Electronics 2000

Hi. I'm a bit of a newb. I studied electronics in high school but there's a lot of details i don't remember.

I'm trying to fix a synthesizer (Korg 01/W Pro x). There is no screen display and no sound however all the MIDI functions work. A couple times after leaving the synth on for a while, it would all come to life with sound and display all at once for about 15 mins or so and then go away again. so I'm going through and checking for bad resistors and capacitors, however I don't know how to test a capacitor, and I need to be able to test it while in the circuit. I can't take all the capacitors out and test them.

Any thoughts?

Thanks!

It's a bit tricky testing any component 'in circuit', not just capacitors. You need to have an idea of the surrounding circuit so you can decide what to expect when you apply your test. Which leads into another point, if you're using a multimeter to probe either side of the component you need to understand how the multimeter is interacting with the circuit...

In your circumstance I would at the very least start with my multimeter in VDC mode, start at the low voltage side of the power inlet and check correct voltages are present both when the device is working properly and especially when it's in failure mode. Work downstream into the system. You may well need an oscilloscope if your DVM doesn't reveal anything. However, don't do any of this if there's mains voltage going into the system and you have any doubt about which bits are high voltage!!!

Electrolytic capacitors have a habit of failing over time, check for domed heads, or if they are raised from the PCB surface have a look between their legs to see if the sealing cap has pushed out - sure sign of a failed cap. Cable interconnects are also a weakness, make sure they're all pushed home fully. If there's a processor in the system anywhere check for a clock signal. That's enough to think about for now...

William
http://www.labtronix.co.uk

That sounds (pun) like a thermal intermittent in the power supply section which could be caused by an electrolytic capacitor or something else. You should rule out flaky connections and solder joints by poking around with an insulated probe (stick) with the power on before you go after the capacitors. The synthesizer probably develops several DC voltages which should each be checked. Do you have a multimeter or oscilloscope? Do you have a schematic? Can you post a clear, well-lit (not flashed) picture of the power supply section?