Bust Electric Mistress

[PacoPicoPiedra]

Hi all,
I've got a deluxe electric mistress, not sure when from but it has the built in power supply so I'm guessing it's one of the 70's ones. Basically, whenever you move the trimpot for the clock rate at all from where it is (fully clockwise component side of the board), you just get a big wall of white noise which gets flanged itself. This isn't much fun really as you only get a pretty weak effect when it's in this position, sounds more like a phaser, and I'm pretty sure you should be able to adjust it being as I've heard of people swapping it for an external pot because of the range of sounds it gives. It's been to a tech once, the guy basically just gave it back as it was  , so I'm thinking I've gotta sort this one out myself.

Anyway-(Bad) Pics:








And a sound clip:
http://www.sendspace.com/file/zav0ve
I'm just turning the pot from clockwise to anti-clockwise with an open jack in the input

Help much appreciated!

[PacoPicoPiedra]

bump.

[PacoPicoPiedra]

come on, no one have any ideas? doesn't theehman know all about this stuff?

[GREEN FUZ]

Sounds cool!


Can`t really help you though. "Could be" a busted op-amp. My advice is, first of all, check for any obviously blown or damaged components, but I`m sure you`ve already done that. Secondly, make an audio probe and try and trace where the sound starts to fail.

[soundcollage]

Try replacing the trimmers with multi-turn ones. They are easier to dial in and less likely to drastically drift with vibration.

[StephenGiles]

Perhaps be a little less aggressive in your post, some of us do have a life outside this forum

If you say that the white noise is being flanged, then it sounds as if the BBD is OK and probably the LFO and clock ICs  - LM324/LM311/CD4013 are OK too. I would check the voltages on pins 1 & 2 of the CD4013 which should be around 7v on each. If one is much lower then it could be either the 311 or the 4013. If that is OK, I would change the 741 and the 4558 in the audio route, remember that the 4558 is a dual opamp and the 741 is a single opamp.

Let us know what happens.

Buenas

[PacoPicoPiedra]

sorry man, didn't mean to be aggressive, you know how it is when something's not working, 
can't say I really know anything about chips or op amps (I just about know what one is) but I can follow instructions at least. I would guess you're right about the lfo and the bbd being ok as everything functions fine except when I turn that one trimpot up. anyway i'll check those voltages and get back to you tomorrow,

Regards

[PacoPicoPiedra]

ok, assuming I'm reading the right pins (bottom left 2 with the notch on the left) i get about 7.2v on pin 1 and 7.1v on pin 2, if i turn the trimmer up at all these both drop to about 0.1v

[PacoPicoPiedra]

checked the SAD1024 as well , voltages on the 1st 4 pins are 14v, 7v, 14v, 7v but pin 2 drops to 0 if i turn up the trim at all, others stay the same. don't know if that's of any significance, really need someone to guide me thru this, I don't have a clue what i'm doing 

ps.
got 14v on the input of the 741 if i remember rightly, that doesnt change so i'm guessing it's as it should be

[PacoPicoPiedra]

don't mean to keep bumping but I need the help, anything else to check Stephen?

[PacoPicoPiedra]

just to let ye know-success!

a bit of deduction pointed me in the direction of the trimmer itself, and sure enough desoldered it and theres a dirty great crack across the track, the one leg fell straight off. replaced it with a 100k pot which i'm about to drill the case for and i've got all my lovely soundz back

[StephenGiles]

Well done!