Having problem with La Rata build

Started by dpresley58, August 03, 2010, 10:08:53 PM

Previous topic - Next topic

dpresley58

Hi, all.

Schem is La Rata.
Board generated using photosensitive process and CAD-generated artwork. Artwork has been proven with two previous successful builds.
No parts substitutions

My cousin and I were building a couple for ourselves this weekend. Upon completion, they both had the same problems - Little or no signal on the output of the opamp. Voltage divider was working on both, and all diodes read about 0.5 across them. Opamps checked with this circuit (http://tangentsoft.net/elec/opamp-tester.html) and verified according to it.

FET (2N5458) G 0.00  S 1.72  D 9.35
Pins on opamp 1) 8.82  2) 9.36  3) 8.67  4) 0.0  5) 0.0  6) 0.53  7) 9.35  8) 0.02

I'm only giving the one set of readings because both were so close. THEN, we decided to build a third one jointly. Another board was burned, we both checked the results with an Xacto, measured all the parts before stuffing them, checked and re-checked the solder work. The third board had the same problem as the first two.

Of the parts, I wasn't sure about the 100uf electrocap because it took a while to register a value. The 30pf and 100pf coming off the feedback loop were 45pf and about 150pf respectively. What am I missing, and what are the odds of three boards having the exact same symptoms?

Any help would be appreciated on this. Thanks in advance.
Little time to do it right. Always time to do it over.

brett

Hi
pins 2 and 3 should be biased to approx Vs/2, but ther's not.  That's why the output (pin 6) is stuck low (the inverting input is higher than the +).
cheers
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)