Ampeg B100R again...

[g1]

TP4 is still -9.7 VDC ugh... TP1 -0.2 TP2 +13 TP3 -12
A bit discouraged here -what next?

Curious that TP1 went from being 0.002V to 0.2V when you didn't change anything there. I would be measuring voltages at the input of IC1 (pins 2,3) with no input.

Forgive me if I've lost the plot, but I don't recall TP1 (or 2 or 3) being discussed. Is there a typo anywhere? Are we all looking at the same schematic?

[glebert]

Forgive me if I've lost the plot, but I don't recall TP1 (or 2 or 3) being discussed. Is there a typo anywhere? Are we all looking at the same schematic?

IC1 pin 1 = TP1 (see post #16 and #28)

[glebert]

glebert - thanks for checking in and welcome to my nightmare...

IC1 Pin2 +0.2VDC Pin3 +0.2VDC

Those pins should be same voltage for an op amp, so that is good, but should be at 0 VDC. What are you using for your ground reference for these measurements? Not sure what would be pulling those voltages up. Sometimes chassis ground is not the same as signal ground, for example

[mtlbasslad]

Those pins should be same voltage for an op amp, so that is good, but should be at 0 VDC. Something is pulling it up, either at the op amp input or output. Wondering if Q1 could be misbehaving and pulling up the op amp output through D4?

You are wondering - I'm baffled... should i pull Q1?

[mtlbasslad]

Ok then, not pulling Q1. Going out to the shop now & stare at it... give it the evil eye, yeah that always helps LOL

[glebert]

You are wondering - I'm baffled... should i pull Q1?

I wouldn't pull it, but in the absence of anything else to try might as well measure voltages there.

[g1]

As IC1 was just replaced, and I think socket was added, verify all connections, orientation, and supply pins (4 & 11).

[mtlbasslad]

Yes, IC1 & socket added, all connections & orientation checked... IC1 Pin4 +14VDC Pin11 -14VDC

HELP!

[mtlbasslad]

Those pins should be same voltage for an op amp, so that is good, but should be at 0 VDC. What are you using for your ground reference for these measurements? Not sure what would be pulling those voltages up. Sometimes chassis ground is not the same as signal ground, for example

Chassis ground... there is no signal in these tests

[g1]

Do you have another TL074 to try? Even the original? It seems odd that with the new chip, all 4 output pins go bad all of a sudden.

[mtlbasslad]

Yes, with the price of shipping I ordered 2 of everything. Original was scrapped with an attempt to snip the pins - which didn't work out to well, snipped a few but unsoldered the rest.
I'll try that later - right now preparing for weather problems, it's been raining all day & tonight forecast is for 50-100 km/h winds. Anticipating power loss & midnight generator use as temps plummet...

[mtlbasslad]

Survived the storm, genny performed well during 18 hour power outage...

Replaced IC1 (TL074) TP5 is now +19 TP6 +19 TP3 -12 TP4 +9 TP1 -0.2 TP2 +13 TP3 -12 all other voltages no change...

[Jon Snell]

Back to basics.
If the output pin 7 is not at zero volts DC then either pin 5 or pin 6 is not at zero.
The inverting input mimicks the output and in turn is controlled by the non inverting input. If the inverting input goes high the output pin will go low. If the non inverting input goes high the output will go high and that should cause the non inverting input to follow the output, returning the output to zero or a multiple of the voltage applied to it.
https://www.electronics-tutorials.ws/opamp/opamp_1.html

[g1]

Please post all IC1 pin voltages.
Are all boards installed or floating/disassembled. I'm concerned about missing ground like glebert mentioned earlier.

[mtlbasslad]

@ John Snell - thank you for your interest, but way over my head. I'm just a hacker with a few good tools. Never got past point-to- point & tube amps.

@ g1 IC1 voltages with no signal, using chassis ground lug on power cord. Only one board which is installed, lots of jumpers required.

Pin 1 -0.02 to -0.07
2 + 0.4
3 + 0.4
4 + 14.5
5 +12.8
6 +11.25
7 +11.25
8 -11.25
9 +0.6
10 0.0
11 -15
12 0.0
13 -0.002
14 +8.9

Interesting D1 (peak LED) is on...