DIY Fixer upper

[Lucas]

I've got a Lexicon MPX500 that is seriously noisy (hiss), that I didn't spend much on. I'd like it fixed but the service cost will be more that I what I paid for the unit itself.

My knowledge and experience with electronics is limited to lead maintenance (well maybe a little more than that, but not much more...)

If I decided to have a crack at tracking down the problem myself, what would I need beyond a soldering iron and and multi-meter? I'm guessing the cost of the required measurement equipment might make this unviable?

[Ben M]

Hey there Lucas. There are so many variables with what the issue could be. Could be caps, could be blah blah... power supply or on the main board etc.....
If you have limited experience with this stuff I'd keep your probes out of there with 240v on. Even give it 10 mins after powering off before probing around. Some components hold a charge for a few mins while the power fades.

One thing you could do that doesn't require probing (or life threatening activity) is - flip the lid and have a look at the condition of all the capacitors. If some look a bit bulky and bloated then they may need replacing. Another thing is you could reseat any IC's that are in the unit. All with 240v off.

I'm guessing the cost of the required measurement equipment might make this unviable?

The cost of getting spiked with 240 would definitely make this unviable.

cheers

[Lucas]

Great, a good place to start. Cheers!

[Alistair]

+1 on what Ben said, as well as a meter and iron, the most important thing is patience. It could be something simple, but in a unit like that there could be hundreds of things that could have gone wrong. Good luck!

And whilst it may or may not be applicable with this unit, I'd suggest you do some internet searches on the dangerous bits of electronics. Learn where 240v is likely to be present in a circuit, which parts may store high voltages even when turned off (and how to discharge them- eg draining caps), how to check that the grounding is actually safe in a unit. It may not be as exciting, but it's definitely worth knowing before you stick your head in there.

[rob]

no high voltages will be "stored" in the unit after power off.
Does it pass audio? Do all the functions work? Does the gain structure of the unit seem correct?
What sort of noise? hiss or crackle or buzz?
If the unit doesn't seem to losing level and thus you aren't cranking up huge amount of gain after the unit, thus creating a hiss noise, then it will get tricky finding the noisy part. If it is losing level passing through the unit and this hiss is from all the gain you are applying after the unit to recover your signal then you probably have a bad coupling capacitor.

[Lucas]

The noise is hiss. Hardcore hiss.

The unit passes audio, is fully functioning and all gain stages are operating in the correct manner. Gain structure is set correctly.

That said...

I'll double check all of that tomorrow.