Ross Phaser from tonepad - not working

[kevinrontel]

I just put together a Ross Phaser using the tonepad schematic/PCB and it is decidedly non-functional.

When effect is "engaged", the signal passes thru with virtually no effect.  The only difference between engaged and bypass is a slight volume drop and teeny loss of treble when engaged.

It's the mod-free schematic here: http://www.tonepad.com/getFileInfo.asp?id=99

I don't have a very fancy voltmeter so the numbers below are rough (within .2 volts, I reckon).  Obviously, something is wrong.  I'm not terribly experienced (two mostly-working pedals under my belt) so the problem is likely me.  I'd be incredibly grateful for any recommendations on where to go next.
 
Power Supply 9.0 V

IC1
1- 4.6
2- 4.6
3- .2
4- 0
5- 3.6
6- 4.3
7- 4.4
8- 9

IC2
1- 1.3
2- 0
3- 3.8
4- 4
5- 1.2
6- 0
7- 1.2
8- 4.2
9- 4.6
10- 1.2
11- 9
12- 1.7
13- 4
14- 3.7
15- 0
16- 1.2

IC3
1- 1.2
2- 0
3- 3.6
4- 4
5- 2
6- 0
7- 2
8- 4.2
9- 4.5
10- 2
11- 9
12- 2.2
13- 4
14- 3.7
15- 0
16- 1.2

IC4
1- .75
2- 0
3- .75
4- 4
5- .5
6- 0
7- .5
8- .5
9- Fluctuates between 0 and 4.8.  Currently settled on 4.  Nope.  Now it's zero.  Is it possible that, in taking the measurement of pin 9, I shorted pins 9 and 10 and fried something?  It's 2 now.  
10- 9
11- 0
12- 0
13- 0
14- .5
15- 0
16- 0

[kevinrontel]

Based on previous Ross Phaser threads, it looks like pin 3 of IC1 is out of whack.  It should have around 4.5 v but shows only .2v.

IC4 looks all kinds of wrong.  I swapped ICs 3 and 4 to see if perhaps IC4 was bad.  The readings were essentially the same so I would conclude that the ICs are good. 

[ACS]

Sounds like a short or wrong value somewhere upstream of Pin 3.  A quick look at the schematic points to either the 10K or 470K either side of Vb.  Assuming that your other voltages are correct (and I stress this is an assumption!) the implication is that the 10K is correct.  Therefore, my guess is that the 470K is either the wrong value, or is shorted somewhere...

Worth checked around D1, D2 and the 0.01uF cap for shorts as well...

Good luck
Aidan

[kevinrontel]

Thanks, Aidan for your advice.  Using a better multimeter, I checked all components upstream of Pin 3 on IC1.  10K, 470K, the diodes and caps all appear to be good.  I touched up all the solder joints and checked for continuity on all traces in this same area.  I've found no shorts.  Pin 3 of IC1 continues to show ~.02 v. 

And IC4 is still fraught with its incorrect voltages. 

Any other suggestions?

[kevinrontel]

The pedal continues to not work and I continue to be too inexperienced to have a clue as to why it doesn't.  I did hook it up to a sine-wave generator and then run the output into an oscilloscope.  When the pedal is engaged, the signal is apparently flipping out of phase from the original input.  That was kind of neat.  But I still don't know why pin 3 of IC1 doesn't have the 4.5 volts it should have.  I did read a little bit about op amps, though so I know that it definitely SHOULD have 4.5 volts.  Given my vast ignorance, it seems far more likely that the problem is some as-yet-undiscovered mistake I made than it is a bad IC (I even used sockets!), but I suspect that, before I shelve this thing, I'll try a new IC just to prove myself wrong.

I also pulled one end of the 27K at the junction where the vibrato mod switch would go in hopes that it might isolate some thing or another.  I got a radio station to come in but nothing useful happened to the pedal and I didn't suddenly get smart. 

Oh, and per some random person's suggestion, I licked my finger and wiped it on the bottom of the board.  Some weird sounds came out when I got around pin 16 of IC 4.  Sort of phasey sounding in fact, but without repeating themselves at any kind of predictable or desirable frequency.  Which would sort of make sense since that's right at the LFO pot.  Then I decided the wet finger technique was probably stupid so I stopped. 

Anyway, I think I'll go enroll in an electronics class now.

[kevinrontel]

Replaced IC1, the 470K resistor, and the .01 cap, checked polarity on everything for the thousandth time, checked for shorts, confirmed that diodes are doing their job, touched up all solder joints, plugged it in, and...

Anybody wanna buy a populated Ross Phaser board that apparently has nothing wrong with it except for the fact that it doesn't work?

[kevinrontel]

It works now. 

I set it aside for a few months, worked on some other projects, got a little more experience and then gave it another go.  There were two problems.  First, there was a cold solder joint on a resistor.  The other, more significant problem was that one of the LM13600 ICs was dead.  Or partially dead. 

When I was originally struggling with this pedal, I switched all three of the LM1300s to different sockets and they all showed the same readings.  I therefore assumed that they were all working.  But when I fixed the resistor joint, the pedal would work when I rubbed a wet finger on certain parts of the board, but only when the ICs were plugged into the sockets in a certain configuration.  I replaced what I assumed to be the bad IC and the thing started making its pretty swishy sounds.

LESSONS:

1)  Make sure your work area is well-lit.  (The cold solder joint was totally obvious...when I took my work outside on a sunny spring afternoon).

2)  If something goes wrong, check continuity in a systematic fashion. (I found the cold joint by checking every single joint, one by one).

3)  Licking your finger and wiping it on the bottom of the board is a great way to sort of learn where and why things may or may not be working. 

4)  You CAN substitute the NE5517 chip for the LM13600 (or LM13700) in the Ross Phaser (I used this one: http://www.mouser.com/Search/ProductDetail.aspx?R=NE5517ANGvirtualkey58410000virtualkey863-NE5517ANG)

5)  I am now confident that I can assemble any pedal in the world using the paint-by-numbers technique and NEVER HAVE TO LEARN ANYTHING ABOUT ELECTRONICS.