This is driving me nuts.

[Mark Hammer]

I am trying to finish up the phase shifter from Craig Anderton (project #21 from EPFM).  A buddy on another forum graciously sent me a handful of CLM6000s and other assorted chips he had bought for making one long long ago, and given up on.  I etched one of the board redraws that JD Sleep has/had on his General Guitar Gadgets site, where he converted things using the now obsolete unobtanium 4739 chip to the more standard 8-pin dual op-amp format.  The etch is fine, with no solder bridges, and all connections seem to go to the right place.

The board is stuffed and wired up.  Since it uses a +/-9v supply, I perfed up a little daughter board to convert +9V from the power supply to the required bipolar supply, using an LT1054.  Disconnected from the board, the daughter board works fine, with a little over 9V coming from the positive and negative outputs.  Connected up the the circuit board, however, I measure about 1/10 of a volt on the positive and negative power lines.  There are NO shorts anywhere, but the 1/4W 33 ohm resistors between the power inputs and the rest of the circuit get crazy hot.  The LT1054 does NOT warm up even a smidgen.

I could see those resistors heating up if the overall circuit was pulling gobs of current, but where is all the voltage going to?  Neither of the two 33R resistors has stopped measuring 33 ohms, although  they do appear discoloured.  I thought "Maybe the 10uf caps intended to smooth power were bad, and removed them both.  Didn't make a difference.  Changed chips, in case they were bad.  No difference.

So:
1) what is drawing so much power/current that it cooks the current limiting resistors and drops the supply voltage? (the EPFM book says the circuit wants +/-15ma, that *should* be within the capabilities of the LT1054)

2) What can I do to remedy the situation?  What change to current-limiting resistances would you suggest?

This could be a very nice little phaser in a nice powder-coated  Hammond trapezoidal enclosure I've had ready for well over a year.  Please put me out of my misery.

[Phend]

Photos please.

[ElectricDruid]

Could it be something to do with the conversion from bipolar power to not-quite-bipolar power?

You've taken the +9V input and used the LT1054 to generate -9V, right? So you've still got a centre ground? (rather than turning it into a unipolar 18V circuit with a Vref=9V, which would also be possible)

[iainpunk]

i had a similar situation in college with a motor control circuit... we found out that due to a silkscreen design mistake, the (+) and (-) markings on the board were flipped over, and the mosfet's body diodes were shunting all the power, and the two 0.22Ω current sense resistors at the input of the power supply stopped working after about 2 hours of trouble shooting. we were having the same symptoms at the power supply as you, really high current and a dropped voltage to about 0.9v, instead of 15v

i also had it with a pedal build way back when i started out. lm358's don't like 9v of reverse voltage on its pins, melting a breadboard and letting the magic smoke out of the epoxy coffin.

cheers

[PRR]

> I measure about 1/10 of a volt on the positive and negative power lines.

I assume this is on the phaser board? Or the power board? Or....

Some of us may not have EPFM memorized; even remember what it is or where it got lost. And you've introduced a mystery voltage converter.

Yeah. No. I love your writing, but this case wants photos and a link to a schematic (Google isn't helping).

[Mark Hammer]

Okay, I looked hard and couldn't find any, but pulling the chips out and touching my DMM probes to the V+ and V- pins shows continuity between them, so there is a short to look for...somewhere.  Time to get back to scraping the board between traces.

But...as requested.

[ElectricDruid]

Nah, it's in the bits of the circuit that *don't* appear on that schematic! How do I know? Murphy's law makes it so, and Murphy is never wrong!!

The power wiring is only given in note form, and your +9/-9 circuit doesn't appear at all, of course. Those are the places where I'd start looking, especially given all the pin numbers for the op-amps are wrong if you've used standard op-amps instead of the weird ones in the original circuit.

[Mark Hammer]

Here's the PCB.  On the right is the original Anderton Layout.  I retouched it to show the actual component values instead of their labels, so I could check over all the components and make sure I had everything in its proper place.  On the left is the GGG redraw.  The top half of it is pretty much identical to the Anderton original, but JD shifted some things around to accommodate the 8-pin chips.  I've looked high and low and can't spot any place where V+ and V- might short out.  To make sure the fault was not on the daughter board, I disconnected that as well.  So, no chips, no extraneous power-supply components, and still I get a reading of zero ohms between the V+ and V- pins anywhere on the board.

[PRR]

> Here's the PCB.

I don't see it?

> the GGG redraw.

Can't find an Anderton-inspired phase shift on General Guitar Gadgets.

> a reading of zero ohms between the V+ and V- pins anywhere on the board.

DEAD zero? Or real low? Numbers?

You have not clearly confirmed polarity reversal, an easy thing to do when working with different chips and sparse (or no) plans.

[Mark Hammer]

I thought I posted it.  Let me try again.



There, that's better.  After using a magnifying headset in tandem with a magnifying glass, under decent lighting, and applying the scraping end of an X-acto blade between any power traces that looked a little close together (followed by brushing like my dentist would want), I now have open circuit between the V+ and V- pins on the sockets.  IC2A appears to be doing what it should, but IC1  may be fried.  In any event, sorry to have led you good folk on a wild goose chase.  My Queen may be dead, but my board may live...tomorrow.  Thanks for your encouragement.