This space echo didn’t have anything major wrong with it, just there were a lot of small problems that made it a bit poor for performing. It is a really excellent tape delay .. partly because it has a nice muffley effect on your sound and partly because there is something quite special about the way the delay moves when you change the tape speed. It is one of those machines that feel nice to play with even though you could probably do the same with a much more compact plug-in or simulator ( Boss RE-20 .) It is quite common for people to think that it doesn’t work properly when they plug in a guitar, this is because the impedance of both the ‘mic’ and ‘instrument’ inputs are quite low so when you plug the relatively high output impedance of a guitar into it you loose a lot of the high end. To solve this you can use a guitar pedal before the input or get it modified.
Problems were just crackley pots, the spring reverb was not working and the VU back light was dead. Here is a sample of it with a Yamaha CS-10 playing through it.
A good way to repair a potentiometer especially if you do not have a suitable replacement is to open it up and clean the tracks. It really depends on the way the pot is made and whether the tracks are just dirty or are worn away. Usually … especially in older equipment , these parts are made simply with crimped metal enclosures that are easily removed and replaced by just bending its tags. I opened up the instrument volume pot then cleaned and re-lubricated it. Opening it up is shown below.
For the VU back-light I could have just found a small bulb and replaced it, but I wanted to find something a bit more long term .. an LED. Luckily the bulb has its own power supply so by using a resistor I could limit the current to get a decent glow. The main problem with using a LED instead of a bulb, is that the LED has a more focused beam instead of the bulbs diffused glow. This meant the LED had to be re-positioned underneath the PCB, rather than right next to the back of the screen of the VU.
The connections to the spring reverb were just loose and I replaced the tape and cleaned the heads. You cannot use ordinary 1/4” tape it is best to use a special paper backed tape as it is better for the heads and it lasts longer, it can be found quite easily on ebay.