18V Electric Mistress - no sound - basic troubleshooting guidelines?

[goldenhound]

I know this is for DIY stuff, but I figured there must be some accomplished builders that can help me.

30+ years ago, I put my EH Elec Mistress in a suitcase, and 3 years later I removed it and it didn't work.  A new set of 9v batteries, and nothing.   The audio passed thru OK, but when the switch directed the guitar signal thru the circuit, there was no output. 

I have rather fundamental skills with soldering and circuit tracing.  I checked for unsoldered wires, and there was one, I think.  I found where it broke from and resoldered it.  No joy.  I replaced the SAD1024 bucket-brigade chip.  Nothing.

I found an article on building an audio probe and built it hoping I could find out where the signal stopped, and start replacing components.  The signal from the guitar in jack stopped at a resistor early on in the circuit .  I checked the resistance and it was to spec, but I couldn't get the signal to go past that point.

How does one go about trying to fix this pedal?

[theehman]

Make sure you're getting 12-13vdc to the ICs.

[Tony Forestiere]

The 18 volt version has two trimmers. One sets the voltage regulated by the 741 and 2N5037 (collector out) to supply 12 volts to the circuit. (lower left side of the schematic). Once this is confirmed, slowly tweak the other (upper right side near the BBD) until you get flanging. Mark the original positions first.

Good luck.

[theehman]

The 18 volt version has two trimmers. One sets the voltage regulated by the 741 and 2N5037 (collector out) to supply 12 volts to the circuit. (lower left side of the schematic). Once this is confirmed, slowly tweak the other (upper right side near the BBD) until you get flanging. Mark the original positions first.

Good luck.

Actually, one biases the BBD and the other sets the maximum feedback.  They have nothing to do with the voltage.

[goldenhound]

Thanks for the "next steps".  I'll try to find the chip data sheets and check the voltage.  Thanks for posting the schematic.  There are several out there and I believe this is one of the ones that I looked at.  Mine was purchased new in 1978.

I've since read the "Debugging Page".  I'll see what I can find out about the rest of it and post what I find.

Regards and THANKS!
Rob

[Eduard_Solderingironhands]

Hello goldenhound ,

Most of the information needed can be found on The Mistress Mystery Page.
Here is the troubleshooting sequence
and here you find reference voltages and waveforms.

Best wishes

Ralf

[goldenhound]

OK - I'm totally embarrassed to be asking this question, but I'm finding no luck in checking the pins for voltage.  I've come to the conclusion that I'm not finding the ground.  Where should I attach the ground of my DMM to the Electric Mistress?  Depending on what lug of the input jack I attach it to, I either get no voltage, or 18v on virtually everything.  Is that possible, or have I blown the voltage regulator section (or does that have anything to do with it?).

[petemoore]

  The circuit and box get ground from the amplifier cable sleeve.
   You might need a plug snerted into the input jack to turn the ground 'on'..if there's a power defeat switch formed by the plug being in/out of the jack.

[tubelectron]

Hello goldenhound ,

Most of the information needed can be found on The Mistress Mystery Page.
Here is the troubleshooting sequence
and here you find reference voltages and waveforms.

Best wishes

Ralf

Many Thanks Ralf for your accurate informations ! I also have a mint condition untouched EH EMF 18V version which unfortunately doesn't flanges, and let hear a dry signal both when engaged and unengaged. So I will dig your tips...

Posted by: Tony Forestiere 

The 18 volt version has two trimmers. One sets the voltage regulated by the 741 and 2N5037 (collector out) to supply 12 volts to the circuit. (lower left side of the schematic). Once this is confirmed, slowly tweak the other (upper right side near the BBD) until you get flanging. Mark the original positions first.

Good luck

Thanks Tony too - I'll check it...

A+!

[StephenGiles]

Clock pins should be 1/2 of V+

[goldenhound]

Hi Ralf,

Thanks very much for the links to your pages.  I actually discovered your pages and began using them even before I posted here!     Thank you for your exhaustive details on the types of Electric Mistresses. 

According to your page, I have a Version 2.  I am following your troubleshooting steps, but unfortunately, I don't own, nor do I know how to operate an oscilloscope.  For me, this has become a quest over the years.  This is the 3rd time I've attempted to resurrect this pedal, and I learn something new each time.  The last time was back in 2007.

Thanks again!
Rob

[theehman]

Hi Ralf,

Thanks very much for the links to your pages.  I actually discovered your pages and began using them even before I posted here!     Thank you for your exhaustive details on the types of Electric Mistresses. 

According to your page, I have a Version 2.  I am following your troubleshooting steps, but unfortunately, I don't own, nor do I know how to operate an oscilloscope.  For me, this has become a quest over the years.  This is the 3rd time I've attempted to resurrect this pedal, and I learn something new each time.  The last time was back in 2007.

Thanks again!
Rob

You don't need a scope.  I've repaired/aligned a lot of them over the years with a multimeter and a signal tracer.

[goldenhound]

Hi Pete!

Thanks for your information regarding how to find the ground.  As you've said, it takes a mono plug inserted into the input jack to send power thru the circuit.   You mentioned that "ground" is supplied from the amplifier cable sleeve.  I'm a little dense and need stuff spelled out to me.  Does that mean I should be checking my circuit while its plugged into a running amplifier?  I'll give it a try and see if that makes a difference.

Thanks too, to Stephen for his information about V and the clock pins!

[theehman]

just put the black lead of your meter through one of the screw holes in the chassis.  That's the ground.

[goldenhound]

Thanks for your posts Ron.  They've been helpful and informative.  I just posted regarding the fx ground.  If you have a chance to read it, does it make sense?  Seems so simple yet, with a portable, battery-driven effect I can't even start to find the problem if I can't find ground.

[theehman]

You'll need a cable plugged into the input jack to turn the pedal on but you don't need it connected to a guitar or amp if you're just checking voltages.

The ground isn't supplied by the sleeve of the plug but the sleeve is used to connect the battery negative to ground to complete the circuit.

[goldenhound]

Well, I tried putting the black lead from the DMM into a couple of the screw holes on the PCB and on the box itself, but I'm not finding voltage anywhere.  Also, I noticed that the batteries that I'm using were very warm - Very warm.  Kind of sounds like I've got some kind of short somewhere.

[theehman]

sounds about right.  Could you post a pic of your circuit board? Trace side is fine.

[goldenhound]

Hi Ron,

I tried to upload a couple of images, but copy&paste doesn't work, and there doesn't seem to be an option to upload an image.  I see an icon that says, "insert image" but it just produces html img brackets.  How do I upload them?  Additionally, I apologize in advance for the poor image quality.  I don't even know if they'd be worth it.  This is from my phone's camera.  My regular camera is inaccessible at this point.  If you want send me an anchor email to Goldenhound104@gmail.com, you may, and I'll respond with those images.

Thanks,
Rob