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sixsevenco

Need guidance on Classic II repair

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Hi Everyone,

 

My Classic II arrived!  Cosmetically, it's beautiful, but it definitely needs recapping.  The electrolyte fluid leak is very obvious.  I don't see any corrosion, so that's good.

 

Anyway, I have tried to do my homework, and figure as much of this out as possible.  But I've hit a point where I am stuck, and I could use some help.  My board has 13 capacitors.  Looking at the reference for my board at maccaps.com, I see that I need to buy the following replacements capacitors:

 

8 - 10µf - 16V - SMT
3 - 47µf - 16V - SMT
2 - 1µf - 50V -SMT

 

First Question:  For the first capacitor (10µf - 16V - SMT), there are 887 options on Digikey that meet these specs.  How do I narrow this down to a specific capacitor to buy?  Do I need to worry about tolerance? Dimensions?  Or should I just go with the lowest price?

 

Second Question:  Should I recap the power supply while I'm at it?  The caps on the power supply seems to be through hole, so that will likely be an easy task...

 

Third Question: I've read that there is a bleeder that should discharge the CRT.  Any chance that isn't working as intended?  I've never worked with CRTs before, so I'm a little intimidated. 

 

Fourth Questions: Are there any guides on how to service/lubricate the floppy drive?  I haven't found any.  (admittedly, I haven't looked that hard.)

 

Thanks

 

67

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2# You definetly should. Classic/Classic II analog boards are prone to break down due to leaky caps.

 

3# It can fail. Regardless of that I always do a manual discharge if I have to remove the anode cap. I never had it fail yet but better be safe.

As long as the work I am doing in there does not involve taking the anode cap off there is no need for discharging if you ask me.

Edited by Bolle

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13 hours ago, sixsevenco said:

First Question:  For the first capacitor (10µf - 16V - SMT), there are 887 options on Digikey that meet these specs.  How do I narrow this down to a specific capacitor to buy?  Do I need to worry about tolerance? Dimensions?  Or should I just go with the lowest price?

 

67

Start by filtering "active". Then "tolerance". %20 is generally acceptable for these systems. Then try to determine the dimensions of the component you want to replace.

Also if you can read the PN on the existing component you can usually google up a reference.

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Thank you to everyone that has responded so far.  I'm off to the races!  (Well, I'm actually not racing.)

 

I removed all the caps, and next step is to clean the board.  That being said, I have a problem.  I was a careful as I could be, but I ended up lifting a pad for capacitor C12. I need some guidance on how to work around this.  According to the wiki, I can use a wire to work around this, but I'm not sure how.  Any help is greatly appreciated!!!

 

Quote

What happens if you DO lift a pad? We've all done it lots of times. It happens. Don't panic. Often times it's as simple as applying a tiny amount of super glue underneath to reattach the pad. But if the pad has completely come off and is no longer electrically attached, follow the trace on the circuit board that it used to be connected to, until you find a place where you can solder a small wire. Do so, then cut the wire to length and solder the other end to your new cap.

 

IMG_0822.JPG

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So, I'm trying to figure this out.  I think I am making progress, but I would love for someone to confirm if I am approaching this correctly.

 

It appears to me that missing the C12 pad trace leads to C52 on the other side of the board.  I've tested for continuity with my multimeter.  As a solution to the missing pad, I think I need to solder a wire to the negative terminal on the replacement C12 capacitor, and wrap it around the board and attach to C52 in my picture below. Is that correct?  Is there a diagram somewhere that could verify this?

 

Any responses are appreciated.  Even if I don't get a response, I'm also trying to document my problem, and hopefully the solution to help others in the future.

C12.png

C52.png

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16 minutes ago, Bolle said:

Solder some really fine wire to one of the two vias instead. No need to wrap a wire around the whole board.

 

Thank you!  Are the vias conductive? That was my first thought as well. I tried them with my multimeter probes and got no response. I assumed they had some sort of coating on them...

 

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If there is coating on there carefully scrub it away. If your wire is fine enough to go inside the via you should get away without removing any of the protective layer. Your probe probably did not reach far enough into the via to make contact with the tiny copper inlet.

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