t15 not working at all

[kishta]

hi, so i finished my first t15 and got all the resistance and voltage levels correct (i think) but when connecting the mic i get no signal, what i do get is noise that builds up and at level 7 is really loud, a pop sound when swiching levels and a grinding noise when trimming. this goes for a dynamic as well as a condenser { with or without 48+) .....

another weird fact is that my sound card ( rme) shows no input although i can hear it untill that deafning level 7....

please hhheellllpppp!!!!

[tpryan]

What revision of the board do you have?

[kishta]

ahh, 1.3

[kishta]

hello?

[tpryan]

What voltage do you measure at

U1, pin 6?

U2, pin 1?

U2, pin 7?

Let us know what you find.

[kishta]

so , digging in the forums some more i assume i found the right order for the legs numbs' which is notch
1 8
2 7
3 6
4 5
right?
so just to check it again i measured pin 7 on u1 and did get something like 17.90 which i believe is good right?

anyways

u1 pin 6 i get -16.

u2 pin 1 - with the dmm at 20v i get -14.01

u2 pin 7 - with the dmm at 20v i get -4.47

i have to say that doing these tests at first got me zeros and only a few minutes later i got the numbs i posted
dont know if it makes any sense or if i got confused with something...

[kishta]

so , digging in the forums some more i assume i found the right order for the legs numbs' which is notch
1 8
2 7
3 6
4 5
right?
so just to check it again i measured pin 7 on u1 and did get something like 17.90 which i believe is good right?

anyways

u1 pin 6 i get -16.

u2 pin 1 - with the dmm at 20v i get -14.01

u2 pin 7 - with the dmm at 20v i get -4.47

i have to say that doing these tests at first got me zeros and only a few minutes later i got the numbs i posted
dont know if it makes any sense or if i got confused with something...

[kishta]

ok ok!!
going AGAIN over the resistors , i found that i switched r 1,2 with r 24, 25....
so im gonna look for an extra hand to switch those and post my results of course...
sorry.....

[tpryan]

By all means switch the resistors, but it may be too late for U1.

[kishta]

hi again...
so i switched the resistors.
now what should i measure to know if u1 is dead?

please note that on my previous test , u2 got super hot... no smoke or burning smell but still... maybe their both dead?

anyways i ran the same tests as u told me before with the resistors in place..

so:

u1 pin 6 -16.7
u2 pin 1 -3.7
u2 pin 7 11.6

so, let me know whats next and where to order from , please!
thanks

[kishta]

btw- now i get some super distorted sound but at least there is a signal and it sounds like the same note { although distorted without recognition...}

[kishta]

did the board reach a decision?

[tpryan]

It sounds like you have at least one damaged IC. Order replacements from Mouser using the part numbers on the BOM. Don't bother trying to de-solder the old ICs. Snip the leads, remove them one at a time, clear the holes with wick and/or a solder sucker, and solder in the new parts. Be sure to handle the new parts in a static-safe manner and do not overheat the pins.

[kishta]

so i bought sockets and so far have replaced u1 and u2.
the pre is now working...
my next issue is that the trim is working as a full fader and ive done nothing i know of to do that. also the sound is nice but i have a feeling its not the way its supposed to sound.... there is some noise added to it and its a bit pale. sounds similar to the rme pre's.
and ideas?
btw- after reading a bunch about ic's and talking to friends who know more then me , ive learned that the ic's are VERY heat sensitive ...
before i bought the sockets i had heated u1 quite a bit i think {if to compare to what ive been told about dealing with ic's..}
could this be it?

[tpryan]

my next issue is that the trim is working as a full fader and ive done nothing i know of to do that

That's the way it's supposed to work unless you change the resistor at R27.

before i bought the sockets i had heated u1 quite a bit i think {if to compare to what ive been told about dealing with ic's..}
could this be it?

There are many ways to damage semiconductors, over-temp soldering being just one. Search google and youtube for plenty of info on proper handling and soldering of semiconductors.