Did I smoke my Juno-60 LFO?

[Helihammer]

Hi!

New here and just picked up a Juno-60. During cleaning, I noticed that the LFO trigger on the bender board wasn’t working. Took a look at the service manual and figured I would just short the high side of the LFO trigger (pin 18) to ground. Upon further inspection, I realized that the pin is not grounded when the LFO trig button is pressed but rather, it gets connected to the -15 V rail of the power supply.

On the bright side, I think the LFO trig switch is OK because I see -15 V on both switch terminals in Auto mode and the voltage on pin 18 changes from -10 V to -15 V when the switch is pressed in manual mode.

However, after grounding pin 18, I now can’t get any interaction from the LFO with the DCO or the VCF (both LFO sliders do nothing). The LFO will still modulate the PWM.

Reading through this thread

viewtopic.php?f=5&t=96487

I think the LFO trigger issue might be transistor TR20, but I’m unsure what ICs are keeping the LFO from working. Really hoping they’re some of the $0.25 TI ones and not the unobtanium Roland ICs!

Did I smoke the LFO when I grounded the trig line? I have a copy of the service manual, a DMM, and an oscilloscope and I’m not afraid to dig into the synth because I already have it apart for cleaning / foam replacement.

Any help would greatly be appreciated!

[Helihammer]

I suppose I should have mentioned that the LFO was working correctly before I shorted pin 18 to ground.

It would both modulate the PWM and and affect the DCO as well as the VCF - Both LFO sliders had an effect.

I see no waveforms on pin 20 of the bender board (LFO signal pin).