On 06/01/2021 20:24, Martin Brown wrote:
On 06/01/2021 20:16, pinnerite wrote:
Ten years ago I bult a low-noise pre-amp based on a 1970's article in
Elektor magazine.

It used a TBA231 dual op-amp IC.

It didn't work but I did not have time to test all the copper runs
etc before I wa over-whelmed with 'work'.

This week I took it out and started fault-finding.There was one open
connection, poorly soldered.Â* I then checked the power links
throughout the board and they were fine.

The chances of an Elektor design of that era working as drawn were
marginally better than those in Wireless World but not by much. I
suggest comparing what you have got against one of the old application
notes for that chip in the hope that you can spot what is wrong with it.

Next i connected in a little waveform generator to the input and one
of those timy LCD screened chinese oscilloscopes to the output.
Nothing.

So with no shortcircuits, I concluded that the capacitors were OK
whch only leaves the IC.

I do not have another TBA231 or equyivalent but have no idea how to
test the chip.

I am a bit out of date with electronics since my heydays

So any suggestions will be welcome.

Is it drawing any current? Is the output more or less mid way between
the two power supplies or stuck against one of the rails.

There are much nicer low noise preamp chips available now.

That was my thought too.