Although not the cheapest, ebay is probably the easiest way to find faulty systems.

Some equipment recommendations:

• A TS100 soldering iron. I use a more expensive Hakko FX888-D, but I've heard great things about this one for the price. Try to get a chisel tip for general purpose use, it has a balanced combination of size and heat transfer.
  
• iFixit 64-bit toolkit, for handling all the various screws you'll encounter.
  
• Soldapullt desoldering pump. Don't bother with the Chinese knock-offs, they seem to break easily.
  
• Fine 63/37 solder. One roll will last you a long time. Don't bother with cheap Chinese solder, it will not have the advertised metal composition and give poor results.
  
• I like this flux, but it's kind of pricey.
  
• Desoldering braid is essential.
  
• Neoteck multimeter. Very good for the price.
  
• If you need to remove SMD components, a 858D hot air station available under various Chinese brands you've never heard of. Kind of sketchy, but works and has not burned down my home yet.

To mention some other homebrewing supplies and tools that haven't come up here:

• Copper Clad PCB Board for Manhattan or Dead Bug or Island Pad circuit construction.
  
• Perf Board for circuits involving many IC's or other 0.1"-spaced leads.
  
• A Solder Sucker, for clearing solder from perf-board
  
• Solder Wick, for removing solder from things that aren't plated holes.
  
• A cheapie Rotary Tool, for making isolation pads, cutting boards, rounding off edges.
  
• A decent multimeter - decent used to mean something in that $30-$50 range, but now even down in the sub-$20 range you're looking at plus/minus 0.5% accuracy for voltage measurements, which is good enough for most homebrew purposes. Whatever you do, get one with a continuity alarm! A $6 meter without one is a $6 waste of your money.
  
• A decent Soldering Iron. I spent years thinking I was bad at soldering, turns out I was bad at buying soldering irons. A 15W radioshack fixed iron with a fat tip will do you no good. The 50W adjustable pencil linked here it solid, though many people (myself included) prefer a soldering station
  
• A pair of fine need nose pliers and a flush cutter. Xuron is the name brand, but excelite or hakko or most others are fine.
  
  

Build Log 5: Viterbi

Highlights

• Viterbi split ortholinear 70 key keyboard from keeb.io
  
• Kailh Pro Purple Switches from NovelKeys
  
• DSA Honeywell Keycaps from PrimeKB
  
• Socketed Pro Micro controllers
  
• First personalized QMK keymap!
  
  

  Parts List
  

• 1x Viterbi PCB Kit
  
  • 2x Viterbi PCBs (Rev 1.0)
    
  • 2x Push buttons for reset
    
  • 2x 4.7kΩ resistors
    
  • 2x TRRS jacks
    
  • 78 1N4148 diodes
    
• 70x Kailh Pro Purple Switches (Tactile 50g)
  
• 1x Black PCB Viterbi Plate
  
  • 2x PCB swtich plates
    
  • 2x PCB bottom plates
    
  • 16x M2 6mm screws
    
  • 8x M2 11mm standoffs
    
  • 8x adhesive bumper pads
    
• 1x Silver Sheathed TRRS Cable
  
• 1x DSA Honeywell Keycaps
  
• 1x Red Rubber O-Rings
  
• 2x Pro Micro (ATmega32U4)
  
• 4x Mill-Max 12 Position Ultra Low Profile Socket
  
  

  Resources
  

• Nyquist Build Log
  
• An Overly Verbose Guide to Building a Let's Split Keyboard
  
• Socketing a Pro Micro
  
• A Guide to Flashing a Let's Split for Beginners (Windows)
  
• Build Log 1: Nyquist
  
  

  Tools
  

• Hakko FX888D-23BY & Flush Cutters
  
• Hakko T18D16P Tip for general purpose soldering
  
  • The tip that comes with the FX888D is either this tip or one that is extremely similar.
    
• Kester Rosin Core Solder (63/37 .020)
  
• XOOL ESD Tweezers Tools Kit
  
  • ESD-15 for most work, especially inserting the wires during controller socketing
    
  • ESD-34A for desocketing the Pro Micro controllers after they've been socketed (as a pry bar under the controller and then as a wedge between the underside of the controller and the top of sockets)
    
• Engineer SS-02 Solder Sucker
  
• NTE Electronics SW02-10 Solder Wick
  
  

  Notes
  

• The Viterbi build process is pretty much the same as the Nyquist, with the addition of 10 keys. The other difference is the placement of the two resistors, which now are only installed on the master side (the side with the USB cable, the left hand side).
  
