Another Sea Urchin problem

[muddyfox]

Hey folks!

I've just built a Sea Urchin according to this schematic and it doesn't work.


The only thing I did different was to connect PT2399 pins 3 and 4 because without that all the voltages were whack. Now only a few are. 
Here's what I've got:

PT2399
5.02      2.3
2.44      2.3
0      5
0      0
2.67      2.3
2.4 4     2.3
.66     0.8
.69     4.54

TL072
3.59      7.77
3.59      3.59
3.59      3.59
0         4.1

78L05
7.15
0
5.02

I'm guessing the values in red are kinda weird. I get clean signal on opamp pins 1 and 7 and on output. I also get clean signal on PT pins 9 and 15 and nice delayed (delay changes as I turn the delay pot) signal on pin 12. I have it on one side of R14 20k but not on the other. The other side is connected to pin 14 where I get 5V.

Normally, I'd just swap out PTs until I got one that works fine. It's kinda hard to do right now because my layout is SMD and I don't have a hot air rework station to easily remove it.  So I just thought to pick your collective brains before I try to remove it... could the problem be elsewhere? Any ideas?

[muddyfox]

No bites?

Wherever I look, it seems that the right side of the working chip is usually half the power supply. What would make my 9/10 and 13/14 be weird (other than a faulty pt2399)?

[madbean]

First I would look at why your supply voltage is so low. 7.15v from a 9v supply means something is amiss. Secondly, without any reference to your layout available, I would look for possible solder bridges between the pins on the SMD chips, or elsewhere. That 5v is coming from somewhere.

Lastly, I'm wondering why you needed to connect pins 3 and 4. They are already connected via a 10-20R resistor internally. I don't know if that is relevant to the problem or not, but it is worth pointing out.

[muddyfox]

Thanks for chiming in, Brian!

To address your points in order:
Here's my layout, front and back





Referring to the schematic and the layout, 9V from the power supply drops across R7 33R to the listed 7.15V. I'll try to check for solder bridges, they can only happen on ic's because the other components are so far apart that it would be pretty obvious and frankly kinda hard to pull off even if I wanted to.  That 5V must be coming from elsewhere, there's no 5V on any of the other pins.
Opamp ic is functioning properly, I'm getting signal on all output pins (so board output as well). It's just that the wet signal isn't getting back to the output for some reason.

I connected pins 3 and 4 (and I'm well aware of the internal 10R connection) because I had no other things to try. Without it the voltages were even farther off (for instance, I believe there was almost 2V on pin4) and I was getting no repeats on pin12 (now I am). Also, I found numerous references online to this, most notably here http://www.valvewizard.co.uk/smalltime.html

[muddyfox]

Reviewing my layout I just realized that I'm powering the opamp directly from the 9V and not from a point behind the R7 33R. The opamp doesn't seem to mind  but would it account for any of my issues?

[madbean]

A nearly 2v drop across a 33R resistor means something is wrong. What is the current rating on your supply (or are you using a battery)? IOW, the current draw on your PCB is either exceeding the available supply or perhaps you have used a 330R resistor...just thoughts...none of these things may be true.

I would start there...remove that resistor and bridge it to get your supply voltage up. That probably does not address the weird voltages on the PT2399, but it is a start.


---wrote the above before reading your last post. Pin8 of your op-amp reads 7.7v off a direct 9v supply. We need to figure out why. If it is connected directly to the supply then again, I think maybe the current output there is not enough.

[muddyfox]

I always double check all my resistors with a dmm prior to soldering (a time consuming hassle, but has saved me a few times) but I will remove the resistor and see what happens.
Would you recommend also disconnecting pins 3 and 4?

[madbean]

Nah, leave them connected for now. Mainly I want to see what happens when you take out that resistor.

[muddyfox]

Just saw your edit. I've tried powering it off a chinese wallwart (that I've never ever had problems with before) that powered a few DBDs I've build previously on vero without a problem. I've also tried powering it off a battery (half-dead, don't use them so I don't have a fresh one) but I'll get my 1Spot out so there's no doubt.

[muddyfox]

Well, I messed it up. I desoldered the R7 and bridged it, and with a 1Spot I got 9.31 on dc (and opamp and regulator). It still regulated properly to 5.02 as before and I still got 0/5V at pins 13/14. That 5V was seen all the way to the left of the C5, I have no idea where it came from (faulty pt?).

What's the mess-up? I tried snipping the pt off the board to replace it and in the process pulled two traces beyond repair. Luckily I have 9 more boards  but I might be missing some caps and stuff. I'm not sure I have spares for everything, will check tonight.

[stevie1556]

G, if you're missing any resistor or cap values, give me a shout. I think I should have everything for the circuit

Sent from my thumbs using Tapatalk!

[muddyfox]

Thanks man! Hopefully I'll get a chance to go through my stockpile tonight. I have gazillion of everything TH so this is kinda frustrating. :-)

sent from my mobile device

[muddyfox]

OK, I'm back. Took another board and populated. I shorted R7 (33R) and here are my voltages (different opamp this time around)

PT2399
5.07    2.46
2.46    2.46
0        5
0        0
2.72    2.46
2.46    2.46
.73      2.46
.75      2.46

NE5532
4.67      9.16
4.59      4.59
4.59      4.59
0          4.59

78L05
9.16
0
5.08

To me, things look ok apart from that 0/5V on PT2399. It's a different chip, all resistors and caps are new, yet the result is the same. Where does that 5V come from?

I'm gonna go over the schematic and trace the pcb but I'm rather pressed for time and it'll take a few days. Any ideas where I should look first?
Brian?

Thanks!