Edited after realizing I shouldn't use IN/OUT in the typical wiring.
I am using the "SND" as the input and the "RET" as the output.
I have no output signal. After probing, with tone at 50%, I have dry signal at both octocouplers, but nothing at C7 or C8, or anything after that in signal path.
My tap switch and LED are functioning and LED1 is lit.
My voltages look fine to me, but please feel free to check these:
TL074
1- 4.5
2- 4.5
3- 4.5
4- 0
5- 4.5
6- 4.5
7- 4.5
8- 4.5
9- 4.5
10- 4.5
11- 0
12- 4.5
13- 4.5
14- 4.5
LM356
1- varies
2- 3.3
3- 3.3
4- 0
5- 3.3
6- 3.3
7- varies
8- 5.0
TAPFLO
1- 4.95
2- 2.3
3- 2
4- 5
5- varies
6- 1.5
7- varies
8- 4.95
9- 2.5
10- 2.8
11- 2.2
12- 4
13- 2
14- 0
T1: O= 5, G= 0, I= 9.3
T2: O= 4.9, G= 0, I= 9.2
Edited after realizing I shouldn't use IN/OUT in the typical wiring.
Also, with my JMK test rig, I can crank my test tone volume and headphone volume way up and just barely hear the effected signal. Like if it were bleeding through somewhere. At this point, I have verified my component values are correct.
I have a working I haven't fully boxed up yet. I'll post my voltages tomorrow.
Do you have audio before the ldr? And after the ldr? Are c6 and c7 bipolar? Have you tried another tl074?
Hi Anthony,
can you check if your optocouplers are correctly oriented?
Check if you are getting a voltage variation on the LED side of the optocoupler and a varying resistance on the LDR side.
It might be just typo but can you check if you used a LM358 and not LM356?
Also voltage at pin 8 of that opamp seems low. It should be 5v + you LED voltage drop. Can you double check ?
pin 4 on your tl74 should be close to 9v. Can you double check your voltage?
I believe my octos are correctly oriented, I matched up the + on the component with the symbol on the pcb.
I am getting slight variation on the LED side, from 1.40 to 1.44, back and forth.
I did use LM358.
Pin 8 of that is 6.8v, must have been a bad reading earlier.
Pin 4 of TL074 is 9.2, I misread my notes.
ok that makes more sense at least :-)
could you try to measure the resistance of your optocouplers on the LDR side (on and off, use the square wave setting at full depth)
On square wave, full depth...
The LED side varies from 1.29 to 1.46
I'm not getting any reading on the LDR side, but I'm not sure if I am measuring it correctly. I am using the resistance setting on my meter and touching the probes to the two LDR legs of each octo. Is that right?
it might not work with every multimeter, measuring resistance in circuit while operating
in theory the optocouplers should be working, you have some voltage going into them.
If the signal stops after the optocouplers, you may have some short somewhere in that area
David, I sincerely thank you for your help.
I'm done with this for today. I'll check it over with fresh eyes and report back tomorrow.
Quote from: drolo on April 05, 2017, 10:11:39 PM
it might not work with every multimeter, measuring resistance in circuit while operating
in theory the optocouplers should be working, you have some voltage going into them.
If the signal stops after the optocouplers, you may have some short somewhere in that area
I rechecked all joints and components and don't see any shorts. I have audio at on leg of the LDR of the octocoupler, but no audio at C6 and C7. Looking at the schematic, it looks like this would be where the failure is since C6 and C7 come directly after the octocouplers. I pulled C6 and C7 to rule them out as a short. I am not getting any audio at their solder pads. Should I be able to hear audio with a probe there? I am using VTL5C1 vactrols. Like you said, they are getting voltage and audio, so it seems they should be working.
if you pulled the 2 caps out, now is a good time to measure the resistance of the optocouplers. Try to measure how it changes using the square wave at full depth with a slow rate your multimeter can cope with
Quote from: drolo on April 06, 2017, 07:49:10 PM
if you pulled the 2 caps out, now is a good time to measure the resistance of the optocouplers. Try to measure how it changes using the square wave at full depth with a slow rate your multimeter can cope with
I was able to get a measurement now. I get varying resistance on the LDR side, from 0 to 30m.
very strange ....
you said you had signal up to one leg of the LDR, is that thr left side, and then nothing on the right side of the LDR ? (if facing the PCB component side)
maybe some shorts to ground after the LDR's?
Just to rule out the possibility of the optocouplers having some issue (which I doubt) can you bridge the LDR's with a 1k resistor. and adjust the volume trim pot to see if you have any output
It is the same on both LDRs. I have tone set at 50%, on classic mode.
Am I correct that if the octos are working properly, I should hear audio with a probe at C6 and C7?
I could be crazy, but I'm starting to think my problem might be the test rig. I will take steps to rule that out tomorrow.
On my test rig, if I crank up the test tone volume and the headphone volume, I can barely hear proper effected signal.
Quote from: AntKnee on April 07, 2017, 03:24:14 AM
I could be crazy, but I'm starting to think my problem might be the test rig. I will take steps to rule that out tomorrow.
On my test rig, if I crank up the test tone volume and the headphone volume, I can barely hear proper effected signal.
Its not the test rig.
Am I correct that if the octos are working properly, I should hear audio with a probe at C6 and C7?
With C6 and C7 removed, I hear clear loud audio input and faint effected audio output at the optocouplers. I hear faint effected signal on the + pads of C6 and C7. If I insert C6 and C7, the audio dies. I am using non bipolar electrolytic capacitors. Are they the problem?
