I sometime have the feeling that there is something wrong with my MKS-80 Rev 4.

I attached two files. MP3 and a picture of the same sample analyzed by Cubase pitch detection.

You here 3 notes. All C5. Portamento is set to 0.

At the beginning of the first note the pitch goes up. At the beginning of the second note it's not so strong anymore. The third seems ok.

This kind of artifact is stronger on higher pitch. From C3 down it's neglectable.

I don't know, but is this normal or is something wrong with my Synth. It's annoying only on Piano or Harp kind of sounds.

Does no one have a MKS-80 rev 4?

You can't see pitch go up in a waveform, so I'm not sure how helpful your picture is.
Your audio file sounded OK to me. If it's something changing pitch it is very, very subtle.
Without being in your room, or seeing what else is programmed in the sound it's very difficult to help.
There is pitch envelope, there's modulation, there's oscillator sync. Any number of knobs or sliders could be effecting the pure pitch of the patch.
As i said, I couldn't really hear it. Do you have a patch where it is much more obvious?

Edit: At a higher volume I can hear the notes getting less bright, from first to third. Again, there's lot's of MKS80 functions that could be effecting this.
It's an old synth and the imperfections are part of the beauty and soul of old synths. Your audio clip doesn't sound too odd to me.

Gotta be honest; I don't really hear it on my laptop speakers playing 5-6 times in a row and straining.

bin it, that thing belongs in a museum. then get a deepmind12 they look good

it shows cubase pitch detection as well, as noted

to the OP, if you want "perfect" use plugins

I don't hear it. MKS-80 is known for not having the most stable VCO's. There is a lot of circuitry packed in such a small space, so heat can be an issue. Like Chrisso, I did notice the change in brightness, but that was fairly subtle.

I recapped mine and it greatly improved the tuning stability, but mine had leaking capacitors, so it was bad. There were other issues.