• When flashing, I wasn't able to find eeprom files specifically for the Viterbi. I instead used the eeprom files from the Nyquist and everything seems to be working so far.
  
• Some of the keys are a bit crooked... I'm not sure if this is the switches themselves, or me somehow soldering the switches crooked.
  

Here’s the solder wick I got that works great! https://www.amazon.com/dp/B0195UVWJ8/ref=cm_sw_r_cp_api_i_z1kcBbWDJCB0T

LOL, that last part, it's happened to all of us though being honest. :P Anyways u/superuser41's suggestions are spot on. I use a Hakko FX888D myself & love it, very nice station for the money IMHO. Never used that particular sodapult but they are well regarded in the community.

Edit: This is a good tip for soldering switches & LEDs (my personal fav size/type for it). You may want to grab a few, it looks like the linked bundle only comes with one tip. Also this is a high quality solder in the right diameter for soldering switches/LEDs. This is good solder wick, This is a good flux, & I always recommend getting some tip tinner.

60/40 rosin core should be good.

Alpha Fry AT-31604 60-40 Rosin Core Solder (4 Ounces) https://www.amazon.com/dp/B00030AP48/ref=cm_sw_r_cp_apa_BhXXzbASH0FHM

Use solder wick and a wide tip to clean the old solder off

NTE Electronics SW02-10 No-Clean Solder Wick, #4 Blue, .098" Width, 10' Length https://www.amazon.com/dp/B0195UVWJ8/ref=cm_sw_r_cp_apa_9eXXzb1S3RHKS

Use lots flux. Coat the area before you use the wick and again before you solder. It helps bond the solder to the metal.

MG Chemicals No Clean Flux Paste, 10 ml Syringe https://www.amazon.com/dp/B00425FUW2/ref=cm_sw_r_cp_apa_mgXXzbTRM5G78

A good iron helps so very much. This is what I have

Weller WES51 Analog Soldering Station https://www.amazon.com/dp/B000BRC2XU/ref=cm_sw_r_cp_apa_RiXXzb76H6WDS

However this should do for occasional use

Vastar 60W 110V Welding Soldering Iron with Adjustable Temperature Dial, 5pcs Interchangeable Different Soldering Iron Tips and Solder Tube for Soldering Repaired Usage, Blue https://www.amazon.com/dp/B071RCB7KB/ref=cm_sw_r_cp_apa_slXXzbQRJVVZ2

When you are done clean with 90% or above isopropyl alcohol and let dry before you use.

Watch some videos on how to use the wick. Its a great tool to have and works so much better than the crappy suckers.

https://www.amazon.com/NTE-Electronics-SW02-10-No-Clean-Solder/dp/B0195UVWJ8/ref=sr_1_2?ie=UTF8&qid=1498946921&sr=8-2&keywords=copper+wick

As was said before, these are rotary encoders.

I had an old piece of gear with these. One knob was broken. I discovered there are many options to consider for what the encoder is:

• switch or no switch - these look like the kind that do not have a push switch
  
• detent or no detent - if the shaft makes clicky feeling feedback when you turn it. I am guessing these don't because they are the tone stack knobs.
  
• The number of pulses per revolution. This is not possible to tell by looking at it. or from detents. But usually these are 24. There are other kinds too
  
• The orientation - vertical or 90 degree. these look like vertical right.
  
• the pin type - surface mount or pc pin. hese look like pc pin.
  
• panel mount or pcb mount. These look like panel mount because the threaded screw around the shaft
  
• encoder tech (mechanical or optical) - these are mechanical
  
• the output type (quadrature, binary) - because the 3 pins, these are quadrature
  
• the shaft length - if the shaft is plastic or metal is not as important. these look like 20mm
  
• the shaft pattern (straight, fluted, or slotted) - these look like slotted.
  
