iMac 21.5" mid 2011 CPU Upgrade and Repair

At the end of March while the school semester was still in gear, I managed to come across a particular broken iMac at Purdue Salvage. It had a broken glass screen, no hard drive, no RAM, but it was 2011 and it was only going for $100. Against some better judgement, I decided that buying it and repairing it would be kind of fun since I had never actually taken apart an Apple product and I later confirmed that upgrading components was a possibility.

I don't think you can see it very well, but there's a massive crack in the glass that spans the entirety of the screen. I didn't know this until after I took one of these apart that the glass portion of the screen is actually held on to it by some strong magnets. It was really easy to replace and (compared to buying a new iMac all together) was inexpensive to replace. It kind of makes you wonder why they decided to junk the computer.

Purdue Salvage, or the people that handed over to be tossed, decided that removing the hard drive and RAM would be a smart idea then scrapped the whole unit. So the entire process was sort of concerning because I could not confirm if there were other problems with the iMac itself, but I did the initial test of just starting it up and getting the three long(and really loud) beeps that indicated "RAM IS MISSING OR MAYBE HARDWARE IS NOT ACCEPTABLE"


Initially I wanted to install a SSD into it rather than a HDD because it was already kind of an older unit and came stock with a core i5 processor so it could use the extra speed boost. I figured since I was trying to get it up and running again I would figure out if I could drop an i7 into it while I was taking it apart.

As it happens there are a number of different sites and probably dedicated people that have determined what kinds of processors (and probably other components) that can be swapped out of certain models of Apple computer products. Turns out, theory suggested that a core i7 could replace this model of iMac. I was still kind of hesitant however, because Apple does provide an i7 2600S processor which is a low power version of the processor, but they don't mention anything about the "full" version of the i7 2600 processor. Through my power of sleuthing and the internet I was able to find posts from people that allegedly replaced their processors with the standard core i7 2600 cpu, but no one showed any screenshots of this proving one way or the other. Come on internet, provide proof of these sorts of things. How else could you be trusted?

 This was a pretty good sign. I tried using Other World Computing's HDD to SSD upgrade kit for my model of iMac. Unfortunately, I ran into some different problems. So, you can't use the Snow Leopard disk to install OSX because support for SSD wasn't available. Well that's okay, I have a Macbook Air with El Capitan and created an install USB drive with it. Try again, well, it managed to get past boot up and I was able to get to disk utility, but for some reason or another it managed to fail at the last portion of install. I still haven't determined why. I managed to get a lot of useful information and support from MacSales though. I spoke with someone named Bob Boldt with their sales team, not only is he awesome, but the entire staff that I've seen is incredibly helpful. I would strongly suggest that if you have any mac related issues/projects to check with them. They really do deserve it, credit where credit is due.



As a little side note, the first time I tried to install using the OSX disk, the drive didn't want to return it to me so I had to operate to remove it.




 Anyways, after struggling with the SSD so long, I gave up and decided that I should just use one my left over HDD that I have sitting around with some outdated version of Linux on it. It managed to install El Capitan no problem. Hooray. I wanted to install OSX first before I opened the computer up to do cpu surgery because up to this point I didn't even know if the computer was functional. Now on to the surgery.

 More useful information OWC has on their website, instructional videos (that's a direct vimeo link to the video that I found useful) that step you through installing their SSD. It is a cleverly disguised video that shows you how to install one of their SSD kits, but in reality it shows you how to take out the motherboard so that you can perform serious surgery. Apple did a good job at making everything compact and fit into it's little box, but like anything that is engineered to be compact becomes really difficult to use intuition to take apart. It's a shame they don't provide the information easily to repair their units.

There's the meat of it. Really nice, small, and a funny shaped head. The cpu is under that square bit (the heatsink) there on the right. There's a sticker that says, "warranty void if removed", but I'm not really sure what that means. I suspect it means this screw is the important one. Once you unscrew the four screws(Torx) you get access to the cpu and the rest is like replacing any other cpu in a computer.

Nice! Although, in my opinion they used probably way too much thermal paste on the original cpu, cleaning it up and replacing was pretty simple. Be sure to make sure that you have the orientation correct. I nearly put it in flipped(180 degrees rotated not flipped) until I reviewed some of my photos to double check. Always be thorough. Good advice to anyone for
anything... probably.

There see? Proof. You might have to look closely, but the top of the processor it says core i7 2600. Not 2600S, not core i5, it says i7 2600. It can be done. "But Steve that doesn't prove that it works." I hear you cry.

As I'm typing this post on my newly refurbished iMac, I can definitively say that the iMac 21.5" mid 2011 will accept the core i7 2600 processor and it is definitely not on fire.

I cut out the bit with the serial number. I am not sure if that's useful information to others, but if it is I probably don't want them to have it.

There it is. Core i7 2600 in an iMac that probably isn't supposed to have it in there. I haven't given up completely on the SSD, I'm going to be working on getting the SSD installed again and seeing if I can install OSX on it as the secondary drive. If that's successful, then I can make the HDD the secondary storage drive using the SSD for the main system. I also have been finding information about replacing the graphics card in this unit. Do I need it? Probably not, but I don't see why it wouldn't help or be a bad idea. This is now my little Frankintosh... ugh, that's a way better name than calling it Rorschach... why did I think of this now?

