Harbinger 1.5 LFO Not Oscillating (SOLVED)

[Thommo]

(1) Harbinger 1.5 Univibe. 9v with charge pump version.

(2) LFO is static. Bulb lights and is active with the Gain and Offset trimmers. C/V and V/M switches are good. As are the Volume and Intensity controls. UniVibe effect is present with manual manipulation of the bulb trimmers.

(3) Found a short thread here with a similar problem. One or both MPSA13s being the culprit. I removed mine, replaced with sockets. Tried a few different sets with no change. When first powered, the bulb comes on brightly, with a very slight pulse. Then dies down to the trimmer settings and remains steady with no pulse. I also tried a different Speed pot with no change.
I've taken voltages as per the build doc, pictured below.

(4) No part or value subs were made. When looking over the board, I did find a couple of mistakes, which have been rectified.

[Zerro]

First clear with some mean (needle) pcb from tin dust at both sides - it can do many undesirable bridges.

[madbean]

All your resistors in the LFO section look correct. You've subbed 3k3 for the two 4k7 and that should be fine.

Two avenues to pursue:
The three 1uF electros in series could cause the LFO to die if any one of them is faulty. First try remelting the pads for those caps. If you have a continuity checker make sure there are no shorts in the caps, too. Possibly one or all might need to be replaced but always save that as a last measure result.

Second - since you have the two transistors socket, try subbing a non-Darlington for Q12. Maybe a 2n5088 or 2n3904. Possibly something is sinking current causing the LFO to stop operating.

Does the lockup happen if you leave the Rate control in the middle?   

[Thommo]

Thanks for the tips, guys! I'll try them out and see how it goes.

Yes, Speed pot set to 12 o'clock, as per the calibration method in the build doc.

Cheers,
Thommo.

[Thommo]

Alright, got it going!!!

I checked the row of electros. #1 all good, #2 all good, #3..........22uF
It must've somehow found it's way into the 1uF drawer. Or I absentmindedly grabbed the 22uF. Obviously overlooked it in the 78 times I went over all the parts, lol!!

Thanks for steering me in the right direction🤙🤙  I really appreciate it!

Cheers,
Thommo.

[madbean]

Alright, got it going!!!

I checked the row of electros. #1 all good, #2 all good, #3..........22uF
It must've somehow found it's way into the 1uF drawer. Or I absentmindedly grabbed the 22uF. Obviously overlooked it in the 78 times I went over all the parts, lol!!

Thanks for steering me in the right direction🤙🤙  I really appreciate it!

Cheers,
Thommo.

That's awesome that you got it solved! Just goes to show - a little thinky power on a problem can go a long way to making the rock and roll happen Good for you.

[Thommo]

Absolutely 😀

Now I've just got to do the same with my Forum Vibe build! No wet signal on that one.
It can wait, though.

Thanks again👍