Ross Phaser Voltages? Help.......................!

[modsquad]

Okay I am in the process of debugging my phaser and need to determine the proper voltages on the ICs.  I used the Tonepad layout for the PCB.  Here are what I have measured:

IC1
1   4.2
2   4.2
3   2.73
4   0
5   4.14
6   .16
7   .02
8   9.03


IC2
1   1.24
2   0
3   0
4   0
5   .004
6   0
7   .006
8   1.833
9   6.9
10  8.02
11  8.97
12  3.05
13  4.11
14  4.09
15  0
16  1.23

IC3
1   1.23
2   0
3   4.83
4   4.85
5   5.97
6   0
7   5.98
8   4.84
9   6.86
10  5.85
11  8.9
12  5.33
13  4.83
14  4.83
15  0
16  1.23

IC4
1   .59
2   0
3   .78
4   6.73
5   .59
6   0
7   .59
8   3.75
9   3.75
10  2.1
11  8.86
12  2.78
13  3.82
14  7.16
15  .62
16  1.06

Now I am not sure what the voltages should be based on the datasheets that I looked at.  I know the ground pins and the supply voltage pins but that's about it.  If someone could shed some light on these.  I am not getting any signal out.

Thanks,
Stan

[modsquad]

bump

[gez]

Could you link to the schematic?  Going by memory, a few readings look off, but I'd need to see the schematic to be of any help.

[modsquad]

Look here:

http://www.tonepad.com/getFile.asp?id=99

[gez]

IC1:  Pin 3 is possibly your meter's impedance pulling down the bias resistors, though it should be same as pin 1/pin 2.

Pins 6 and 7 are out, but probably due to trouble further up the line as the mixer is DC coupled

IC2:  This definitely has a problem

pins 3&4 should be at around the same voltage as the output of IC1a, not 0V.  Check to see they're not shorted to ground and that they're connected up properly.  The second half of the chip is a little squiffy, but you'd expect this as IC2a is out.

IC3:  IC3a looks ok

IC3b doesn't: it's output is slightly high.  Sometimes if you scrape between traces where the power traces connect up to the chip this sorts things out (minuscule bridges from power to the OTA's outputs - even if they have really high resistance - can screw the bias up).

IC4: Pin 1&16 of  should be same voltage (couple of diode drops).  Is the LFO working??  What are the symptoms?

Off to bed now...

[modsquad]

Right now I get no sound at all out of the darn thing except on bypass.  I will use the info you gave me to start tracing the circuit back from the pins and start there.  Thanks again for the help I am anxious to get this thing working.  Any other ideas let me know.

Stan

[gez]

Right now I get no sound at all out of the darn thing except on bypass. 

Concentrate on IC2.

[modsquad]

Okay I have sound now.  No oscillations though.  Just a compressor sort of effect.  I fixed the voltages on IC2  pin 3,4 are 4.86. 

[gez]

OK, re-post all your voltages, lets see if the rest of the circuit has biased up alright now that that section is fixed - just because you're getting signal doesn't mean to say each allpass stage will work correctly once you get the LFO working.

As for the LFO, the voltages for IC4 are totally out:

Pins 3 & 14 are connected so should be the same voltage

Pins 7 & 8 are connected so should be the same voltage

Pins 4, 9 & 13 are connected so should be the same voltage.

Not that these pins will be static when it's working mind (a good sign is when your readings fluctuate).

Check your joints.  Reflow if necessary.

Pin 1 is concerning me.  Its voltage should be around 2 diode drops (a little over 1V).  Haven't checked the PCB layout, but give the area a scrape between this pin and neighbouring traces (might be bridge of high resistance to ground pulling the voltage down).  Also check value of resistor from V+ to pin 1.

Could be that IC4 is toast.  Try the above and if all else fails pull it, give the spaces between the traces ( ) a scrape and solder in another.

[modsquad]

New voltages are:

IC1
1    4.5
2    4.5
3    2.73
4    0
5    4.34 
6    4.34
7    4.27
8    8.71

I am still trying to get pin 3 around pins 1,2

IC2

1  1.24
2  0
3  4.87
4  4.87
5  5.4
6  0
7  5.34
8  4.32
9  4.38
10 5.6
11 8.78
12 5.46
13 4.34
14 4.27
15 0
16 1.2

IC3
1   1.23
2   0
3   4.33
4   4.33
5   5.47
6   0
7   5.45
8   4.34
9   4.68
10 5.35
11 8.47
12 5.33
13 4.33
14 4.33
15 0
16 1.23

IC4
1   1.2
2   0
3   .78
4   3.77
5   .59
6   0
7   .59
8   .59
9   2.1
10 2.1
11 8.86
12 4.38
13 2.55
14 6.23
15 .62
16 1.06

I will work with IC4 and check all the joints and flows.  The thing I notice about these small boards is that the traces are close together and its real easy to melt a trace off or connect two traces inadvertanly.

[gez]

IC1 is fine (your meter is pulling down pin 3 when taking a measurement, so don't worry about that reading)

IC2 fine

IC3 fine

IC4 is all you need to concentrate on now.  The reading on pin 1 is fine now (chip should be ok) and at least 7&8 are same voltage, you just need to get this part (the LFO) kickstarted.   Keep working on it: scrape between traces and reflow joints.

[modsquad]

Okay finally got back to it.  Now my voltages on IC4 are:

1  1.11
2  0
3  1.5 to ? Jumps around (oscillating?)
4  Jumpy
5  Jumpy
6  0
7  Jumpy
8  Jumpy
9  Jumpy
10 Jumpy
11 8.9
12 8.9
13 Jumpy
14 Jumpy
15 0
16 1.09

[gez]

It looks as though you've got the LFO going now. 

If it's not sweeping the audio path you need to check the connections between the 10k coming off pin9 of IC4b and the Iabc pins of the other LM13600s (pins 1&16 of each chip).  Try reflowing the joints.

Edit: also check that it is 10k and not a larger value

[modsquad]

Its a sweepin the audio.  I replaced the resistor and added a sweep control.  I used 500k audio pots for the controls.   I find that changes in the sweep, regen and rate are only noticible across a small range of the pots.   I don't know if thats normal or not.  I like the sound though.  Subtle

Now I need to figure out why my univibe switch is not univibing.  I made a small board and connected an led, substitute capacitors and 3pdt to it to swap the caps for the univibe mod.   I attached the common to the middle lugs of the switch and other ends to the pcb.  I then attached the top row to one set of caps and the bottom row to the other caps.  When off I get phaser, when on I get boost but no univibe.  Oh well one thing at a time.

Thanks for your help Gez, you really simplified things for troubleshooting, plus I learned a few things along the way.

Stan

[gez]

May your notches be forever deep!