Mutron III Opto Ckt. lights LED but no Env. induced brightening

[petemoore]

  Any clues...seems to lowpass, highpass, and bandpass the input signals, without any sweeping.
 Our drummer handed me the Mutron III and asked if I could take a look and try to fix it.
 I have an inclination it's 30+ YO age and the electrolytics are acting up, the Pignose or something is making cap-like drainey noises.
 It steadily lights a red LED w/1k5  circuit when I touch the circuit to the bulb leads, but no brighter or dimmer when everything that'd make it change lumens is tried [strumming, knob cranking/dialing/switching]. Obviously there's no change in R of the LDR's either.
 
   The bulb driver opamp voltages:
  _ DMM lead to pin 4:
 1=21.6
 2=10.6
 3=13.8
 4  DMM reference
 5=5.6
 6=1.7
 7=1.6
 8=22.4
 Any clues about the conditiion of this opamp/circuit ?
 I copied these because the outputs and inputs are 1/2, and they're so close I got lazy and said +/- 5%...looks biased, I can't read what I'm typeing so will leave it alone.

 
  1= 10.4
  2=11,4
  3=11.4
 
  5=11.3
 6=11.4
 7=11.4
 8=22.4
   1= 10.4
  2=11,4
  3=11.4
 
  5=11.3
 6=11.4
 7=11.4
 8=22.4
 

[Brymus]

Hey Pete I was just thinking about one when I saw your post.
Sorry I cant help you,but
If you can and it isnt much trouble.
I would greatly appreciate some pics of that original pedal,inside and out.
Do you know what the circled component is ? and what it could be replaced with today ?

[R.G.]

 Any clues...seems to lowpass, highpass, and bandpass the input signals, without any sweeping.
 Our drummer handed me the Mutron III and asked if I could take a look and try to fix it.
 I have an inclination it's 30+ YO age and the electrolytics are acting up, the Pignose or something is making cap-like drainey noises.

The Neutron filter is a more or less exact replica of that. All of the references to the Neutron auto filter apply.

Also, read the section of GEO's Guitar Effects FAQ on resuscitating the elderly effect. Don't suppose the electrolytics may be bad. Replace them and quit worrying. Remelt all the solder joints.

It steadily lights a red LED w/1k5  circuit when I touch the circuit to the bulb leads, but no brighter or dimmer when everything that'd make it change lumens is tried [strumming, knob cranking/dialing/switching]. Obviously there's no change in R of the LDR's either.

That tells us that the section that detects the signal level isn't working, yes?
 

The bulb driver opamp voltages:
  _ DMM lead to pin 4:

It uses a +/- supply with reference to signal. Put the DMM minus lead on the input jack ground terminal and measure again.

Do you know what the circled component is ? and what it could be replaced with today ?

The Mutron III is the original that supplied the circuit for the Neutron. Reading the Neutron literature gives you the answer. It's a Hamamatsu LED to dual/isolated LDRs. One LED, two LDRs. Small Bear stocked the identical item for a while, I think they're out. The alternatives are documented in the Neutron literature.

[Brymus]

OK thanks RG

Hope you get it sorted Pete !

[petemoore]

  I noticed a lot in common with the Neutron, having built/worked with it proved helpful in the d-bug.
   Wasn't sure what kind of light was used...figured it's an LED.
  I'm trying not to skip any steps on this one, including this thread, the electrolytics are on order.