Hi,
Looking for some help. I have just built a Pork Barrel (26/9/11 release) but it is not working and proving hard to diagnose. 3101/3007 version. Bypass is OK (!). I am using the indicator mod - LED does not light up at all when pedal activated or depth pot turned up or down. LED tests OK with a battery. I have checked all connections, cap orientation, values, and the board for shorts....
I would be most grateful for any ideas on what it might be or suggestions on how I can test it further.
Thanks,
AMW
More info:
ICs Pin 1
IC1 4.44v
IC2 varies 3.2v - 5.7v
IC3 9.1v
IC4 8.71v
2N5088 JFETS:
Q1 E 3.37v C 9.25v
Q2 E 3.69v C 9.25v
Q3 E 3.48v C 9.25v
Q4 E 0v (!) C 6.08v
Q5 E 3.99v C 9.1v
Hi,
I really would appreciate some advice on troubleshooting the chips in this pedal - MN3101, MN3007, TL062, JRC4558. Pinout voltages, etc. I think the 3007 might be faulty but don't know how to test it.
Thanks.
You're probably going to need the voltages on all the pins of the IC's and the base voltages on the transistors to help figure it out. Also, good photos of the PCB are very helpful.
But, the first thing I'd suspect is the LED wiring. It seems from the pin voltages you do have that the LFO may be working. So, it would seem that the LED should be working even with no signal going through. Are you using the standard madbean wiring for the footswitch?
Quote from: RobA on July 13, 2014, 01:15:21 PM
You're probably going to need the voltages on all the pins of the IC's and the base voltages on the transistors to help figure it out. Also, good photos of the PCB are very helpful.
But, the first thing I'd suspect is the LED wiring. It seems from the pin voltages you do have that the LFO may be working. So, it would seem that the LED should be working even with no signal going through. Are you using the standard madbean wiring for the footswitch?
Yes standard wiring but with the 'two for one' depth mod - the LED brightness is supposed to increase as depth knob turned up and also flash at LFO speed. It does neither. R39 omitted and LED is connected to rightmost R39 pin through a 22K resistor to +ve and -ve to 'sw' on 3PDT. LED tests OK on battery.
Definitely need all voltage readouts from your ICs and Trannies. Must have clear photos of your soldering on the solder side of the board. You can use a scanner to do that, I have heard. Try to get them as in focus as you can. I built one of these and was lucky it worked, and I love it, so hang in there!
Where did you get your 3007?
P.S. the only way to test the 3007 is to have a working circuit to test it in.
Will do - but might not be able to do this till the weekend.
On thing that confused me with this design is the pot pins - the board component side has pins 1-3 left to right, but standard wiring diagram has pot pins 3-1 left to right looking at back of pot. so you could not have pots mounted direct on PCB (by bending them upwards) and have the component side 'up'. I have wired it as per the standard wiring diagram 1-1, 2-2, 3-3. - should I try reversing it ? (Luckily I socketed all board connections.) I have attached the component side and std wiring diagram for reference.
The layout for the board mounted pots looks right to me. The pots sit on top of the back of the board with the pins pointing to the top of the PCB and the pots' bodies pointing towards the center of the board. So, that would make the orientation that the numbers give correct.
The pots are both 100kB, so even having them on backwards wouldn't make the pedal not work. In this case, since they are linear, it wouldn't even make the controls bunch up or anything. The only thing it would do is make the control's rotation backwards.
One additional thing to get a voltage on is either side of the new resistor for the mod and then the side of the LED opposite the resistor connection. Get a photo of the 3PDT switch wiring if you can while you are getting the other photos.
OK - I see what you mean about the pots, if they are PCB mount ones that makes sense - I was thinking of standard pots with pins bent up so they hang in front of the PCB, not reversed and behind the PCB.
Here are the full measured values (both pots max) - image since I can't format the text!
I've measured across the LED resistor incorrectly - I will update it tomorrow.
Here are the pictures.
Another picture
Last picture. Apologies for the 'hairs' - from a woollen blanket I put over the dining room table!
It looks like you've got pins 5-8 on the IC's in reverse order. The pin numbers go in a CCW circle and pin 8 would be the supply voltage pin on the op-amps. Still, I don't see anything on the IC voltages that jump right out at me. I've converted mine over to a MN3207, so I can't make direct voltage comparisons.
