Decent vintage pedal score. Now to fix / refurbish. Suggestions?

[danfrank]

1 watt is fine but yes, 1/2 watt was what was originally in there. 1 watt won't "stress" the circuit any more. Check where the wires go to the bulb... The bulb "socket" is kind of chintzy and it's easy for both bulb contacts to short with one another. This is probably what happened to yours, that took out that resistor.
If you can't get it running and are in the continental USA, PM me if you'd like me to have a look. I can get it working again for you.

[Delicieuxz]

1 watt is fine but yes, 1/2 watt was what was originally in there. 1 watt won't "stress" the circuit any more. Check where the wires go to the bulb... The bulb "socket" is kind of chincy and it's easy for both bulb contacts to short with one another. This is probably what happened to yours, that took out that resistor.
If you can't get it running and are in the continental USA, PM me if you'd like me to have a look. I can get it working again for you.

Thanks. I'm in Canada, though.

Tech repair is really abysmal in the area of Vancouver, Canada. There are very few repair places, some of them are MIA half of the year, they're overloaded with work, and they're extremely picky about what they work on and usually don't want to work on the music gear that I need fixed, even when I have the schematic (I couldn't find anyone willing to do a phat mod removal on a Triaxis, even though I had Mesa's official instructions for it). Sometimes I've had something sit at one of their places for months, only for them to tell me they don't want to work on it and to come pick it up. Sometimes they don't do the right thing, and multiple times I've gotten a device back with new cosmetic damage or that was handled roughly. Getting something actually done, and done right here is a rarity, in my experience.

So, if anyone wants to start a tech repair service and know they'll get enough business, there's a desperate need for reputable tech repair in Vancouver, Canada.

[Delicieuxz]

Today I replaced the resistor in my Pro Flanger with a 1-watt 220 ohm, and I replaced the bulb, too. That changed the pedal from a basically-not-working pedal to one that works... mostly, in the auto-flange mode.

In the auto-flange mode, it sounds mostly right. But when playing with the neck or neck-mid pickup on my Strat, I get some distortion that's not coming from the amp and which persists no matter how much I lower the amp's gain and master volume.

Also in auto-flange mode, when switching the colour switch, I don't hear much difference at all. But I think it's supposed to have a very pronounced difference between the colour settings. Maybe one of the trimpots can address that.

And then in manual-flange mode (where the foot pedal is used to control the sweep), it doesn't adjust with the foot pedal until the very last bit of the heel-down area, and then it produces a high-pitched squeal when it's near the heel-down position.

Any suggestions or ideas?


General demo of pedal functionality after replacing resistor and lighbulb:

Manual-flange high-pitched squeal:

Distortion when playing in the neck and neck-mid pickup positions:

[Delicieuxz]

By adjusting the 25k trimpot in the centre of the pedal, I was able to add a lot more range to the harmonic emphasis control, and to make the colour switch have more contrast between the modes.

Another trimpot, the 100k one in the corner with another 25k trimpot, when I turned it up very high, added the high-pitched squeal to the sound in the auto-flange mode. So, I backed that trimpot off until it disappeared. Maybe another trimpot will let me dial out the high-pitched squeal while in the manual-flange mode.

I'll play around with the trimpots some more later.

[Delicieuxz]

I think I may have figured out the squealing.

The 25k "high limit" trimpot and the 100k "low limit" trimpot need to be in a specific relation to each other. If the difference between them becomes too wide, squealing will occur - first in the manual-flange mode, and then, if the discrepancy is wide enough, in the auto-flange mode.

Once they're within the necessary threshold, if the 100k trimpot is lowered, then the 25k trimpot also needs to be lowered, to keep them within the threshold. Otherwise, squealing will occur. And likewise, if the 25k trimpot is increased, then the 100k trimpot also needs to be increased to keep them within the threshold.

I should experiment to find out what the difference is for the sound if they're both set with the threshold overall higher up the trimpots' sweep, or lower down their sweeps.


The "harmonic emphasis" trimpot simply increases the intensity / thickness of the effect. If it's set high, the pedal will self-oscillate at higher "harmonic emphasis" settings.


