Dual 13700-based LFO: Mo' Hotta NOT betta (Shorted OTA?)

Readers--this is a work in progress, you can see the schem and pcb on the one page website here.

========

Hidee Ho! This time I tied to turn a working OTA LFO design (post here) into a dual LFO/small PCB, based on a SOIC SMD LM13700 OTA chip. 

Guess what?  Damn thing doesn't work, the LM13700 keeps heating up, and I have no idea why.

The pain....

 Started as a PCB n' stencil, from the blog's sponsor PCBWAY

I have been using SMD stencils lately, speeds up fabrication

 SPONSOR TIME....

PCBWAY has been instrumental in keeping this blog up off the ground.  

Serene, my totally friendly handler at PCBWAY, told me to tell you: this month they are having specials in addition to their usual great pricing: 

1. Purple Solder Mask: In September, it's free--they won't charge an extra fee for purple cool color PCB's. That's to say, for 10 purple 2-layer 100x100mm PCBs, it's only $5USD, rather than $38.43USD.

2. TPU(FDM) in 3D printing: TPU is good for you! This material starts from $12.45USD, but in September, it's priced from $7.96. The heavier the weight, the bigger the discount, which can be up to 80% off. 

PCB has all sorts of cool services tailored to what we do; you can help this blog immensely by checking PCBWAY out via the link here. Thanks!

USELESS (?) BUILD PHOTOS

Maybe if I look at these pictures long enough I'll find a build fault. but really, it all looks pretty good to me.

Glopped paste and parts pre-bake--looking good I think

As usual, I heated up the plate to 215C, let it sit a minute, then back down to 150C. I am always surprised how well this work and how forgiving the process is. 

Next I soldered in THT parts like trimmers and a few caps:

Finally soldered in the edge connector:

Soldering on the header....

Test time...nope! My power supply is set to 30mA and immediately goes there while the voltages cap out at about 2-3V and the current goes to 30mA on each rail.  Se habla short--the 13700 gets really hot, very quickly. 

Removing it, the short goes away but then (obviously) the LFO's don't work.

So why doesn't this work?

I replaced the LM13700 with a chip from a different vendor (Digikey vs Tayda), same problem; I removed the PNP transistors thinking maybe I had a I-abc issue, nope.  

I spent a couple more evenings troubleshooting, I wished this design was THT (I usually am glad it's not) so I could lift up IC pins. No love.

There was a time I would have kept slamming away on this until fixed, but I have build so many LFO's now that I realized: the hell with it, I can redesign it, pitch it, and/or move on. 

Above all, I have to make sure I am having fun, and more evenings troubleshooting this didn't feel like it'd be that.

I posted to modwiggler to see if those folks had ideas. Maybe they will save my bacon, they have before. if not, this one might be one and done for the dumpster.