boy is there some corrosion or what (see attached pic).  There's even a trace or two on the board that appears to be darkened because of the corrosion.  I remember trying to clean the corrosion off several years ago with Q-tips and rubbing alcohol, but that didn't seem to make much of a difference. 

 

I'm going to go ahead and order some capacitors off of Digi-Key, but I still have a few questions:

1.  Since these are surface-mounted capacitors, what's the best way to remove them?  I think the safest way is to use two soldering irons, which I don't have.  PotatoFi mentioned the "Twist and Push" method when he was removing the caps from his LC II; can someone elaborate on how this is done?  Or should I go ahead and just buy a 2nd soldering iron?  I just don't want to rip any solder pads. 

 

2.  What's the best way to clean the corrosion off the motherboard, particularly under the various ICs? 

 

3.  PotatoFi replaced his electrolytics with tantalum capacitors.  Aside from appearance, is there any advantage to sticking with Electrolytics as opposed to converting to tantalum?

AHS_1370.jpg

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1 hour ago, Teraforce88 said:

PotatoFi mentioned the "Twist and Push" method when he was removing the caps from his LC II; can someone elaborate on how this is done?  Or should I go ahead and just buy a 2nd soldering iron?  I just don't want to rip any solder pads.

"Twist and Push" method is just grabbing the capacitor can with a pair of needle-nose pliers, pushing down, and twisting it a little bit back and forth until the leads inside the can fatigue and break. If the plastic base of the cap is left behind, remove it with tweezers. You'll also have to desolder what remains of the leads from the board.

 

The "two soldering irons" method isn't the worst, but it's definitely not the safest either. Bear in mind that excessive heat can lift pads very easily.

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8 hours ago, Teraforce88 said:

Aside from appearance, is there any advantage to sticking with Electrolytics as opposed to converting to tantalum?

 

It's perhaps the thing of holy wars, or simple personal preference, but here's some advantages I can see:

 

- Circuits were likely designed with electrolytics in mind. Tantalums have some different properties. 

- Electrolytics tend to fail open, not short, as proven by time and history. Cap goo is bad, but a short may be extremely bad. Unclear if tantalums are more likely to fail short. 

- Tantalums feel a bit more 'uncertain' in the longrun. 

- You can get the exact pad fit of the factory caps with electrolytics. 

 

The electrolytics in these old machines were relatively new technology at the time. Modern caps, especially more-expensive long-life ones, should last a whole lot longer. I landed on the Nichicon UCB ("Long Life Assurance") and UCW ("Low Impedance, Long Life Assurance") lines for the recaps I am currently diving into. 

 

This all said, there are people who have been doing this much longer than me who choose to use tantalums. 

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On 5/20/2020 at 6:12 PM, AwkwardPotato said:

"Twist and Push" method is just grabbing the capacitor can with a pair of needle-nose pliers, pushing down, and twisting it a little bit back and forth until the leads inside the can fatigue and break. If the plastic base of the cap is left behind, remove it with tweezers. You'll also have to desolder what remains of the leads from the board.

 

The "two soldering irons" method isn't the worst, but it's definitely not the safest either. Bear in mind that excessive heat can lift pads very easily.

Interesting!  I had no idea that excessive heat could lift the pads.  I did see a video where someone used a hot air gun to desolder the capacitors on a Mac Classic II, and it seemed to work well for him:

https://www.youtube.com/watch?v=SjgWo7mj8-w

 

I also saw this video, where you apply solder to each pad, then heat the pads up to lift the caps, but I'm afraid that would lift the pads. 

https://www.youtube.com/watch?v=mMMT1qLMX28

 

How do you guys feel about these methods?  Or should I just stick with "Twist and push"?

Edited by Teraforce88

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If you actually have a hot air rework station, the risk you run using it over dual soldering irons is considerably lower. Emphasis on the "rework station" part; the kind of heat gun you find at the hardware store isn't really optimal for this kind of work. Heating and lifting each side of the cap as shown in the second video is very likely to lift the pads on a board as corroded as yours.

 

Also, to answer your question about cleaning the board: my personal preference is to fill a plastic tub with tap water and dish soap, put the board in, gently scrub with a toothbrush, and rinse the board with distilled/deionized water.

