EH Small Stone Issue J debugging

[jokke]

1.What does it do, not do, and sound like?
- Sound goes through with the effect on, but no phasing effect at all.

2.Name of the circuit
- Electro Harmonix Small Stone EH4800 Phase Shifter, Issue J

3.Source of the circuit (URL of schematic or project)
- http://www.generalguitargadgets.com/pdf/ggg_smallstj_sc.pdf

4.Any modifications to the circuit? Y or N
- Yes, volume mod. R42 changed from 4k7 to 10k. Worked about 2 months after modding.

5.Any parts substitutions? If yes, list them.
- Stock parts.

6.Positive ground to negative ground conversion? Y or N
- No.

7.What is the out of circuit battery voltage? = 9,01V
Voltage at the circuit board end of the red battery lead = 8,75V
Voltage at the circuit board end of the black battery lead = 0,00V

Q1 = 2N5088
C = 8,12V
B = 2,33V
E = 2,02V

Q2 = 2N5087
C = 3,60V
B = 8,03V
E = 8,66V

Q3 = 2N5087
C = Oscillating something between 4-7V
B = Oscillating something between 4-7V
E = Oscillating something between 4-7V

Q4 = 2N5087
C = Oscillating something between 4-7V
B = Oscillating something between 4-7V
E = Oscillating something between 4-7V

IC1 = EH1048 = CA3094
P1 = 4,28V
P2 = 3,10V
P3 = 3,11V
P4 = 0,00V
P5 = 0,60V
P6 = 3,11V
P7 = 8,65V
P8 = 8,65V

IC2 = EH1048 = CA3094
P1 = 0,00V
P2 = 3,05V
P3 = 3,10V
P4 = 0,00V
P5 = 0,60V
P6 = 1,29V
P7 = 8,64V
P8 = 8,64V

IC3 = EH1048 = CA3094
P1 = 6,09V
P2 = 3,10V
P3 = 3,10V
P4 = 0,00V
P5 = 0,62V
P6 = 4,96V
P7 = 8,65V
P8 = 8,64V

IC4 = EH1048 = CA3094
P1 = 0,60V
P2 = 3,11V
P3 = 3,10V
P4 = 0,00V
P5 = 0,61V
P6 = 1,44V
P7 = 8,65V
P8 = 8,65V

IC5 = EH1048 = CA3094
P1 = Oscillating something between 1,6-1,8V
P2 = Oscillating something between 4-7V
P3 = Oscillating something between 4-7V
P4 = 0,00V
P5 = 0,56V
P6 = 0,56V
P7 = 8,65V
P8 = Oscillating something between 4-7V

[chromesphere]

Hi Jokke,

I had a problem with my small stone a while ago.  From my, very meager, understanding of the circuit, IC 1 - 4 should all have the same voltages (oscilliating), 4 stages causing the phasing.  IC 5 is the LFO...(Anyone please correct me if im wrong here.)  With my problem, i noticed IC 1 & 2 were corrent, but IC 3 and 4 were different.  I swapped IC 3 and 4, and found IC 1 2 and 3 were now correct, but IC 4 was not.  Seemed like a good guess to swap IC 4 with a new one, which i did, and it fixed the problem....anyway...Your IC 1 - 4 pin 1 and 6 voltages aren't quite right, suggesting a short, faulty component etc.

Basic troublshooting - dont know if you've tried this, but, usually where I start: I would first check for a short on the tracks, use a magnifying glass, they can be a hair thick.  So many times ive checked over my boards, all looks good. Then i take a knife to them (lightly) and all of a sudden they work.  Could be my sloppy soldering though If you used sockets and have spares, swap the IC's and trannies.  Make sure their seated properly.  Also make sure their in the correct way around.  Also check on the component side for any component leads touching, or bits of wire shorting out your circuit.  Sometimes the problem can be on the component side of the board. (This is how a non-electronics person like myself fixes his builds.)

No expert on the topic, but hope this information results in a fixed Small Stone for you all the same!

Good luck!
CS

[jokke]

Thank you for answer. I don't think that it's a solder bridge because this is a stock effect pedal from EH, and it's been working like a dream to this point. Of course i have been carefully examining all those traces.

I'm just asking about those voltages on ICs, like what IC should I change first. These aren't quite easy to get from Finland... Have to buy from eBay and it takes millions...

[chromesphere]

In that case i have no idea...

I would try using an audio probe and trace around the circuit.   However, I cant even tell you where to start.

Could also still be a short on the board somewhere, caused by a wire for example, although its probably more likely a faulty component / IC.

Unforunately thats the only (novice) advice i can offer.

Good luck all the same!
CS

[jokke]

Updates, good and bad things.

Good: One thing is sure, one of my EH1048 is broken. I installed IC-sockets for the 4 phasing stages. With swapping the IC's and using audio probe, I found out that guitar signal stops at one particular IC. It stops in that particular IC, even it is in any of those 4 stages.

The broken IC gets the singal on pin 1, but there's nothing on the output pin.

Bad: I have tested two different CA3094E to replace that broken IC, none of those work

Is it really possible to replace that EH1048 with CA3094E?