Monarch accidentally received 18v

Chuck D. Bones said:
Not this time.
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Ok Chuck. I found the negative leg of c19 was pulled out a bit. I removed and replaced. There’s still something not right. The only way I can make it sound remotely like a distortion is with all 4 pots maxed and the boost engaged. Without the boost engaged it sounds like a weak overdrive. Changing c19 did change pin7 of IC1. All voltages on jfet’s were unaffected
IC1
1=8.42
2=8.42
3=0
4=0
5=4.26
6=4.60
7=4.57
8=8.96
 
Time to bust out the audio probe. We'll try a binary search. Listen to Q5-G. That's right in the middle of the signal chain.
  • If you get good distortion there, then we know everything in the first half of the circuit is good.
    • If distortion is good, listen to IC1-5.
    • If distortion is bad, listen to pin 3 on the GAIN pot.
Based on what you find, we'll proceed from there.
 
Chuck D. Bones said:
Time to bust out the audio probe. We'll try a binary search. Listen to Q5-G. That's right in the middle of the signal chain.
  • If you get good distortion there, then we know everything in the first half of the circuit is good.
    • If distortion is good, listen to IC1-5.
    • If distortion is bad, listen to pin 3 on the GAIN pot.
Based on what you find, we'll proceed from there.
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Got it. That will be my next move then. Thank you for your guidance
 
dlazzarini said:
I have faith.
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Here’s what I’ve got so far. At Q5-G I have sound. It’s not distorted sound. With the boost on it’s close to unity gain with my input signal. With boost off its quite a bit lower in volume than input signal. I then chose distortion is bad from your flow chart which took me to lug 3 of gain pot, where the signal is so small I have to struggle to hear it. I did a little poking around while following the schematic and I’ve got good strong undistorted signal through C5 and into the left side terminals of C6 and R9. Big drop in volume on the right side terminals and into R10
 
We're zeroing in on the problem. Look for shorts or bad solder joints around C6, C7, R9, R10 and the GAIN pot. With power off and GAIN set to zero, measure the resistance from GAIN pin 3 to ground. Should be around 500K. Measure each side of R9 to ground. One side should be around 720K and the other side around 1.72M.
 
Good morning Chuck. Reflowed solder joints on C-6,7, R-9,10. Inspected all around the area under high magnification and I see no signs of shorting or broken traces. Resistance at Gain pot=519k, R9- 736K right side, 1.73M Left side
 
That's all good. I'm trying to understand why you lose so much signal going thru R9.

What is you audio probe feeding? Should be something high impedance. The higher the better.
 
Chuck D. Bones said:
That's all good. I'm trying to understand why you lose so much signal going thru R9.

What is you audio probe feeding? Should be something high impedance. The higher the better.
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I’m actually using an old pignose with the probe. I’m using a looper pedal for my signal
 
The resistance measurements you made effectively confirmed everything except the turquoise circles (Q3-G).

The Pignose is unsuitable for audio probing because its input impedance is so low. If you want to continue using the Pignose, you need to insert a buffered bypass pedal between the audio probe and the Pignose so that the Pignose isn't loading the circuit under test.
 
Chuck D. Bones said:
The resistance measurements you made effectively confirmed everything except the turquoise circles (Q3-G).

The Pignose is unsuitable for audio probing because its input impedance is so low. If you want to continue using the Pignose, you need to insert a buffered bypass pedal between the audio probe and the Pignose so that the Pignose isn't loading the circuit under test.
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Ok I can try that. Just trying to avoid having to work upstairs in the bedroom, or lugging an amp head and cab out to the garage. I’ll try the buffer pedal first.
 
Make sure you know what the input impedance is for that buffer pedal. You can't tell with an ohmmeter, you have to inspect the schematic.
 
Chuck D. Bones said:
Make sure you know what the input impedance is for that buffer pedal. You can't tell with an ohmmeter, you have to inspect the schematic.
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Ok Chuck. I guess I’ve been having some senior moments. I’ve got one of those Positive Grid Spark amps that’s been sitting in my room for over a year. Totally forgot about. The audio probe should be ok going in to that one shouldn’t it? I tried it out but I don’t see a whole lot of change. I can definitely hear the signal better on lug 3 of the gain pot now but it’s still at a much lower volume than before R9. I can definitely hear it better though
 
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