Reddish 500 EQ

[MidnightArrakis]

Yes, I think we can and we should

Sounds like a plan. I have started a thread for it in the Machine Shop forum.

Cheers

Ian

[I have started a thread for it in the Machine Shop forum] -- What is this new thread called? How do I find it? Where is it located?

/

 

[capacitorless]

Seriously - you can't be bothered to navigate to the Machine Shop forum yourself and check the top?

"/" indeed.

 

[JMan]

For future readers who might run across this discussion at a point in time when Ian's thread is - perhaps - no longer at the top of the Machine Shop forum, here's a link.

 

[Forcemusicgroup]

Just completed this build. I purchased a set. I was able to get one running flawlessly however, the second one.... nothing. Passes signal in bypass but when active, I get nothing. I hear the relays going off. Can someone lead me through where to troubleshoot? I appreciate it. I haven't not tested voltages as I'm getting nothing to start. Any help would be great.

 

[JMan]

Testing voltages would be the place to start.

If voltages are good, the next thing I'd try is switching it to a different slot in your rack to see if that is the culprit.

These steps help us rule out the obvious (yet easy to overlook) variables. You'll want to do that first before we go hunting in the circuit.

The good news is that you have one unit running, so we have something to compare it to. Please report back once you've done the two checks above, and if the problem persists, we'll move on to troubleshooting the circuit.

 

[Forcemusicgroup]

Changing slots didn't help. Im using a tester jig. I'm getting 24v "in" and 0 in bypass.

 

[JMan]

Cool, so that's good. Did you check the +/- rails on the op amp?

 

[Forcemusicgroup]

No I haven't, please explain the steps.

 

[JMan]

Set your multimeter to measure DC voltage. Place black probe on the 0vdc pad on the edge connector, being careful not to accidentally short to either power rail. Then place your red probe on pin 8 (top right) of the op amp, where you should read approximately +15vdc (anything within roughly a 10% tolerance is within the realm of what we expect here, we're only worried about it if it's really far off). Then move the red probe to pin 4 (bottom left) of the op amp, where you should read approximately -15vdc.

 

[Forcemusicgroup]

Alright, Done the test. voltage on both

 

[Forcemusicgroup]

d1, d2,d3 is showing great voltage both +15vdc, - 15vdc. I checked c101,c102, checks good,

 

[JMan]

That's likely to be the issue. I'll ask you to check two things.

First, check that you have positive voltage coming into the module in the first place (again, multimeter to read DC, black probe on 0vdc pad, this time put the red probe on the V+ pad on the card connector right above the black probe, again being very careful not to short them).

Assuming the positive rail is fine, we'll do a continuity test with your multimeter. Turn off power or unplug the module from your test jig. Set your meter to continuity mode, and measure between the op amp pin 8 and each of the other seven pins. If you socketed the chip, I'd remove it and just prove the socket. If you have continuity with another pin, it likely means there is a short.

If neither of those tests yield anything out of the ordinary, we'll keep hunting.

 

[JMan]

d1, d2,d3 is showing great voltage both +15vdc, - 15vdc. I checked c101,c102, checks good,

Oh interesting. So the only spot that the V+ isn't showing up is the op amp. That definitely tells us something. Maybe a picture would be useful.

 

[Forcemusicgroup]

ok. so looking at the TI manual of the pin out of the op amp. PIN 1 and PIN 5 are showing continuity.

 

[JMan]

Okay, so just out of curiosity I just took out a new-in-box OPA2134 and measured to see if there was continuity between pins 1 and 5 (in case it was a normal condition of the internal circuitry). There is no continuity, which seems to reflect what the datasheet says.

Did you socket the chip or solder it directly to the PCB?

 

[Forcemusicgroup]

yep directly soldered.

 

[Forcemusicgroup]

ill have to replace that it may be faulty.

 

[Forcemusicgroup]

the working unit is doing the exact same pin 1,5

 

[JMan]

Oh, yep, I was at work and was not looking at the schematic, but now that I've had a moment to review it, Pins 1 and 5 are indeed connected in the circuit. I didn't remember that off the top of my head. Do make sure you're also referencing the schematic as we do the troubleshooting, it will help you avoid chasing your own tail.

So my initial interest was in whether Pin 8 had continuity to any other pin. I take it you confirmed that it is not shorted to any other pin?

 

[JMan]

It is tricky to troubleshoot a circuit from afar. I'm trying to think through what could be causing this. If you've got V+ going everywhere it's supposed to except the IC, I'm struggling to imagine why. Even if the IC were blown, measuring DC between that pin and the 0VDC reference should still show the positive voltage. Is there any chance that somehow the trace was accidentally cut during assembly? Perhaps the electrical connection was not made and you need to reflow the solder? Can you measure continuity between the op amp Pin 8 and the +16VDC pad on the edge connector?