I guess I'm getting worse at building these kits....problems

[jlearman]

with both my T15's

The first one: I get nothing but this hiddeous screatching sound. If you want to listen to it I uploaded a clip here:

http://webpages.charter.net/jlearman/T15_ch1.m4a

The voltages at the +/- 20 v pads are approx 17.94v and -17.89v. I noticed that u3 is getting very hot....not sure what else to check.


The 2nd unit passes audio but has this constant noise in the background. Clip here:

ttp://webpages.charter.net/jlearman/T15_ch2.m4a

Everything on this unit looks good..nothing getting to hot, voltages look good at the +/- 20v spots.

Thanks in advance for the help tim...sorry to keep doing this to you.

-Joe

[tpryan]

Module 1:

All ICs and electrolytic caps installed the right way round?


Module 2:

Output pins 2 and 3 must be properly terminated. If you're driving an unbalanced input, make sure pin 3 is grounded.

[jlearman]

yep, IC's and caps are all right way around

[tpryan]

Module 1:

Are D5 - D8 installed correctly?
What is the voltage at U3 pins 3, 4, 1, and 8?

[jlearman]

D5 - D8 are definitely installed correctly. I'm not sure what pin is what, so starting from the corner with the dot, and going down the long side of the chip, then jumping diagonally to the other side and going down, the voltages are as follows:

-13.16 v
-11.37 v
4.0 mv
-16.69 v
-0.4 v
17.12 v
17.93 v
-17.9 v

[tpryan]

Doesn't look good. How about U4, pins 3 and 6? You can see the pinout here: http://focus.ti.com/lit/ds/symlink/opa604.pdf BTW, the numbering scheme is the same for all other 8 pin DIP packages as well.

[jlearman]

-60 mV at pin 3 and -45 mV at pin 6. I couldn't get a consistent reading though...it fluctuated a lot. I'm putting the red lead of my meter on the point in question, and the black end on the PGND. is that correct?

[tpryan]

So you have -45mV at U4, pin 6 but -16.69V at U3, pin 4? That can't be right.

[jlearman]

Hi Tim,

Can I just send this into you? I just don't have the time to trouble shoot this thing...

Thanks,
Joe

[tpryan]

Send an e-mail to rma@seventhcircleaudio.com if you want to send it in.