Vintage MXR Phase 100 Troubleshooting and Repair Help

[JackthePineapple]

Hey y'all, this is my first time posting on this forum but I have learned a lot from you all about this particular topic. I'm hoping to contribute my piece to the topic of fixing old Phase 100s and get a little support on my project.

I have this vintage early 70s script logo Phase 100 that isn't working right and that I've been attempting to repair. I'd conservatively say I'm at the earlier stage of intermediate in terms of electronics know how, but I'm learning a lot with this project. I've been using this to learn how to read schematics and relate the schematic to the circuit diagram so I'm finding my way around. However I think I'm at a crossroads where I can't quite make out the next move. So I'm humbly requesting help from the folks here. Here's where I've been and where I'm at

First of all, here the schematic I'm using. It's the MXR 1977 schematic that floats around online which has been mostly accurate except mine seems to have an extra capacitor and a couple different part values.



Here are the gut shots of the pedal







Here's a shot of the component side of the board overlayed with the underside with the components labelled according to the schematic. I haven't mapped all the resistors, and I'm sure I got some of them wrong. But I am confident on the capacitors, Op-Amps, and Transistors. A main difference I found between my unit and the schematic is the number of capacitors (and some resistor values). I count 17 caps on the schematic, but 18 in the circuit. It looks like there are two 1uf caps for C1 in the circuit.



In the condition I received it in, the pedal bypasses, turns on, passes signal, and slightly modulates but the modulation is a very mild pulse. It's  more prominent on positions 2 and 4 but still not very apparent. It also oscillates/whistles. So this tells me there's an issue in the LFO circuit.

The trim pot had already been replaced with a 33k at some point and was my first suspect. The vactrols appear to have been replaced as well, but those seem to be working based off my measurements below. The modulation worked best when the trimmer was all the way clockwise but still the mild pulse. I replaced the trim pot with a 50k trimmer I had laying around which helped set the center frequency and fixed the whistling oscillation - so an improvement there. But the modulation still sounds weak.

In measuring some of the capacitors, mostly in the LFO circuit, the only outlier I found is C5 (15uf) measuring in at a whopping 139uf. I'm not smart enough to know what this means other than it's directly in the LFO, connects to the diode, and since it's so out of spec probably an issue. The measurements are noted in the overlayed image above but I will write them out below along with my measurements for the transistors, vactrols, and IC1 that's in the LFO. I measured the capacitors in circuit, but with no power running through and after the pedal had been sitting for about a week so I'm assuming it's misreading due to the capacitors not being discharged but I'm also not sure whether I should be measuring these out of circuit.

From what I can tell by comparing my measurements to others, specifically on this thread https://www.diystompboxes.com/smfforum/index.php?topic=68604.0 and https://www.diystompboxes.com/pedals/debug.html my transistors seem ok, although Q3's base isn't quite .5v higher than the emitter. And the vactrol voltages do oscillate (which gets faster as the Speed knob is increased) and the voltages do seem to step down 2v - 1.5v with each stage, so those seem to be working. So I am suspecting my issue might lie with C5 measuring so high.

I think my next step is to order a new 15uf cap to replace C5 and see if that helps. Does anyone have any thoughts on what might be going wrong that I'm missing? Thank you very much if you've made it this far and for the attention!

Measurements taken on a Klein MM420 DMM.
Using a CIOKS PSU set to 9v using a battery clip. Measures 9.22V at the red 9v+ wire to ground.

All voltage measurements are DC measured to ground.

Minimum SPEED - POSITION 1

C1 (There's seem to be two)
One measures 1.2uf and the other measures 1.6uf

C3
15.57uf

C4
17.39uf

C5
139.1uf


Q1
C. 0.792V - 0.780V
B. 0.593V
E. 0.00V

Q2
C. 9.20V
B. 5.83V - 3.25V
E. 5.30V - 2.77V

Q3
C. 4.81V - 4.64V
B. 1.01V - 0.95V
E. 0.57V - 0.53V

Q4
C. 4.81V - 4.65V
B. 0.57V - 0.53V
E. 3.1mV - 0.9mV

V3
LED+. 9.20V - 9.19V
LED-. 7.72V - 7.62V (0.10V variance)

V2
LED+. 7.72V - 7.67V  (0.05V variance)
LED-. 6.26V - 6.15V (0.11V variance)

V1
LED+. 6.26V - 6.16V  (0.10V variance)
LED-. 4.79V - 4.63V  (0.16V variance)

IC1
1. 5.00V
2. 4.87V
3. 4.81V
4. 0.00V
5. 5.85 - 3.20V
6. 5.82V - 3.34
7. 8.55V - 0.601V/0.00
8. 9.20V

Shout out to
Pedalbob
Mark Hammer
Govmnt_Lackey

You all have left some invaluable knowledge here over the years that I dug through which really helped me get my feet on the ground with this one. Specifically on the posts below:
https://www.diystompboxes.com/smfforum/index.php?topic=128117.0
https://www.diystompboxes.com/smfforum/index.php?topic=17542.0
https://www.diystompboxes.com/smfforum/index.php?topic=128014.0

[PRR]

suspecting my issue might lie with C5 measuring so high.

Probably not. C5 connects from V+ to Gnd. No signal/shake action. Like if you specified a 15 foot wide  bridge support and somehow found a 139 foot support. It's just better, and probably not to notice. (also you may have more V+ caps not accounted.)

What is the complaint? Weak wobble? Measure voltage on R39 (20r). Ah! First measure R39 be sure it IS 20r. A real wide swing could be 800mV to zero. If it wobbles faster than your meter will read, tack-solder a couple hundred uFd at C3 to make it r-e-a-l s-l-o-w. It's probably not 800mV, but if it only wobbles say 50mV that's a clue.
Those 16(!)-pin SN72L044 "op amp" chips bothered me, but apparently are kosher. That looks like a TTL part number but was changed the next year to TL044.
https://modwiggler.com/forum/viewtopic.php?p=1159766&sid=955075c7d24e7abf04c1388fc576edce#p1159766
See also in that thread the wooden switch.

[JackthePineapple]

Hey thanks for the leads PRR and for the helpful analogy. It is indeed a weak wobble complaint. I haven't had much time to dig back in deeply this week but I was able to check R39. R39 does read very close to 20k resistance which is good! DC voltage is wobbling between 2.5-0.7mV (!) though which is low. I don't have a working unit to compare and know what to look for but I'll start working backward from here and see if I can't find any component values amiss. Will update my progress

[PRR]

R39 does read very close to 20k resistance

R39 should be 20 Ohms, not 20 K Ohms!!

20 Ohms is an odd value; many sets start at 22 Ohms. OTOH many meters are bad about reporting the K, and users get confused.

> I haven't had much time

Take your time, read carefully.

And, sorry: WELCOME!!