The thing that looks the most suspicious is what's happening around the LED and the 22kΩ resistor. I think that you would need the pedal engaged to get this measurement with the mod in place.
I will have a look again at measuring either side of the resistor tonight. I may also socket the other side of R39 and just plug in a 4k7 as per the non-mod design and see what I get.
Any comments on whether R1 is required?
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.
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.
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...
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?
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.
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.
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.
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.
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.
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.
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 (https://dl.dropboxusercontent.com/u/24630132/PCB%20-%20Rear.jpg)
Quote from: blearyeyes on July 19, 2014, 07:38:12 AM
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 (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.
Quote from: RobA on July 17, 2014, 10:01:01 PM
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?
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.
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...
Trace the input path now.
Start at the emitter of Q1,
Then the output side (+) of C2,
Pin 1 of IC1 (output of the buffer stage),
Junction of C8 and R14,
Base and emitter of Q2,
Pin 3 of IC3, (the input to the MN3007)
If something fails at any of these stages, narrow it down further by looking at the parts on the schematic between the last good location and the one that failed to have audio. You could reverse the order I listed above to and maybe find it faster. If you have audio all the way to pin 3 of the MN3007 and nothing at the output (7 and 8 ) and nothing on the base of Q3, then you need to start looking at the voltages around the MN3101 and the MN3007 again. Start with trying to rebias the thing and looking at the level of VB (should be measurable at the + side of C23).
Edited: I noticed that my 8 followed by a ")" got changed into a 8), so I edited to make it more clear what I was actually trying to say.
Quote from: RobA on July 20, 2014, 04:48:36 PM
Trace the input path now.
Start at the emitter of Q1,
Then the output side (+) of C2,
Pin 1 of IC1 (output of the buffer stage),
Junction of C8 and R14,
Base and emitter of Q2,
Pin 3 of IC3, (the input to the MN3007)
If something fails at any of these stages, narrow it down further by looking at the parts on the schematic between the last good location and the one that failed to have audio. You could reverse the order I listed above to and maybe find it faster. If you have audio all the way to pin 3 of the MN3007 and nothing at the output (7 and 8) and nothing on the base of Q3, then you need to start looking at the voltages around the MN3101 and the MN3007 again. Start with trying to rebias the thing and looking at the level of VB (should be measurable at the + side of C23).
Thanks - great info. I worked backwards as suggested. Here are the results:
Audio is present on PIN 3 of MN3007 and on base and emitter of Q2. Nothing at the outputs of MN3007 or the base of Q3. I tested the latter two at all points in the range of the bias pot.
I cannot get at the plus side of C23 or the legs of the trimmer from the component side - is there another point I can use? e.g. one side of R42, R43?
I can fairly easily replace C23 or the trimmer.
Here are re-measured voltages on the MN3007 and MN3101.
MN3007
1 8.7
2 4.75
3 3.74
4 0.6
5 0
6 6.7
7 7.07
8 7.07
MN3101
1 9.14
2 4.68
3 0
4 4.75
5 0.36
6 8.02
7 2.99
8 0.6
Voltage at the right side of R21 varies between 2.19V and 7.01V (same as left sides of R42/43 respectively) as the trimmer is turned. I take it from this that VB is in an acceptable range.
I wish I had I Pork Barrel build that I could check to compare your voltages with, but I've converted my build over to an MN3207. VB should be around 4.5V (half supply really). So, the range you have there looks good and should be plenty to dial in the level that your BBD needs.
The levels on the IC's look mostly OK to me, but pins 6, 7, 8 on the MN3007 look high. Other builds I've seen have the voltage at 7&8 closer to the half supply point. Pin 6 of the MN3007 should be the same as pin 2 of the MN3101 and yours are different. I don't know how much time lapsed between your readings on those pins and if anything else changed that would explain the difference, but it's suspicious and worth looking into further.
When I looked at the jumpers in your photo, I first thought they seemed suspect, but when I followed the trace in the doc, it seemed to me that the solder bridging that was possible there was just going to a pad that had a trace anyway. But, since we can't see the top of the board for those jumpers, maybe there is something that could be wrong in that area. Do the jumpers go through to the other side of the PCB? It does seem that there is possibly something wrong in the are of the MN3101. It would be worth reflowing those joints and checking for continuity on the pins that should be connected there and testing for bridging on pins that shouldn't be connected.
