No sound from Roland input section

Discontinued products Shruthi
#1

I get no signal from my Roland board and the problem appears to be in the input section. Since its different from the smr-4 I don’t really know where to look. The only location where I can find the oscillator signal is until the entry of R7. Right after R7 it gets quiet. The same signal should be on the other side of R7 no? So every pin of the TL072 is quiet as well.

What could it be? I’d say a broken resistor but that sounds ridiculous :slight_smile: Forgive me for being so clueless.

#2

Just found that if I take out IC2, the TL072, then there is a faint signal on the socket pins 1 and 2. It’s a lot softer then the input I measure just before R7.

#3

With IC2 inserted, no signal at pin 1 of IC2?

If so, check R5, R7, R4, C6. Check that the supply pins of IC2 are +5V and -5V.

#4

There’s definitely something wrong with the power supply. The resistor values and C6 seem to be correct, but the voltage at pin 4 is 0.68 instead of -5. The voltage at pin 8 is +5 like it’s supposed to be.

0.68 is also what I measure that the pin of C23

#5

Check your LT1054 . Its not a part you’d use in a Sojus - it breaks quite easy… Pin 5 should deliver -5V.

#6

I swapped it with a new one, but that didn’t make a difference. All the caps seem to be correctly polarized… That leaves IC3?

#7

I replaced IC3 with a new one, still no difference…:frowning: Any other ideas?

#8

Oops forgot to put back IC2 which I took out when soldering a new IC3. Power is ok now! So it was IC3 after all. I think I damaged it the first time when I soldered it backwards and turned it around. I must have somehow damaged it then.

#9

So I got things running and sounding ok. Hurray!

I tuned it but I noticed that the resonance pot has little influence on the oscillation. Is that normal?

Also what is the gate trimpot for? I couldn’t find any reference to it.

#10

The “gate” trimpot can be used to fix VCA bleed.

Set all oscillators to “none”, and resonance to the maximum value. Turn the trimpot until you hear the resonance self oscillation sound “bleed” through the VCA (the VCA should be shut but there’s still a fraction of the signal going through). Now turn the trimpot in the other direction and stop as soon as you have silenced it.