  So probably this https://www.digikey.ca/product-detail/en/bourns-inc/PEC11R-4020F-N0024/PEC11R-4020F-N0024-ND/4699190
  
  ​
  
  In general, I used their search filters, here is a link to one less narrowed down too https://www.digikey.ca/products/en/sensors-transducers/encoders/507?k=&pkeyword=&sv=0&pv545=142&sf=0&FV=fffc0076%2Ca4019a%2C1140291%2C6240002%2Cffe001fb%2C3400006&quantity=&ColumnSort=0&page=1&pageSize=25
  
  ​
  
  To remove these from the PCB, you need to be good at desoldering. I used a solder iron with desolder wick
  
  ​
  
  I have this solder station https://www.circuitspecialists.com/csi-premier-75w-Soldering-Station.html
  
  A good solder station is important as the tip is very fine point, the heat is regulated and can be adjusted. I used about 350 to 400 degrees C heat. And the device is safe to use for static sensitive boards.
  
  And solder wick https://www.amazon.ca/NTE-Electronics-SW02-10-No-Clean-Blue-098/dp/B0195UVWJ8/ref=sr_1_1?keywords=solder+wick&qid=1565443539&s=gateway&sr=8-1
  
  Having some fine tweezers is good too. I have these https://www.amazon.ca/TWEEZERMAN-Stainless-Tweezer-Assorted-Colors/dp/B000782SQY/ref=sr_1_54?keywords=tweezers&qid=1565443795&s=gateway&sr=8-54
  
  ​
  
  It is very important to not damage the circuit board when desoldering. be patient. The hard part with taking out rotary encoders is desoldering the mechanical support metal clips on the sides. These usually are wider and require more heat and time to melt and more messing with the solder wick to get all the solder out. I recommend desoldering the pins first, using small tweezers to move the pins to make sure they are loose. then work with the iron to alternate the mecanical support pieces to heat and gently rock back and forth.
  
  ​
  
  Another thing migh to try is to destroy the old broken encoder, small cutters to cut apart the pins and the supports. Just be careful again to not damage the other parts and the board. Then you can easier desolder the loose bits of metal remaining in the holes.
  
  The approach worked well for me. I had a few iterations, since the first time I replaced an encoder, put the device back together, then i found a different encoder had stopped working. So back apart and I had to desolder it as well. But then I went on the learning curve of getting an encoder with the wrong number of pulses per revolution. It was a big wheel for the options, so it had 24 detents, but 12 pulses per revolution, and a push button switch, so some kind of special snow flake.
  
  If these encoders you have here are just regular encoders without switches it should be possible for it to be repaired.
  
  Of course if you don't have the tools already then it can be very expensive to ge them just to do this. I would recommend then finding someone who does have the tools and experience doing this.

The wires have to be disconnected, otherwise you will be measuring the parallel resistance of the speaker and the crossover board, which is different than just the speaker alone. Since parallel resistance is always less than the lowest of the separate resistances, that means the board could read 8 and your speaker could read 50 and your meter would say 6.9 measuring them together.

The sticker on the side says it's a 6 ohm, so it should measure somewhat close to that. If you get some solder wick and a solder sucker, de-soldering becomes much easier.

The backs of those tweeters do look different. Is that black part on the back the magnet, or is it a plastic cover? It makes me think maybe someone has been in these speakers before trying to figure out what was wrong with them. Although, it could be that they're just a different year and design than the other ones. Testing them will at least give you a rough idea if the voice coils are shot. You could replace them but if that doesn't fix the problem, then you've spent a lot of money for nothing. I prefer to test things and only replace the broken parts.

If you're convinced there is something wrong with these speakers, and you can't find anything wrong with the tweeters, then I think you may have no choice but to dig into the crossover board. It's the most likely culprit. The nice thing is, caps are not all that expensive, they're just a lot of work.

On the high end stuff, sometimes the crossover is integrated with the wire hookups, so you unscrew that from the back and pull it out. But if these don't have anything like that, you might have to take out the woofer. Make sure you save all the stuffing and put it back when you're done. Either way, there should be a way to access the board, usually either through the back or the woofer hole if the cabinet is glued together.

Still, make sure you double check everything upstream before you tear these speakers apart. This really sounds like an amp or a source problem.

This is what I got and it works pretty well. Try adding a little more solder so the wick can get better access to what's left and take it all away.

https://smile.amazon.com/NTE-Electronics-SW02-10-No-Clean-Solder/dp/B0195UVWJ8/ref=sr_1_4?s=hi&ie=UTF8&qid=1498369574&sr=1-4&keywords=solder+wick

additional parts
ribbon cable
Pro micro 3 pack
solder
Flux
Solder Wick
EDIT
In case you lose your marbles