Second SCA 1272 clone didn't work... Problem found.

My second Seventh Circle N72 has failed to work.

I put the second N72 together the same as the first (which worked fine), except
maybe a bit cleaner (nicer solder joints, etc).

I don't have a current meter so I just plugged it up and tested Q6 like I did with
the first one. I get .469v at Q6 collector regardless of where r39 is.

I then proceeded to test the other transistors. My values are within less than
1 volt on Q1 Q2 and Q3, but at Q4 and Q5 things start to go awry.

Q4 reads 1.145v col, .4v em, and 5.ma at the base. Q5 reads .469v on both the emitter
and collector, and 1.144 on the base.

Of course, Q6 reads .469v on the base too, but I didn't write down the other readings.
Apparently, something is going wrong between the 2 gain stages. I did solder the
conn 3 jumper in place, and I tested to make sure it shorted siccessfully between
pins 1 and 3, but not pin 2.

There are no blatant shorts, and no apparent broken PCB traces, so what could it
be?

Could one or more of the BC184 transistors be bad?

Could I have ruined a cap by keeping heat on it too long? How do I test for this
and where do I start?

Thanks!

Shane

Well, since you have one working board, I?d measure all the dc voltages on it and compare them to the defective board. If they measure the same, put a signal through it and follow it through with a scope.

The clearances on those PCBs are very small... check for solder bridges with a magnifying glass.

If you have an oscilloscope, trace where the signal disappears.

Check for wrong resistor values! or capacitors inserted backwards.

For transistors, Vbe should be around 0.6. And Vce should be not zero (otherwise you have a short, or defective transistor).

Checked over my work doezns of times, compared voltages to my working N72...everything looked good except for an open loop on the output primarys.

Turns out it is in fact a bad output transformer. Hopefull the problem will be solved once a replacement arrives!

Thanks for the suggestions. I love this forum!

Shane