FIXED Recalcitrant Pork Barrel...

[RobA]

R1 isn't needed for the pedal to work correctly. It's good to have it there though and it won't alter the sound in any hearable way. You could move it up in value to 2.2M or something too.

[wilsona]

OK - getting somewhere - put R1 in 2.2M, socketed other side of R39 and put a 4K7 in. Then I found a short on the on the 3PDT switch - dang! sure I had checked that all out.... Whoop! Getting some action. However, it is all concentrated at the very end of travel of the depth pot, which also sharply affects the volume, the chorus effect quite quiet with thump of LFO in background - unusable! Also get silence at both ends of the depth pot travel. I took the pot out and it measured fine. So progress - yay! - but still stumped. I think there is something awry in the depth circuitry, since putting the mod back in I get no LED at all, at any point in the travel of the pot, even when I am getting some chorus effect in a small range at the high end of the pot. While I have the PCB out I'm going to check everything in that area of the board.

[wilsona]

Puit it back together again - and guess what - no chorus effect whatsoever. Absolutely no difference in sound or volume between effect in and effect out, pots don't do anything. It's like bypass/bypass. Feel like consigning it to the bin...

[RobA]

I wouldn't give up on it yet. It's probably something simple to fix but hard to locate.

Was it working completely before you but it back in? Did you put it back in with the mod in place or was it still in the stock configuration.

It sounds like there could be something wrong with the 3PDT.

Do you have an audio probe?

[wilsona]

I took the depth pot out to check it then put it back in. It was working a bit as I described before I did that without the mod which I left out. I don't think I have another 3PDT switch but I will have a look and replace it if I have one. I can make a probe but would not know where to apply it.

[RobA]

To use the audio probe, you just trace the schematic on the board and listen at the key points of the schematic. Inputs and outputs of the op-amps, etc. In this circuit, you've got the too audio paths too, the wet signal through the BBD and the dry.

But, the main reason I was asking in this case was to use it on the 3PDT and the input and output of the board, just to get an idea if there is something wrong with the switch or switch wiring.

Do you have a continuity setting on your DMM? If you do, use it to test the integrity of your 3PDT. Check to see if you have continuity when the switch is engaged to that side and then check the other side. Also, check to make sure you don't have any shorts between lugs that aren't supposed to be connected.

[wilsona]

My meter has an audible continuity tester which I do make extensive use of - 3PDT switch seems as if it is working OK to me, although it is weird that atm the sound is the same with effect both in or out. Not even a thump when switching, or a volume change. One thing I did note was that the voltage change across R39 is not very much when the depth pot is  turned up, so I wondered if this is worth looking into. I will drag it out again tonight and wrestle with it some more. Unfortunately with components on it is quite hard to trace the circuit - I don't think there is an etch graphic available for this PCB version which is double-sided.

[wilsona]

Fiddled with it for a couple of hours, checked the 3PDT switch, etc. I cannot get back to where I had it before taking the pot out, checking it and putting it back in. Oh well.

Indeed the values for the ICs were in the wrong order - corrected sheet attached.

[wilsona]

Hitting head off wall again. Since I had them, I replaced the 3PDT switch, the TL062 and the JRC4558. Still the same... I would appreciate if anyone with knowledge of this circuit could explain to me how the sound can be the same with effect both in or out, no apparent change? Its as if the input is going straight to output... If I knew where to probe I could give it a try.

[RobA]

The effect has two paths, the clean signal and the vibrato from the modulated delay line. If the delay line path isn't coming through, for whatever reason, there won't be any effect. The non-delayed path is designed to as unaltered as possible.

Have you tried re-biasing, since you've made all the changes? It'll probably need it at this point.

To probe the effect just follow the schematic. To see if the modulated path is working, start at the MN3007. Check to see if you are getting input signal on pin 3 and output signal on pin 7 and 8.

[blearyeyes]

This looks like a problem if there are traces on the other side of the board...
https://dl.dropboxusercontent.com/u/24630132/PCB%20-%20Rear.jpg

[wilsona]

This looks like a problem if there are traces on the other side of the board...
https://dl.dropboxusercontent.com/u/24630132/PCB%20-%20Rear.jpg

I have checked with DMM around this area and the jumpers test OK. In any case the circuit did work a bit briefly, so if this was an issue it would not have worked.  I am happy to test this again if someone can point out exactly where the jumpers should and should not connect. 

[wilsona]

The effect has two paths, the clean signal and the vibrato from the modulated delay line. If the delay line path isn't coming through, for whatever reason, there won't be any effect. The non-delayed path is designed to as unaltered as possible.

Have you tried re-biasing, since you've made all the changes? It'll probably need it at this point.

To probe the effect just follow the schematic. To see if the modulated path is working, start at the MN3007. Check to see if you are getting input signal on pin 3 and output signal on pin 7 and 8.

Making an audio probe this weekend. Intend to use my phone as an audio source and a modified PC speaker to amplify the ouput.

Jus to be clear I should get output (identical) on both pins separately 7 and 8 of 3007?

[RobA]

Yeah, pins 7 and 8 are tied directly together. When listening to it at that point, remember that the audio won't sound great because it's before the reconstruction filter.

The output from your phone should be OK, but the input audio shouldn't be more than a couple of hundred millivolts in amplitude.

[wilsona]

OK. Built a probe and it seems to working a treat. I am getting nothing on 7 and 8 of the MN3007. Don't know if significant but on first probe I get a loud crack, then silence on subsequent probes. When I then go back and check the input signal (to board or jack), first time I get a crack plus the audio. Subsequent probes no crack, just input audio.

Where else on the circuit should I have audio, either clean or fx? Please bear with me, I am not particularly up on reading schematics...