auditronics preamp resistor blown

[steenamaroo]

hi all!

i'm new and i've signed up here cos it looks like a great site, and i'm in a spot of trouble.

i've recently racked up two auditronics preamps, one of which went beautifully, but the other has gone wrong!

i made a mistake when wiring in an led meter that shares my 15v supply and as a result, blew out a resistor

(r34 in schematic below)
http://avensonaudio.com/tech/auditro...onics_110b.pdf


i replaced the resistor with the same, and as soon as i powered on it smoked again.

sadly it was a strain on my knowledge even racking the working unit, so trouble shooting is a bit beyond me,


if any one would be able to point me in the right direction for testing, or even be able to suggest what would cause this problem, i'd really appreciate it.


just so you know, the working unit and the non working unit have been wired up identically, and the testing was carried out with the same psu etc..



thanks in advance all!!

[dhaen]

Which resistor?
Have you removed the "additions"? If not, restore it to normal until the problem is sorted.
Make a careful visual inspection to see if there is any blob or spider of solder that could cause a short circuit. (They can land a long way from the working zone).
Are connectors correctly located and oriented?

Post a picture!

[steenamaroo]

hi there... and thanks for replying


it's r34 in the schematic...it's the 10omh at the -15v terminal.


i have removed all extras (output card and led meter) to isolate the problem to the preamp.

i've inspected the the working and non working units side by side, and can spot no difference between the two...


my soldering has been really neat and careful, and there are no blobs that i can see.



the unit did work fine until i accidentally used the -15 supply in place of the 0v when adding an led meter....this is when the resistor popped.



with the unit rewired in a known to work fashion, replacement resistors keep blowing on power on.

by having the working unit for comparison, i know that everything is wired up correctly, so the issue isn't there..

[aparatusonitus]

Most likely you have fried IC1 (NE5534) opamp, replace it along with R29/33/34/35, but first solder DIP8 socket for NE5534 (without opamp) so you can check voltages prior opamp installation.

[steenamaroo]

hi there, and thanks!

checked out all those resistors and they seem fine. i even compared with readings from the working card just to be sure.....



as far as the opamp, even without the opamp installed, i'm still burning the problematic resistor

[steenamaroo]

would there be any logic in replacing c9?

this was the first thing i thought of when the resister kept smoking, but then i am a complete noob

[steenamaroo]

hi again.

sorry to flood here, but i have an update.

i took the three ic's from the troublesome card and put them in the working card.


the working unit still worked with no problem, so i think i can rule out damage to the ic's.


i have ordered a load of 10ohm resistors and some 10uf 25v tant caps.

plan is to replace all of the caps and resistors just to be safe, and test again, but short of that, are there any more suggestions???


thanks!