Last year I purchased an M-Audio Axiom Pro 49 keyboard from eBay. Although I had several 'keyboards' already, I didn't have a 'normal' midi keyboard, which I hoped this would work as.
The keyboard was described (on eBay, where I purchased it from) as being in good condition, but with two broken sliders. However, when I received it, the case was actually quite different (as unfortunately often happens with things bought from eBay). The USB port was very loose and to get the keyboard to work with my PC I had to hold the USB cable in at a certain angle, and stick something heavy on the cable to keep it in place. Some of the keys also make quite a 'croaky' noise when pressed, but they do seem to work okay.
Opening up the keyboard wasn't too difficult, but there are a lot of screws to undo. You don't need to undo the large black screws in the middle of the keyboard's underside, just all the other screws. With the screws undone you can remove the top of the keyboard.
After that you need to remove a few screws holding down a long metal bar that goes across the top of the keyboard. Then you can unscrew the board with the sliders, undo the ribbon cable that attaches it to the main board, and remove the slider board.
I unsoldered one of the broken sliders and found it was an Alpha branded B10K 45mm (30mm travel) slider pot. However, I couldn't find the exact same model anywhere. The nearest I could find is the RA3043F-20-10EB1-B14, which looks to have a plastic rather than metal lever. This is also available on Amazon: Taiwan Alpha Electronics RA3043F-2010EB1-B10K 10k8486; 1/5W PC Mount Linear Taper Slide (Pack of 3).
Although there are plenty of cheap 45mm length (30mm travel) B10K sliders on Ali Express, they all seemed to have the contact pins on the outside of the slider, and also be missing the two inner PCB mounting pins. The Alpha sliders used on the Axiom board have their contact pins a bit further in from the ends of the slider. The only suitable ones I could find on Ali Express were ALPS branded ones, e.g. RS30 Series ALPS Switch 45mm 4.5cm Mono B10K Slide Potentiometer Speaker Mixer Faders Shank Length 10MM, you can find more at the top of this page of search results, and the end of page of the same search results (at the time of writing): 45mm B10K search results page 3.
From eBay I managed to find a set of 4 unbranded ones that look correct: B10K Slide Potentiometer 30mm travel single unit 45mm Length short shaft x4pcs. These were $15 + $2 P&P, and what I purchased. The ALPS ones from Ali Express were $4.5 + $3 P&P ea. The Alpha ones from Amazon were $10.81 + $4.17 P&P. The Alpha ones from Mouser UK were only about £1.5 each, but they didn't have any in stock, and I suspect P&P would probably add quite a bit to the cost as well. The ideal purchase would have been this ebay listing for Alpha 45mm B10K 10K Linear Taper Slide Potentiometer, as that looks to be exactly the same model as is used on the Axiom slider board. However, they only had 2 in stock (which is the number I needed, but I preferred to buy from a source where I could order more in the future should the need arise). They are also much more expensive at $7 + $3 P&P each.
Getting the main board out to look at the USB port was a right pain, it's extremely annoying that the ebay seller didn't mention the broken USB. I only paid £15 for the keyboard though, so I didn't think it was worth sending back for a refund. To get the main board out you have to remove all the various ribbon cables that go into it, and they were very tight and difficult to remove. On one a wire end popped out of the connector as well (no, I wasn't tugging on the wires to pull out the connector blocks).
With all the connectors removed (and the board unscrewed) I could check the USB connection and see that the part with the contacts actually moved quite a fair way back when you pushed it. The female USB B connector block has 4 pins centred on the bottom, so I bought a pack of 10 of these of eBay for £2. I also bought a pack of 10 new slider knobs, since I will need to replace all the slider knobs to keep them matched. So the cost of the sliders, slider caps, and USB connector is actually more than the actual keyboard cost (though less when you include the postage cost on the keyboard).
When trying to find the replacement sliders needed for the keyboard, I found a video about repairing the Axiom 61 keyboard. That said that the individual sliders weren't available, and you have to purchase a complete slider replacement board from M-Audio. They said the cost was only $20, which works out much cheaper than buying the separate sliders anyway. However, it seems you can no longer purchase this board, and the places online that have it listed (but out of stock) charge around $60 + P&P and that price would also attract 20% VAT and £10 post office fee to import into the UK if it was in stock for purchase.
After receiving the sliders and USB connectors I replaced these okay. But the keyboard required the separate power adapter to be plugged in for it to work, when it is meant to be able to take power over USB. Investigating this I found that a component had been ripped off the board behind the USB connector. And I had no idea what type of component this was.
M-Audio's support was completely useless, telling me that I needed to get a replacement main board, which are no longer available. Thankfully I managed to get some help over at electronics stack exchange, where the missing component was identified as probably a ferrite bead. So bought several different values of those (not knowing which value was needed), making this keyboard even more expensive.
When looking to purchase the ferrite beads, I was first looking at Ali Express, but they were quite expensive. I then looked on Mouser, where you could purchase them individually very cheap. But postage was very expensive. Finally I remembered RS Components, a UK based company. Some of the beads on there were only available in very large quantities, but most were available as packs of 10 - 25. While I was looking I also noticed they had the correct slider for the keyboard, and at a decent price (I think this one: Alps Alpine 1 Gang Slide Potentiometer, ±20%, 0.2W Power Rating, Linear, Through Hole ).
So after disassembling and reassembling the keyboard many times, a large amount of time spent looking for the correct parts to fit (and quite a bit of time fitting them) I now have a working keyboard. The only thing I'm still waiting for is the caps for the sliders, which I think must be lost in the post. So I might have to buy those again.