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Reading this entire thread is what sold me on push & twist:

 

Try to find some junk boards with similar SMD caps to practice the whole process on, including cleaning the pads and soldering on the new ones. I was able to find some in an old cable modem and dead HDD controller in my junk bin. 

Edited by dzog

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Following up slightly on the electrolytic vs tantalum debate as I was researching around a bit more ahead of another DigiKey order for my own recap projects. 

 

It's funny. In Mac-land folks often want to replace their electrolytics with tantalums as they want to avoid dealing with cap goo again. In other vintage restoration communities, I've seen the opposite: folks wanting to replace tantalums with electrolytics so that they never have to deal with an explosion or short again. 

 

e.g. 

https://www.vogons.org/viewtopic.php?t=57466

https://forums.qrz.com/index.php?threads/tantalum-cap-life-expectancy.331027/

https://audiokarma.org/forums/index.php?threads/replacing-tantalum-caps-with-electrolytic.869045/

https://electronics.stackexchange.com/questions/99320/are-tantalum-capacitors-safe-for-use-in-new-designs (focused on pros vs cons new designs, some interesting write-ups)

 

 

Edited by dzog

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As far as use within electronics goes:

Electrolytics usually have higher voltage and Farad capacity than other types but they're generally fairly large and typically polarized. Tantalums have fairly high voltage and Farad capacity and are also typically polarized but are generally smaller than other caps with the same Farad/voltage values, plus they're solid so they often handle heat or vibration better than electrolytics. Various film and ceramic types usually have low Farad capacity but very high voltage capability, and they're typically unpolarized so they're usable in applications where AC is present, often employed as filter or bypass caps in power supply circuits.

The different types will have different characteristics of course, so it's generally a good idea to replace like-for-like, especially in a tuned circuit like a TV or radio equipment. In simple power supply/filter duty on a computer board, though, it generally doesn't matter what type you use so long as the values are the same (polarized or not, Farad rating, voltage rating, temp rating) and there's not too much of a size difference.

 

Really the big concern with electrolytic vs. tantalum properties is mostly when used in A/V equipment or potentially in applications where a short-type failure will cause severe problems. The audio restoration people obviously carefully match their capacitors because using the wrong type or value will adversely affect the sound they get out of their equipment, and someone who pays over $1000 for a cassette deck (not including the several thousand more for the amp and speakers and OFC cable to wire it all up) will want the best they can get out of their device. However if you're playing SimCity or The Playroom on an LC II, you're not going to notice a difference in sound quality with electrolytics vs. tantalum. 

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5 minutes ago, Franklinstein said:

However if you're playing SimCity or The Playroom on an LC II, you're not going to notice a difference in sound quality with electrolytics vs. tantalum.

Funny - I posted a serious question on Reddit about the best small case speaker precisely for my restored & recapped LC II.

 

I used tantalums with a plastic diaphragm speaker (which can be seen here), and the audio sounds wonderful. Granted, though, I have no idea how the same speaker would've sounded before the recap.

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A good speaker also makes a difference. Generally as long as you keep impedance the same and wattage the same or higher, you can use pretty much anything that fits. The audio circuit in the LC II isn't amazing by any stretch even with a great speaker, though, what with its 22k sample rate and mono sound. It's better than the average beeping PC from 1992, of course, but can't hold a candle to a good SoundBlaster or newer/higher-end Macs. But again, you won't really notice the limitations with SimCity or The Playroom or any other program you're likely to run on there.

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I've wondered about the whole electrolytic vs. tantalum thing myself. So far, I've recapped:

  • 2x LCII
  • 2x SE/30
  • 2x Classic II
  • 2x Performa 476/Quadra 605

All tantalum caps. Zero problems so far.

 

In regards to desoldering vs. "twist and push", I was a die-hard proponent of "desolder, rock to the other side, desolder" until I lifted two pads on my SE/30 in a row. Someone on the forum suggested twist and push, and given the current heartache on my SE/30 I decided to give it a go. I've done 4 boards since then, and lifted (not destroyed) only one pad. If you read back on my posts a bit you'll find older ones where I mock "twist and push", but that is what I do 100 percent now.

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I've removed all the caps from over 20 IIcx boards without lifting any pads using the two soldering pencil  method.  

 

I think it has a lot  to do with what one is comfortable with.

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