Roland SVC350 Vocoder Low frequency hum issue

Synth Repair
1

Hi

I have Roland SVC 350 Vocoder and suddenly it started work weird and hearing some weird low frequency hum (or harmonics?)

check the sample below please

Does any one have where this sound come from?

Thanks

2

Hums are to do with capacitors not being able to filter power supplies properly. The SVC350 is an old vintage 1980’s unit and its capacitors are time expired now.

If you have not done this before, its best to take it to a tech for it to be done. If you are capable start with the power supply caps. first. Also consider any diodes in the power supply section too. As capacitors age and allow more current to pass. This usually over taxes the diodes in the power supply.

If there are any tantalum capacitors in the design, consider replacing them with electrolytic ones. Tantalum caps explode at end of life or short without exterior signs.

Retest the board at this point if the hum still exists. If it does then its time to change all the rest of the electrolytic caps.

As for the rest of the circuit board. Any resistors that look burned or discolored, replace them. Power resistors in the 1watt to 5 watt range check for proper tolerances and change the one out of tolerance.

There are two other reasons for hums, failed or intermittent resistors capacitors which you look for by tapping on the component and listen to the output for noise increases, That is the most troubling to find. ground loops, is the last cause but is not likely in this case.

3

Thank you so much for reply!
I’ve brought it to tech before but he didn’t know where to start since he didn’t have any experience with SVC350 so I took it back. but I think he might be able to do it with your description.

Thanks a lot!

4

Old old tech trick coming at ya. Go buy a can or two of freezit. Spray suspected components one at a time and listen. If the component is failing it is usually going to generate heat, freezit will keep failing components from immediately making distortion and passing higher voltages. This is good for “failing” component identification. Failed, bulging capacitors , shorted and burned components replace by eye…they look bad so replace them. I also tended in older gear to use a signal injector and start from output signal and work backwards thru the circuit to finger failing components due to signal loss.