Mutron II Phaser- power issue?

[the3secondrule]

Bit of a weird issue with my mutron II, built as per the build docs here:
http://www.madbeanpedals.com/forum/index.php?topic=6749.0

About 50% of the time, when powering up it will pass no signal.
I've popped the back off to see what happens, and when it is passing no audio, the LFO led remains brightly lit (brighter than when oscillating). Sometimes plugging and unplugging the power will help, often it wont. any idea's?

I got voltages from IC7 to start with (I used LT1054 with pin 1 lifted)
first the voltages while latched up + passing no audio:
pin 1 nc
9.57
0
33.3mv
0.7v
4.4v
200mv
9.59

and working voltages:
pin1 nc
5.16
0
-4.14
-9
2.5
1.4
9.59

This is an AWESOME phaser and would be permanently on my board if I could rely on it to work every time.

Any ideas, thoughts, feelings or suggestions?

Cheers,

J

[Scruffie]

Couple of ideas, someone might have a better one but...

How many mA does the supply you're using give out? I'd go with a minimum of 200mA

What kind of LED are you using?

What Op-Amps are you using?

Just wondering if it's a current supply issue causing the LT1054 to latch up, a 30mA high bright LED with NE5532s for example would be eating a lot of current.

[the3secondrule]

Thanks Scruffie,

tried a few different supplies - one putting out ~200mA, and the other 1.6A, as well as running it off my BBE supacharger, same behavior with all.

LED is a diffused yellow 5mm, from smallbear I think, and OA's are tl072s.

J

[Scruffie]

TL072 in the LFO too?

[the3secondrule]

TL072 in the LFO too?

yup, as per the build doc. Worth swapping out for a tl062 perhaps?

[Scruffie]

I'd say so, or a 1458 etc.

[the3secondrule]

really wishing i'd socketed that chip right now 

I'll give it a try, cheers

[the3secondrule]

Dammit, I have everything except for a tl062 or 1458.

I've tried a jrc 4558, 4559, lf353, tl022 - no joy.

looks like i'll need to order some 062/1458's anyway - are there any other OA's I could/should order to try out?

J

[jimilee]

Could it be something as simple as stomp wiring? Tried reflowing? Just a stab in the dark from past experiences.

[the3secondrule]

I'm pretty confident it's not the stomp wiring - purely because I can't see how the stompswitch would effect the the LT1054 voltages.

not that i've never messed up wiring a 3pdt 

[jimilee]

Right! this is odd for sure. The intermittent thing makes it more strange.

[Scruffie]

Dammit, I have everything except for a tl062 or 1458.

I've tried a jrc 4558, 4559, lf353, tl022 - no joy.

looks like i'll need to order some 062/1458's anyway - are there any other OA's I could/should order to try out?

J

Hmm, TL022s are normally good for LFOs I think off the top of my head... might not be the problem.

358s are good btw though just to mention.

I wonder if it might be the LED driver transistor causing latch up then... what did you use there and is it definitely orientated correctly?

Also check electrolytic orientation in the LT1054 section just to rule that out.

Doesn't sound like it's being caused by the audio path i'd hazard a guess so i'd dig round the LFO and power mainly.

Guess it could be a bad solder joint?

[the3secondrule]

Bumping this again - my tl062's arrived, and still no joy, it's only working about half the time. forgot to order some 1458's though

for the transistor I used the 2n4401 specified on the build doc. will double check the orientation, and the caps around the charge pump, and give it a once over for cold solder joints. maybe socket the transistor and audition a few other types?

interestingly enough though, I have built a second board that is exhibiting the same symptoms...

Hmm, TL022s are normally good for LFOs I think off the top of my head... might not be the problem.

358s are good btw though just to mention.

I wonder if it might be the LED driver transistor causing latch up then... what did you use there and is it definitely orientated correctly?

Also check electrolytic orientation in the LT1054 section just to rule that out.

Doesn't sound like it's being caused by the audio path i'd hazard a guess so i'd dig round the LFO and power mainly.

Guess it could be a bad solder joint?

[the3secondrule]

On a hunch, I replaced c18, the 10uf of the -9v rail, with a 100uf.

Voila, it lives!

[Scruffie]

On a hunch, I replaced c18, the 10uf of the -9v rail, with a 100uf.

Voila, it lives!

Nicely done! Bad parts can be a right pain to catch.