On Wed, 6 Jan 2021 20:37:27 +0000
Fredxx 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. I then checked the power links throughout the board and they were fine.

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I am a bit out of date with electronics since my heydays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

I suggest you measure all the voltages on each pin and come back here
for analysis.

For Info the datasheet:
http://www.bg-electronics.de/datenbl...ise/TBA231.pdf

Although the example test circuit doesn't include the use of Output Lag.
This circuit does:

https://www.vinylengine.com/turntabl...719d&mode=view


Thank you. That focussed the one or two brain cells that I have left.

The DC voltages on the chip with both no external connections (audio oscillator and oscilloscope) were virtually the same:

Pins Voltage Pins Voltage
1 14.3 14 23.6
2 22.5 13 0.43
3 21.0 12 22.9
4 21.1 11 21.0
5 0 10 21.0
6 0 9 0.9-1.6
7 0 8 0.9

Thanks too for the links. I downloaded the spec sheet.

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