Not something I have much experience with but I was recently asked to help out servicing a neglected DJ classic.
The first thing that strikes you when dismantling the deck is the solidity of the unit. The plastic is heavy, the metal is shiny everything just feels built to last.
I just needed to sort out some ancient phono leads that had become unreliable. Although this is what I did for my client, upon reflection I think I would do it differently next time. Instead of just replacing the cable I feel like adding some short inline female connectors might be preferable especially if you want to keep the mixer setup tidy and maintain flexibility.
The other task i took on was restoring the pitch control. These old sliders are about 10cm long and easy to dismantle. Inside there is a small pcb with a wiper that glides across. A ball bearing, spring loaded for dismntling excitement, helps the titch control sit in its centre position. Inside this slider it was full of food crumbs, hairs and other bits of DJ detritus. This was mixed into a soup or more of a paste due to excessive cleaning activity.
Many people casually spray chemicals into their equipment hoping to wipe away years of wear but actually this is just doing damage. Most potentiometers or sliders are lubricated with a jelly like paste called silicone grease on the moving parts. This paste is not on the carbon track but the issue is that when cleaning if you use too much switch cleaner then it just dilutes the grease and causes a messy pot that doesn’t move smoothly.
How much is too much? Well I would say a tiny squirt which lasts the same amount of time as when you click your tongue. A real blip. Once applied you can move the pot end to end ten or twenty times. Exercising the pot distribute the cleaner and hopefully remove oxidisation but leaves the lubricant where it should be, that is on the moving metal parts. I suspect that many people think more cleaning chemicals is better but this is definitely not the case.
So think carefully before you spray.
Calibrating the speed control is performed in two stages. First measure the slider resistance and ensure that it is 2700 ohms between red and brown with slider disconnected from the main PCB. Next ensure that the frequency is as per the tech spec by measuring on the test point on the main board using a good frequency counting meter.