This was kind of fun, so if I figure out more information on a graphics card upgrade/replacement, I may make another blog post about it. I'll edit this post once I can get the SSD installed properly the way I want it to be. What did I learn from this? I learned that the cpu fan likes to be on all the time now and it is super loud, but that's okay because I have headphones for this sort of thing.

HP 3310A Disassembled and Potentiometer Repair

I originally wasn't going to make a post about fixing a potentiometer on the HP 3310A function generator because I thought it should have been relatively easy to replace/repair a simple potentiometer and wouldn't really have a lot more content to add to what I already did. Holy Packard was I so wrong. More like semi-wrong. Repairing the potentiometer was relatively easy as expected, but all the disassembling to get to it so I could even work on it was just incredible. I know in the last post I said the same thing, but friggin' kudos to HP for making a solid box of interlocking, military grade spec parts that is just an incredible pain to take apart. A majority of the photos that I took were not initially for a blog post, but rather documenting how to get this contraption back together once I realized that this was going to be a lot more extensive than unscrewing a few parts.

In the last post about the 3310A, I kind of went over a little of the first bit on how to start taking this thing apart so this is sort of going to pick up from there in the breakdown process.

The potentiometer that is used to vary the amplitude of the function generator was really erratic every time it was adjusted which suggested that the wiper contact was all gunked up with all sorts of gross just from use over time. So the initial idea here was to just replace it, but first I had get to it. Due to how the function generator was constructed, it was necessary to take it almost completely apart.

This is the side panel that screws down each of the printed circuit boards to the box itself so that it's nice and secure. Naturally, each set of screws are different sizes and have specific placements so this photo was a lot more useful to me once I had to put it back together.




But what's this? It only takes off the metal frame, but at least now we can see the board that has the potentiometer on it.

Getting the board out itself was not necessarily professional, but once the metal side frame is removed you can flex the box to wiggle out the circuit board.

Here are more photos of the board in question once it had been wiggled free. There are two other circuit boards that interface with it, one of which needs to be removed completely to get our potentiometer free.

Now that I can get a good look at the potentiometer, I figured that it might be worth a shot to see if cleaning the wiper track might solve the issue... but this only became an option after finding that the instrument room did not have potentiometers with the proper physical dimensions.

So prying back the clamps on the dust cover plate revealed this was kind of a unique potentiometer. Rather than having a single contact tooth, this potentiometer had contact teeth so to speak. The photo shows a comparison of these two kinds of potentiometer contacts.

Anyways, just from many years of use the contact teeth made tracks in the resistive strip sort of causing an eroded mess of shavings. I am not certain, but I am under the impression that the resistive strip shavings were preventing a good electrical connection. Cleaning up the tracks with ethanol worked out nicely.

Before reassembling everything, it was suggested to me by Dave Azpell that a tiny hole should be drilled in the back of the dust cover. If the potentiometer started misbehaving again ethanol could be easily applied without having to take the whole thing apart again.

 

  Here it is mostly put back together with a little video showing the output of the function generator on an oscilloscope while I adjust the amplitude with the newly cleaned potentiometer. 

EDIT (9/17/2015): Someone emailed me about getting some scans from the service manual. So here are the two sets of scans I did. I did a very basic one that included the board layouts. The second one focused on the A1 board that has the triangle amplifier and +/-5V detector.

Here's the link to my Google Drive

Repairing HP 3310A Function Generator

It is not uncommon that lab TA's report that their lab equipment is broken in some way or another. Usually it's some trivial thing like they forgot to check if it's properly powered or didn't know how to check if the fuse is blown, but from time to time the equipment is in need of some serious maintenance.

So this was brought into the back and the TA just mentioned that he couldn't get it to work. This older model function generator are usually pretty solid and don't have fuses so if they're broken then they are super broken. After some initial tests just to double check if the TA was not using it correctly, it was found that there was no output for any of the waves.

After taking the thing apart, and I would just like to give kudos to HP for their work in designing their function generator in such a way that it was a huge pain to take apart. I mean this this is a rock solid piece of equipment and my guess is they really didn't want it to be taken apart unless it really had to because it was a mystery box of sliding parts to get this jigsaw box apart. Anyways, it is pretty common for the countless detaching and reattaching of cables to the output by students just naturally wears them down and in this particular case, breaks the connection so that new leads need to be soldered. To the right, there is my handiwork with a new resistor in place. The original connector that was attached was just destroyed so I had to fashion a new connector to the board as well. This actually solved part of the problem because I was able to get the function generator to output a square wave, but the Sine and Triangle wave parts were still flat lining.

Well that was the easy task, now I had to look for something a little more malicious as to why this thing wasn't working and you can see it in this picture to the left. Some old military grade tantalum capacitors leaked and corroded away at the copper trace. On the right you can see that the trace was just eaten away.

So the service manual was found, but wasn't really necessary in this particular case because it was fairly obvious what was the culprit for the bunk outputs. I thought it was kind of interesting though and figured I would show the photo of the schematic, C2 and C3 should be the caps that I needed to replace if I remember correctly.

The only thing that needed to be done to repair this would be to fly wire the two separated traces together and drop in some new tantalum capacitors. Not too tricky.

The above photo is the new wire soldered to connect the two traces, and to the right are the new two orange caps that were soldered in.

And would you know it, everything started working again. Successful repair job to keep this HP function generator up and going for at least another year before someone drops it or something.

Big thanks to Dave Azpell for keeping the service manual and giving me guidance on what to check for to get this guy up and running again.