Tremulus Lune fades out....

[BDuguay]

I have a Tremulus Lune that will work fine sometimes and other times, after less than a minute, the effect and signal both fade until there's nothing. By pass works fine as does the LFO LED indicator. I've searched but found nothing. I need help please.
Thanks,
B.

[foxfire]

maybe a bad solder joint somewhere or something overheating?

[BDuguay]

Solder joints are good and no heat problems. Anything else?

[darron]

if you can still see the rate display LED flashing properly then that at least eliminates a large bulk of the circuit (:

that would mean the LFO is working, and i would suppose it's safe to say that the other LED and the LDR are working. The only things that are left are a couple coupling capacitors, DC filtering capacitors, and the opamp chip.

if the LED by the LDR was dim then the LDR would increase very highly in resistance and practically mute the signal. maybe next time it does it try putting a jumper over the two LDR legs. this should make the circuit louder and not have the tremolo effect. if that does nothing then you can safely disregard the LFO part of the circuit completely. the main things to check then would be the opamp, the trimpot and other pots, and the capacitors. you eliminate the coupling capacitors by putting a jumper over those too. that simple elimination covers most of the circuit. failing all that run an ohmmeter to check good continuity everywhere in the signal path from the input to output. it could be something really silly like a component shorting by the jack or power socket.

[BDuguay]

Okay, so the LDR jumper did nothing so I'll check the coupling caps next. Now, this Lune is the Tonepad version so which exactly are the coupling caps?

[darron]

i doubt it's the coupling caps, but it's a very quick thing to be able to check. on the tonepad schematic they are the first thing the signal goes through and the last, so bottom left and right. the 1uf caps.

are you getting proper 9 volts at the opamp and 4.5 volts going to pins 3 and 5 (Vb)? to check, press one end of your voltmeter to ground somewhere and the other end (positive) to pins 8 (aobut 9v), 3 and 5 (about 4.5v).



here's the schematic for future reference:
http://www.tonepad.com/getFileInfo.asp?id=84


if you can't find the solution, then follow this proceedure:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[BDuguay]

I thought those were the coupling caps but I'm not afraid to look stupid by asking
Now, this pedal was built by somebody else and all I've done so faris tidy things up. The coupling caps he chose are NP electrolytics. Do you suppose somthing could be wrong with these?
Thanks for the opamp voltages, I'll check them now......

[BDuguay]

The voltages check out but now when engaged it doesn't pass signal at all. The LFO LED still works. I'm going to go over each solder joint again but in the meantime, does anyone have any other suggestions?
Thanks,
B.

[darron]

if the LFO is working properly, and you have already determined that the LED/LDR is working, and bypassing the caps hasn't done anything, then the only thing left is the opamp. chuck anything with the same pinout in there (very common dual opamp, 4558 style). i'd be more inclined though to check for any shorts somewhere to ground or a place where the signal is broken. pull out the multimeter and check for continuity of the signal from one jack to the other to look for a break or short to ground. does the opamp pass signal if you crank the amp up, and strum really loud? dead opamps or opamps without power will still usually pass a very, very tiny signal that's very gated and farty.



try making a short between pin 2 of the opamp to pin 7. be careful about it though. it's a very small path for the signal to travel from the jack through the very few components which are not associated with the LFO. for example, don't even bother with checking out the pots as they are of no concern to the signal.

even sometimes you can be looking for ages and see the ONE TINY little fine strand that shorts itself from the tip on the audio socket to ground the can get bumped about, but that doesn't as much explain fading signals.


i'd chuck in another opamp just to test, you can always put the original back in if you liked it.


good luck

[BDuguay]

Which of the 2 opamps are you suggesting I should swap out? I'll need to remove both of them anyway because currently, they are  not socketed.
Thanks for all of your help Darron!
B.

[darron]

just IC1. IC2 is for the LFO and obviously works. try shorting those pins first though, if shorting those pins doesn't let a bit of signal through then look at places other than the opamp. but there's not much left to eliminiate.

seriously, get the multimeter out and check continuity and resistance for the signal from right where it comes in, the places in between, to right where it comes out. it's not much to cover. look for shorts to ground also.

[BDuguay]

I removed IC2 ,installed sockets, then popped in a new chip and ...... IT'S ALIVE!!!
Thanks for all of your help Darron.
B.

[darron]

sweet