Here are the caps I used:
http://www.mouser.com/Search/ProductDetail.aspx?R=ECE-A1EN100Uvirtualkey66720000virtualkey667-ECE-A1EN100U (http://www.mouser.com/Search/ProductDetail.aspx?R=ECE-A1EN100Uvirtualkey66720000virtualkey667-ECE-A1EN100U)
so you mean, going into the optocouplers, you have a clear loud signal, but at the output pad of the optocouplers not?
For both of them?
If yes then there still seems to be something wrong around ldr's
Quote from: drolo on April 07, 2017, 02:41:09 PM
so you mean, going into the optocouplers, you have a clear loud signal, but at the output pad of the optocouplers not?
For both of them?
If yes then there still seems to be something wrong around ldr's
Isnt one side of the optocouplers the inverting input of an opamp? On mobile so going by memory here, but you wouldn't hear any audio there, you'd have to check the output pin of the opamp.
Then I suppose what is happening with my capacitors at C6 and C7 is fine.
Which pin would that be? (schematic posted earlier)
I have dry signal at pins 5, 6, 7, 8, and 14
Edit: C6 and C7 are reinstalled
(http://circuits.datasheetdir.com/37/UTC-TL074-pinout.jpg)
Quote from: midwayfair on April 07, 2017, 02:45:54 PM
Quote from: drolo on April 07, 2017, 02:41:09 PM
so you mean, going into the optocouplers, you have a clear loud signal, but at the output pad of the optocouplers not?
For both of them?
If yes then there still seems to be something wrong around ldr's
Isnt one side of the optocouplers the inverting input of an opamp? On mobile so going by memory here, but you wouldn't hear any audio there, you'd have to check the output pin of the opamp.
Actually the 2 signals are now decoupled with caps. (I was having some ticking issues with very low on resistance of certain LDR's) So it's still a mystery that there is sound at one end of the LDR's and not at the other if the resistance drops according to the LFO. Could you post high resolution pics of both sides of the PCB ? perhaps we'll be able to spot something.
(https://dl.dropboxusercontent.com/u/13215910/Web%20Images/twin%20peaks%20pcb/20170407_121456.jpg)
(https://dl.dropboxusercontent.com/u/13215910/Web%20Images/twin%20peaks%20pcb/20170407_121503.jpg)
(https://dl.dropboxusercontent.com/u/13215910/Web%20Images/twin%20peaks%20pcb/20170407_121653.jpg)
(https://dl.dropboxusercontent.com/u/13215910/Web%20Images/twin%20peaks%20pcb/20170407_121718.jpg)
What if the LED side isn't getting enough power? Since I have very faint audio at the effect output, maybe it is working correctly, but the octocoupler isn't getting bright enough?
Quote from: AntKnee on April 07, 2017, 05:31:16 PM
What if the LED side isn't getting enough power? Since I have very faint audio at the effect output, maybe it is working correctly, but the octocoupler isn't getting bright enough?
Let's try the following:
Set your depth knob to minimum.
Measure your LDR resistances.
I'm measuring about 28m on both, but it increases/decreases slowly.
Quote from: AntKnee on April 07, 2017, 05:59:19 PM
I'm measuring about 28m on both, but it increases/decreases slowly.
like 28 megaohm ?
Quote from: drolo on April 07, 2017, 06:04:33 PM
like 28 megaohm ?
Yes, that is what my meter is reading. If I change the range to ohms or kilo ohms, it only reads "OL".
Also, this is with C6 and C7 reinstalled, so I'm not sure if I'm getting a realistic resistance reading with the circuit operating.
Right now it looks like the resistance is not getting low enough to let any signal through
at half depth it should be low enough to let significant signal through.
Could you measure what voltage change you are getting at pin 5 of the taplfo (with depth full and square wave) should be between 0 - 5 v
Same for pin 1 and 7 of the LM358. swing should be 5v peak to peak centered around your 3.3 v reference
If you are getting these voltages, would you feel comfortable desoldering the LDR side of the vactrols to measure the resistance with them out of the circuit (leaving the LED side connected)?
Tapflo pin 5 gets 0v - 7.6v
LM358 pin 1= 1.34v - 5.43v
pin 7= 1.05v - 5.42v
I'll desolder the LDRs and measure the resistance later this evening.
David, thanks again for helping!
these all look good (except pin 5 of the taplfo which should never get higher than 5V but I guess it's a typo)
Quote from: drolo on April 07, 2017, 08:21:35 PM
these all look good (except pin 5 of the taplfo which should never get higher than 5V but I guess it's a typo)
I don't think its a typo. I better recheck values in the morning.
Definitely not a typo. I have 7.6v on pin 5 of tapflo.
I desoldered the LDR side of the optocouplers and checked resistance. I have to set the rate very slow to get a steady reading. I am measuring 20 megaohm max on #1, and 10 megaohm max on #2.
but does the LDR resistance get lower with the change of the LFO voltage ?
The LDR resistance goes alternates from 0 to the measured resistance in sync with my tap LED.
I just swapped out LM358 for a new one, and I now have 4.8v on pin 5 of tapflo, which also alternates from 0 to 4.8 with the tap LED.
I missed this on my first check: R47 and R48 are supposed to be 100 ohm, I have 100k ohm. Correcting that now.
Resistance at LDRs is now at 400k on #1, and 200k on #2.
After swapping R47 and R48 for the correct values, I am up and running.
I wish I would have noticed the resistor value when I checked all my components earlier. I'm not sure at this point if I also had a bad LM358 earlier, but I left my replacement in.
David, thank you for all your help throughout this troubleshooting. I greatly appreciate your help.
Yeayh ! :D
Good Job spotting that! ;)
Thanks again.
Build report posted!