FIXED Recalcitrant Pork Barrel...

[wilsona]

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

[wilsona]

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

[wilsona]

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.

[RobA]

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?

[wilsona]

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.

[blearyeyes]

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.

[wilsona]

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.

[RobA]

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. 

[wilsona]

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.

[wilsona]

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.

[wilsona]

Here are the pictures.

[wilsona]

Another picture

[wilsona]

Last picture. Apologies for the 'hairs' - from a woollen blanket I put over the dining room table!

[RobA]

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.

[wilsona]

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?