The two 25k "unknown" trimpots could dramatically impact the sound, but if they're turned too far one way, they cut-out a lot of the desired effect, or make the sound weak. But pretty much anywhere I changed them besides where they already were increased the amount of distortion I was getting from the pedal while playing with the neck and neck-mid pickup positions. I didn't find a setting where they actually removed the distortion I was getting while preserving the desired flange effect. Maybe, like with the "high limit" and "low limit" trimpots, they need to be set to have a particular relation to one another.


The 100k "unknown" trimpot made no noticeable difference to me, no matter how I set it. Whatever difference it's supposed to make might be dependent upon how the other trimpots are set.



In this image, I've labelled all the trimpots in the Pro Flanger and what they seem to do.





So, now, two issues remaining with my Pro Flanger are the distortion and that the manual-flange mode sweep seems to be almost entirely within a tiny space of movement in the heel-down area of the pedal. The 85% rest of the sweep makes no difference. I wonder if this might be caused by how the photoresistor is angled. But in the auto-flange mode, the pedal has its proper range of sweep to incrementally adjust the rate of the LFO.

[danfrank]

Hi,
Glad you've made progress... I don't know if you have  an oscilloscope or a multimeter that measures frequency but the "high limit" and "low limit" pots need to be adjusted so the min frequency is 20kHz and highest clock frequency is 800kHz when the flanger is in manual mode.
Also, both LDRs need to be bent at a right angle so the face of both LDRs are pointed towards the back of the pedal where the pilot light is. This way, the black piece of tolex that moves when the foot pedal is moved will cover or uncover the LDRs.
The 2 "unknown" 25k trimmers by the SAD1024 IC are for adjusting the bias of each of the sections of the SAD1024. A scope really helps with this.
The "harmonic emphasis" trimmer adjusts the amount of feedback. Adjust so the outer HM control oscillates (or just before) when turned fully CW. Adjust to taste.
Color switch is for selecting positive (fuller sound) or negative (hollow pipe sound)  flanging.
Hope this helps.

[Delicieuxz]

Hi,
Glad you've made progress... I don't know if you have  an oscilloscope or a multimeter that measures frequency but the "high limit" and "low limit" pots need to be adjusted so the min frequency is 20kHz and highest clock frequency is 800kHz when the flanger is in manual mode.
Also, both LDRs need to be bent at a right angle so the face of both LDRs are pointed towards the back of the pedal where the pilot light is. This way, the black piece of tolex that moves when the foot pedal is moved will cover or uncover the LDRs.
The 2 "unknown" 25k trimmers by the SAD1024 IC are for adjusting the bias of each of the sections of the SAD1024. A scope really helps with this.
The "harmonic emphasis" trimmer adjusts the amount of feedback. Adjust so the outer HM control oscillates (or just before) when turned fully CW. Adjust to taste.
Color switch is for selecting positive (fuller sound) or negative (hollow pipe sound)  flanging.
Hope this helps.

That is very much helpful. Thanks!

My DMM doesn't read frequencies. But I might get one that does, or just have someone calibrate my Pro Flanger for me. Since I don't have an oscilloscope to bias the SAD1024 chip sections, I should probably take it to someone anyway. I assume they'll know how the two sections of the SAD1024 should appear when biased?

Do you also know what the 100k "unknown" trimpot that's on its own below the SAD1024 bias trims is for, and how it should be calibrated?

By the way, how did you come to know this information? Morley told me they received no documentation for the Pro Flanger when they bought the company, and its designer passed on years ago, so they couldn't help with it. They were happy to receive the Pro Flanger schematic which you gave me a link to, and one for the Pro Phaser, which I found elsewhere.

[danfrank]

I have forgotten what the unknown 100k trimpot does, I have to find my notes on the flanger to see what I wrote down.
This Morley flanger circuit is very similar to the old original A/DA flanger circuit and I've worked on the A/DA flanger so much in the past that I am well versed on its circuit.

[Govmnt_Lacky]

Do you also know what the 100k "unknown" trimpot that's on its own below the SAD1024 bias trims is for, and how it should be calibrated?

If you can use your multimeter to trace where the trimpot is connected to, then someone can establish (possibly) what its purpose is. If I were to guess without knowing, I would say it is an output balance trimmer for the BBD.

[R.G.]

Do yourself a favor - replace every single electrolytic capacitor in the unit. They go bad at a variable rate, even when not being powered. A unit that old will have very old electrolytic caps in it.
Be sure to observe proper polarity when replacing.