SOLVED Magnetron - Bypass and Dry signal but no delay

[LittleRummyTumTum]

I've just put together a Magetron, and as per the title I'm not getting any delay - bypass signal passes, and I get dry signal with the effect on, but no delays.
The modulation appears to be working, as the rate LED and I can faintly hear it doing something in the background.

At first it was making a ticking noise that was affected by the level and time controls, but not feedback - this has gone away after reflowing multiple solder joints though.
I've verified the pt2399 works as does so in another circuit (spirit box).
The internal gain knob also does appear to affect signal level.
Lower row of pots all have covers.
Pics below - any ideas or tips where/how to probe?


EDIT/UPDOOT: Found a solder bridge under an electrolytic - after fixing I now get one very quiet repeat, but that's all.

 

[LittleRummyTumTum]

Update: Found a solder bridge under an electrolytic - after fixing I now get one very quiet repeat, but that's all.
I've done some probing based on other threads and the following for additional info:

Feedback pot to C3 does measure 11k
All pots measure/work correctly
I can trace continuity through R4 -> C3 -> R8 -> R9 -> Feedback pot
I can trace continuity through IC Pin 12 -> R13 -> R15 -> IC Pin 13 -> Pin 14 -> Feedback pot

 

[music6000]

R17 -15K should be BROWN GREEN BLACK RED BROWN ???

 

[Nostradoomus]

scrub the board and take a picture without the flash, it makes orange look red etc. I can see a few wrong values but I don't know for sure. C17 for starters. Or is it C14? The build docs are different from the picture on the main page...paging @Robert

 

[LittleRummyTumTum]

R17 -15K should be BROWN GREEN BLACK RED BROWN ???

We have a bingo! A gremlin apparently replaced my 15k resistors with 1.5k (it's me, I'm the gremlin)

It now works, has far less repeats than it should (not any where near oscillation) but it works. The repeats will likely be corrected by...

scrub the board and take a picture without the flash, it makes orange look red etc. I can see a few wrong values but I don't know for sure. C17 for starters. Or is it C14? The build docs are different from the picture on the main page...paging @Robert

AHAH! It's 33n but should be 330n... I gotta stop mathing these out in my head. I'll try to pickup a substitute tomorrow and see if that fixes things. (The PCB silkscreen says 330n so I'm guessing it's c14.)

 

[Nostradoomus]

Go by the silkscreen for sure

 

[giovanni]

We have a bingo! A gremlin apparently replaced my 15k resistors with 1.5k (it's me, I'm the gremlin)

It now works, has far less repeats than it should (not any where near oscillation) but it works. The repeats will likely be corrected by...



AHAH! It's 33n but should be 330n... I gotta stop mathing these out in my head. I'll try to pickup a substitute tomorrow and see if that fixes things. (The PCB silkscreen says 330n so I'm guessing it's c14.)

I never trust myself doing the math in my head!

 

[LittleRummyTumTum]

Right! So replacing the 33n with the correct 330n has resulted in much longer and more expected delay times.

But now I have no modulation for some reason. Which worked fine before. Agaaghhghgdfsdds.

Any ideas?

 

[Nostradoomus]

Did you clean your board? Could just be stray solder splatter messing things up.

 

[LittleRummyTumTum]

Did you clean your board? Could just be stray solder splatter messing things up.

Yep. Gave it a thorough clean with iso alcohol. Also tried replacing the depth pot & led + subbed the LM258n for a TL072 incase that was fried and still no dice. The modulation LED isn't going either so my guess is it's LFO related, but I can't make sense of the LFO in the schematic (I am not a smart man).

 

[Nostradoomus]

Yep. Gave it a thorough clean with iso alcohol. Also tried replacing the depth pot & led + subbed the LM258n for a TL072 incase that was fried and still no dice. The modulation LED isn't going either so my guess is it's LFO related, but I can't make sense of the LFO in the schematic (I am not a smart man).

Check all values and continuity in this area. Voltages on the IC etc too. Stop replacing stuff lol

 

[LittleRummyTumTum]

Continuity was broken between C8 & the depth pot somehow. probably severed the trace internally with all my poking, prodding and bending pots back and forth, but a jumper solved it.

Protip: populating boards while watching youtube and hitting cones is a bad idea and a sign of overconfidence.

But, I officially declare this solved! Thanks all.

 

[music6000]

Protip: populating boards while watching youtube and hitting cones is a bad idea and a sign of overconfidence.

Rum & Raisins are known to do that!!!, stick with Vanilla.

Don't forget to mark this a SOLVED.
Edit on the left in Header of your first post.