so i smoked my univibe last nite......

[Ben N]

We are normally very careful not to touch the tip of a soldering iron - even cold! - so we don't notice if it's got some leakage. Touch this to a circuit that has any path to ground and you get AC line leakage. It's a very plausible explanation.

Yup. I toasted my first 25 watt RS iron when I stretched my arms while working in my parents' unfinished basement and inadvertently touched it to a water pipe. Ah, memories...

[pinkjimiphoton]

good times, ben...lol... amazing the stuff we survive in our youth.

cheers to not being a statistic!! 

[pinkjimiphoton]

hello again.
went back in for more punishment tonite. found that r34 was ok, but... r33 was wayyyyyyyyyy off. supposed to be a 47k to ground, when i pulled it, it was reading 3.3k!!  i replaced it with a 47k from my stash of parts and fired her up to check voltages.
pretty much everything stayed within about a half volt or less change, but i think its cuz its cooler right now so the draw off the grid is less.  the adapter was reading 17.1vac tonite... which i assume accounts for most of the minimal <if at all> changes.
q 1-9, no change

q10 a huge change tho
from
c   15.1 to 15
b   1.7 to 6.0... <should be 4.7, so i should go to maybe 33k for r33, right? bleed a little more voltage to ground, or am i missing something? close enough for rocknroll?
e  1.1 to 5.5
pretty humongous difference, and the bias off a smidge, but better.

still no blinky blinky tho, but that may be due to the wrong kind of transistor subbing for the bd.

q11,12 same. e on 12 dropped from 20.0 to 19.6v

and of course now ldr 4 is reading 6.0 volts too

r13 changed a little bit,
b  2.5
c  19.3
e  2.0   still seems way off to me. but again, i know nada about oscillators n stuff. i am a fuzzbox guy

i thought perhaps the three leds i was running were sucking too much current so i disconnected them, too, to see if that had any effect with the lamp. no difference in voltage anywhere.
so will hook it back up.

soooo.... thats where i stand now. may have to wait for the lamp driver transistor to arrive.

happy 4th rg and all my fellow americans. come hell or high water,  i love the people in this country.
peace to all
gnite

[R.G.]

went back in for more punishment tonite. found that r34 was ok, but... r33 was wayyyyyyyyyy off. supposed to be a 47k to ground, when i pulled it, it was reading 3.3k!!  i replaced it with a 47k from my stash of parts and fired her up to check voltages.

And that's likely to be all that's wrong with the phase line, and probably the audio. I think you've fixed the Q10 problem.

still no blinky blinky tho, but that may be due to the wrong kind of transistor subbing for the bd.
[...]
q11,12 same. e on 12 dropped from 20.0 to 19.6v

I think you're going to have a working unit when we find the issue with the oscillator. The lamp driver isn't all that hyper-critical.

[pinkjimiphoton]

rg, question... could the capacitance inherent in the ribbon cable to the pot possibly be affecting the oscillator and making it nor run?

i will have to get back to this tomorrow, you guessed it, gig tonite.  there's really not much more in the oscillator is there? should i check the resistances in there, and the caps? its pretty much just the two transistors <last nites voltages were with the mpsa13's in the darlington config, no diff voltage wise with 5088> and the pot and a couple passives.

tomorrow when i get up i'll try and see if i can suss it out some more. thanks for the help sir!!

[Perfboard Patcher]

q1
c  1.6
b  1.3
e   1

q2
c  4.5
b  1.6
e  1.4

q3
c  11.2
b  4.5
e  3.9

OK PJP, so there is only 0.6 volts across q1. Plus there is a voltage gain of 4 divided across the first 2 transistors. That explains the distortion, there is hardly any headroom available for the positive half of the signal.

r13 changed a little bit,
b  2.5
c  19.3
e  2.0   still seems way off to me. but again, i know nada about oscillators n stuff. i am a fuzzbox guy

Yeah fuzzboxes have 2 advantages over LFOs. One can listen to them and they produce an image when watching the signal by oscilloscope.

Do you know the resistance of the lamp in operation? According to the info in the pdf the resistance of the lamp varies between 150 and 300 ohms (40-80mA at 12 volts). If you measure the resistance between emitter and ground you can calculate the current through the lamp and subsequently its resistance.

still no blinky blinky tho

Now the way I understand it ideally there should be 6 Volts across the lamp when there is no signal input from the LFO. The signal from the LFO should make the voltage across the lamp fluctuate between 0 and 12 Volts. One needs to know the output level of the LFO. And if the LFO is working at all    The voltage gain of the lamp driver I would assess based on the ratio of the resistances Lamp:(Tr1+R48).

[pinkjimiphoton]

thanks bro. so the ONE ldr reading 6 v is right, and the others are all low.... wonderful. think i may need to strip off all the electros, check the resistors and start over. bugger! lol

picked up a couple gigs over the weekend, so will be a couple days before i can get back to it. thanks for all the help!!!

[R.G.]

rg, question... could the capacitance inherent in the ribbon cable to the pot possibly be affecting the oscillator and making it nor run?

