I'm fixing a Mutron III and have done all kinds of stuff, including putting in some new opamps (I used IC holders and put the old ones back).
I thought it was bad opamps because the outputs on A3 and A4 were on 10 volts DC, pretty much the rails. The HP output has -7VDC + 2VAC. The DC may be feedback from the LP and BP outputs.
Now, I'm wondering if the problem is the LDR.
The input to the LDR is DC plus a triangle wave, which is the rectified and filtered version of the sine wave input. I believe that's what it should be.
I have a scope and have been doing simple tests, but this one is kicking my EE butt.
I tried varying R23, which is a variable resistor on the board, and have left it about half-way. It didn't seem to change much.
How do you tell if the LDR is bad?
Small Bear has Hamamatsu P873-13 replacements, but I'd like to be reasonably certain before ordering one.
Schematics are here
http://files.muziq.be/schematics/musitronics_mu-tron3.jpg
Thanks!
Ron
I thought it was bad opamps because the outputs on A3 and A4 were on 10 volts DC, pretty much the rails. The HP output has -7VDC + 2VAC. The DC may be feedback from the LP and BP outputs.
Now, I'm wondering if the problem is the LDR.
The input to the LDR is DC plus a triangle wave, which is the rectified and filtered version of the sine wave input. I believe that's what it should be.
I have a scope and have been doing simple tests, but this one is kicking my EE butt.
I tried varying R23, which is a variable resistor on the board, and have left it about half-way. It didn't seem to change much.
How do you tell if the LDR is bad?
Small Bear has Hamamatsu P873-13 replacements, but I'd like to be reasonably certain before ordering one.
Schematics are here
http://files.muziq.be/schematics/musitronics_mu-tron3.jpg
Thanks!
Ron