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Hi

I solved the issue. I was not the U2890. I was a broken trace underneath U2965- probably a result of the leaky capacitor and at that time for repair I did not notice the broken trace because it was underneath the IC. It was the connection from U2965 (pin8) to to U2890 (pin 10/9). - (working as an invertor). It was partially working because the inputs were coupling capacitively- that why I could it make worse by touching the IC with my finger. BTW the A5 schematic is totally wrong and does not show that connection ( show to a different gate of U2890). Fortunately I had working A5 board and I could measure the traces..
Maybe there is an update schematic - please let me know.

Bernd

Hey Bernd,

Congrats on the fix. Was your mode of diagnosis purely digital (fingers),
or were there specific signals or test points that pointed you in the right
direction?

Siggi

On Thu, Mar 31, 2022 at 10:34 PM Dr. Bernd Burfeindt via groups.io
<femtocam@...> wrote:

Hi

I solved the issue. I was not the U2890. I was a broken trace underneath
U2965- probably a result of the leaky capacitor and at that time for repair
I did not notice the broken trace because it was underneath the IC. It was
the connection from U2965 (pin8) to to U2890 (pin 10/9). - (working as an
invertor). It was partially working because the inputs were coupling
capacitively- that why I could it make worse by touching the IC with my
finger. BTW the A5 schematic is totally wrong and does not show that
connection ( show to a different gate of U2890). Fortunately I had working
A5 board and I could measure the traces..
Maybe there is an update schematic - please let me know.

Bernd

Siggi


I gave up at some point to understand the theory of operation for the readout function - too complicated. So initially is it was the finger- afterwards I try to understand the circuit and I concluded that probably the input signal was to low - as I could influence a digital signal with my finger. Then i measured the level and confirmed that the inputs were practically zero, comparing this with a the 2nd scope made it really clear.
As I mentioned the schematic for the digital part are wrong- so I had to reverse engineer that schematic by looking at the "good scope" I am wondering If there is a new revision of the schematic. My scope has S/N higher than 50K which is listed in the standard service manual.

Bernd