SOLVED Aion Xenotron/? Flange LFO issues


Active member
I am really at wit's end about this one, and could really use some help.

Built the Xenotron to Aion spec with a lot of care, aside from the pin headers, for which I just used in-line sockets and clipped component leads.

Here is the schematic. As far as I can understand, it looks like there is a signal backbone ("space" aka what looks like a tremolo) that is effected via LDRs by LEDs (LED 1 & 2). There is also a "time" loop (aka the flanger which goes through v3207 and v3102 BBD and clock chips) attached which is also to some degree governed by LED/LDR interactions (LED 3 & 4). The LEDs in both are controlled by an LFO circuit.

Unlike the other Xenotron support group members, I have demonstrable modulation and self-oscillation in the circuit controllable by pots and trimmers, and LEDs 3 & 4 are on, but not pulsing. The Manual pot turns down the brightness of LED 4. The LFO rate pot affects the voltage in the circuit.

What I do not have is LEDs 1 & 2 lighting up, nor any pulsing, so I think something is amiss with the LFO. When I touched the anodes doing a continuity probe both LED 1 & 2 lit up and effected the signal via the LDRs. The status LEDs also brightened.

I have:
*pulled all transistors and ICs and reflowed all points.
*checked all transistors with my new component checker. Even though I don't know how to interpret the readings or recognize when something is out of spec, all BC549C and J113 had relatively similar readings. Can provide the readings.
*put in a new set of TL071IP chips, which are the chips in the LFO
*checked all continuity to ground, and all continuity between components in the LFO circuit. All continuity checks out.

pics to come.

Readings of essential elements in the LFO schematic, LFO rate pot full CW--I also have readings with it turned full CCW:
VC (LFO voltage): 8.612
VD (LFO reference voltage): 0.699

LED1: A: 6.43v, K: 4.936
LED2: A: 8.18v, K: 6.63v

LED3, which is on, reads A:8.18v and K: 6.31v. So I think I am missing something.

IC1 TL071IP:
1: 0.436
2: 1.670
3: 0.357
4: 0
5: 0.052
6: 0.357
7: 0.693
8: 8.18

IC2 TL071P
1: 0.006
2: 0.317
3: 0.357
5: 0.075
6: 0.357
7: 0.357
8: 8.18

Q10 (BC549C NPN)
C: 8.13
B: 0
E: 0

Q11 (BC559 PNP)
E: 8.18
B 8.17
C: 0

Q12 (J113):
D: 1.673
S: 2.839
G: 0

Q13 549c
C: 4.938
B: 0.006
E: 0

C: 6.63
B: 0.357
E: 0
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Ohhhhhh man.

It was indeed a problem in the LFO section.

Components are fine, except for two. Circuit and continuity is fine.

If anyone is interested in guessing what was the matter, don't scroll down. (hint: it has to do with the BOM and 2 very important components for the LFO)

I put TL071IPs in the LFO instead of TL022s. WHY??? just... WHY????!!! I don't know. I am extremely surprised, as I'm sure everyone must be amazed that the circuit works *exactly* *correctly* with the right components. So facepalm. And here I was casting aspersions on Aion. Check yourself when and before you wreck yourself.
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Nope! But close.... It's really stupid.
Well, that was interesting. I thought something was up with TL071s, but didn't think much because my brain probably thought TL072.
My other thought was that you had a wrong value near the power section, i e a 100k for 10k.

Congratulations on getting it working. Now to help others in non-working flanging hell
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I don't know how that short circuit happened--maybe I read TL072, and saw TL022 and thought "oh, that's not a TL072", and searched out the TL chip that I habitually see as not TL072, which is TL071. Who knows.

I actually had the same thought about the resistor, but I double-checked all the resistors I thought I could l have made an easy mistake on--and all I needed was just to read the damn BOM and the print on the chip! (although to be fair, sometimes it's really hard to read on the chip)