Thanks - They do go through to the other side. I will have a look but the IC socket hides them. I think I might cut the socket out, clean up and redo the jumpers and surrounding area and replace the socket. The readings for both ICs were taken at the same time.
Removed the M3007 socket, cleaned it all up and and redid the jumpers. Biased VB to 4.5V. No change. I've ordered a new MN3007 and MN3101 and will report back when I have replaced them.
Replaced the main chips - dang! No change. Don't know whether that's good or bad.... Probably means there is not much wrong but it's a b*gger to find. I'll stare at the schematic for a while and see what pops into my head. All suggestions gratefully received. Last thing I did was measure VB at R21 which is 4.49V.
Thought I'd check the diodes first. For D3 I am getting reading both ways on the diode check setting on my DMM: 0.465 and 1.955 - Is this correct? I was expecting to see a reading one way only. Checking a new 1N4001 gives 0.496 one way only. The other two diodes 1N914 give readings one way. D4 is omitted for this config.
For a 1N4001 you should only get a forward voltage drop in one direction. But, you can't check the reverse direction in circuit because there are parallel resistive paths to ground in the circuit and that will change the reading. If you were actually getting a 2V drop in the reverse direction, I think your power rail wouldn't be good and it does seem to be fine.
Have you found known good voltages for the IC's anywhere? I did a bit of a search around the forum for them, but I didn't see any that looked to from a verified working pedal.
It definitely seems like the issue must be around the MN3101 or the MN3007, or possibly the parts the connect the LFO to the MN3101. Have you checked for stray continuity between the pins of the two IC's and checked that the pins that should be connected are?
I have a working Pork Barrel (not boxed) and will post the IC voltage readings tonight....
I retested the voltages and I think they are OK.
Regarding continuity between the 3101 and 3007, I think its OK -
Pin 2 of 3101 -> Pin 6 of 3007
Pin 3 of 3101 -> Pin 5 of 3007 -> GND (?)
Pin 4 of 3101 -> Pin 2 of 3007
Not sure about pin 5 of 3007 marked 'Out 1.1' on schematic, this is definitely grounded.
No other pins on 3007 and 3101 are connected together.
Quote from: blearyeyes on July 24, 2014, 09:31:52 PM
I have a working Pork Barrel (not boxed) and will post the IC voltage readings tonight....
Thanks, I will look forward to it.
This is with a bench supply exactly at 9v. I built a charge pump and am going to run it at 15v..lots cleaner.
IC1
4.64v
4.64v
4.63v
.2mv
4.637v
4.64
4.63
8.98
IC2
vary 1.8-8.2
vary 4.46-5.46
vary 2.6-5.6
0v
vary 4.46-5.46
vary 3.0-5.8
9v
IC3
8.9v
4.55v
0v
4.55v
300mv
8v
vary 2.8-3.2
597.5mv
IC4
8.89v
4.56v
3.91v
597mv
0
4.54v
4v
4v
Google the chip numbers and get the spec sheets they will shed light on how they are integrated into the circuit. The power pins and the grounds etc..
IC3 (3101) my results look almost identical.
IC4 (3007) all except 7 and 8 (4V) which at my last reading were both 6.63V
Any ideas what could cause the difference?
I will compare IC1 and IC2 later today.
Forgot to add my readings taken with both pots max.
Quote from: wilsona on July 25, 2014, 08:00:05 AM
IC3 (3101) my results look almost identical.
IC4 (3007) all except 7 and 8 (4V) which at my last reading were both 6.63V
Any ideas what could cause the difference?
I will compare IC1 and IC2 later today.
Forgot to add my readings taken with both pots max.
The pot settings usually.
OK - so were your readings taken at max?
no I could do it again.
Just 7 and 8 of the 3007 IC4 would be useful.
Regarding IC 1 and 2 my results are much the same although I am not getting as much variation on those pins with a varying voltage on IC2. e.g. Pin1 I get 3.5-6.0 while the range posted by blearyeyes is 1.8 - 8.0
I think I am going to go through what has been done and post a summary of what we have and see if it rings any bells. The fact that input to the 3007 has audio present but output ( 7 and 8 ) has nothing must mean that the issue is either between the chips or between the 3007 and further along the path to main output.