Hmm. I don't think so. The inter-wire capacitances are down in the tens to hundreds of pico farads, probably. The capacitors that set the oscillation frequency for the LFO are big, and attached through 4.7K resistors to one end to the emitter of the darlington on the other. Those low impedance points would push the frequency where the interwire capacitance up so high that the overall amplifier loop wouldn't oscillate.

Er... I think.     But that's an excellent guess.

i will have to get back to this tomorrow, you guessed it, gig tonite.  there's really not much more in the oscillator is there? should i check the resistances in there, and the caps? its pretty much just the two transistors <last nites voltages were with the mpsa13's in the darlington config, no diff voltage wise with 5088> and the pot and a couple passives.

I wish I could still gig. Sigh. It's the old tradeoff - learn more electronics and surrounding techniques, or practice and play your guitar. I'm pretty good with my decision to run down the electronics side, especially since I figured out that I have no real talent beyond rote memorization of licks. But still - playing in public is more addictive than heroin IMHO.

Yeah, check the values of the R's and Cs. Or, in something as simple as the LFO is, get out a full kit of new parts, test them out of circuit for all being good, then clip off the leads of the stuff on the PCB and pull out the leftover stuff in the holes and just re-manufacture it. For small, simple sections of circuits, with mysterious ailments, this is an old tech dodge that trades a few new parts. It's only really good for small, simple subsections, where it's about equivalent to swapping a new IC into a socket. But where you can trade debugging time not spent for the cost of Rs and Cs, it may be a good choice.

thanks bro. so the ONE ldr reading 6 v is right, and the others are all low.... wonderful. think i may need to strip off all the electros, check the resistors and start over. bugger! lol

picked up a couple gigs over the weekend, so will be a couple days before i can get back to it. thanks for all the help!!!

Again, I suspect that the audio path at least works. Concentrate on the LFO first.

[pinkjimiphoton]

thanks RG, i gotta gig again tonite  lol.... that said, i got the new bd's in today.
so i am gonna replace ALL the electros that aren't already replaced, as i suspect they all went down. seems safer, especially after learning the voltages are that far off on the ldr's.
will also replace all the components in the lfo and hope the dang 30 $ nos dual gang pot didn't smoke.
thanks again, stay tuned, hopefully tomorrow i will have some kind of news.
peace!!

[pinkjimiphoton]

ok, FINALLY got a chance to revisit this last nite.
appears on the last outing i may have smoked a couple more caps. ouch. began replacing the few left from the original kit last nite with fresh 50v 1u electros. gonna swap out the mini 10u's in the oscillator part of the circuit <well, really, just blocking caps, right?> and see if that helps.
audio signal is much clearer than it was, no discernable distortion like it had had.
if i cup my hand over the lamp/ldrs, it will vibe as i block the light. so i am ASSUMING that the phase shifter and audio path are working.
i replaced the bd with a new one, got much better voltages at the oscillator, but the voltages to the lamp driver itself seem kinda weird. discovered tho i could play with the trimmer <and the one i added> to set the voltages across it.
but still no blinky-blinky.
there's nothing in the oscillator circuit thats particularly weird. i'm guessing i may have to replace all the parts, but thats kinda tedious if unnecessary, and i keep thinking its something ridiculously stupid.

the last phase shift stage i'd rebuilt is the only one where i'm  reading the expected 6v across the ldrs; the other stages are all reading around 4.6 v still, which is low. somewhere, something is pulling the vcc low, but i haven't figured it out yet.

i tried disconnecting the voltage to the input pair, as the voltage seems weirdly low still. i got 13v at the junction of the two c resistors, but on the other end of the 1.2m <which actually meters 1.4> i'm getting ABOUT 6 v when disconnected from the side going to q1, but as soon as i recconnect q1, it drops back to about 1.8v.

the voltages on the emitter follower input stage seem insane to me. so i'm thinking replace the 5088's there and socket them.

i DID order another board, just in case. figured by comparison, if i have any messed up traces, that will make it easier to find.

in the midst of a paisly tele today... but will return with voltages later.

thanks for standing by guys.... back soon.

[Ben N]

Don't bogart that Univibe, my friend.

[wavley]

Don't bogart that Univibe, my friend.

Ha! I've been kinda watching this thread because I haven't built a univibe yet and I was really thinking I should make that a priority and I was finally going to chime in with...

So that's what the kids are smoking these days?  I can't keep up with all these new drugs.

[pinkjimiphoton]

smokin univibes is a hell of a drug

i been busy gigging, so have to get back to it. i got distracted building this:

[holm]

Did you ever solve this issue Pinkjimiphoton?

[pinkjimiphoton]

nope,
its been sitting for a couple years waiting me to get to it, along with a couple other things i'll likely never get to

[Ben N]

nope,
its been sitting for a couple years waiting me to get to it, along with a couple other things i'll likely never get to

Ha! Just reorganized my work area with some Ikea utility shelving, so now I have a whole shelf dedicated to those.

[holm]

nope,
its been sitting for a couple years waiting me to get to it, along with a couple other things i'll likely never get to

Oh, sorry to hear that, but you know, I was hoping for a second season...

[pinkjimiphoton]

well, ya know, who knows.....?   

[duck_arse]

.... the shadow?

[pinkjimiphoton]

shit, maybe i should turn it over to one of you guys as a repair gig lol