I don't know this for sure, but it feels like pins 7 & 8 need to sit close to the bias voltage. And that high a voltage seems to me that it would be too high to set the bias for other parts of the circuit. I'd check all the areas around the jumpers again and the connections for R20 and R20 itself. I'm not sure you can measure R20 in-circuit, but it might work.
I just had a thought, maybe the BBD's you have just bias high. Perhaps you can get to the bias point if you try to run the input power at 12V. I think it would be worth a try if you've got a 12VDC supply around.
R20 one side relative to gnd measures 6.6V - same as 7/8 of 3007. I presume this is what to expect.
Across R20 measures 1.95V
The other side relative to gnd measures 8.7V
I don't really know what that means, tbh.
I redid the jumpers area and replaced the 3101 socket, reflowed all socket pins - unfortunately I do not know which pads to check that jumpers are connected properly.
I think I only have an 18V PSU around, I'll have a look.
You can see where the jumpers hook things to in the little inset. For the MN3007, the jumpers will make it so you have pin 5 going to ground and pin 1 and one side of R20 connected to pin 1 of the MN3101 (and the + supply voltage).
The one side of R20 and pins 7 & 8 should be at the same voltage, it just seems that 6.6V is pretty high, but I don't know what's in the normal workable range or if it is the BBD that is primarily responsible for setting that voltage level.
Might need comma in that sentence. I am reading it as -
"pin 5 going to ground, and pin 1 and one side of R20 connected to pin 1 of the MN3101"
I have:
One side of R20 is the same as 7 and 8 of 3007.
Pin 5 of 3007 -> gnd
Pin 1 of 3007 -> one side R20
I do not have one side R20 -> Pin 1 of 3101
Yeah, I could have said that better. Pin 5 should go to ground. The junction of Pin 1 on the MN3007 and R20 should be going to VD. Pin 1 of the MN3101 should also be going to VD. The inset diagram shows the jumper going to a trace and that trace continues on to Pin 1 of the MN3101, so you should have continuity from the junction of Pin 1 of the MN3007 and R20 (which coincides with the top jumper) and Pin 1 of the MN3101.
Yeehah! Found it. At last. Thanks everyone for all of your help in narrowing it down and pointing me in the right direction. I have learned a great deal about debugging and to be honest, although tearing my hair at times out I have quite enjoyed the process.
Don't know whether it was a PCB fault or the result of my inexpert soldering and subsequent redoing of the jumpers, but the pad on the jumper indicated on (blurry) attachment was not making proper contact with the track. I bridged it with a little solder till I got consistent continuity between all points. Once assembled again readings on pins 7 and 8 were just under 4V as required.
Pedal is now working. Does not like to be driven with a high input however. Distortion evident at a fairly low level. I'll try it before my compressor. Sounds great though, brings back a lot of memory associations. Ah, the 70's!
Thanks again for all of the help, I am am extremely grateful.
Ah, victory! Congrats, on getting it working. It can be frustrating and fun at the same time.
Now you have to come up with something to build for that extra MN3007 ;).
Yes - I might look around for another chorus board that uses that combo. Got PCBs for trembulator, cupcake, runt, rangemaster and bloviator (?) to keep me busy - already built an Umble, Afterlife and an 'order flipper'. My pedal board is now too small! Would love to build a fully featured multi loop pedal management project, not seen anything that ambitious in the hobbyist realm yet.
Feels good to finally find it! Congratulations!
Add a Road Rage and run it at 15 volts, it is much cleaner. That's what I decided to do cleans it up much more headroom. Also added the Tonepad cap mod. Better. Changed resistor 39? To 47k from 4k7. Starting to remind me of my CE-2 that I never should have sold..
I think JMK has a pedal looper system that might be of interest.
http://jmkpcbs.com/product-category/epic-bypass-looper/
I do have a spare road rage board, might have a go, although not much room left in my case.
I've just added the depth LED mod but not as good as I hoped - the LED flashes and gets more intense but the depth seems less. Will lookup the tonepad cap mod. Can hear the LFO ticking in background, need to look into shielding....
This Italian company do a kit: http://www.aresaudio.com/picolooper3.html
Thanks for your help - zeroing in on the output voltages got us there in the end.