I found this instrument on internet for sale, having a failure with the selftest showing integrator failure.
I searched on the internet if I could find any reason causing this failure but did not find it as a general problem for this instrument.

I made a bid on it and it was accepted so after some time I had this in front of me.

At start up it indeed showed the selftest failure and temperature at 0 degrees.

I opened the unit and did a visual scan for any lose parts or broken parts, this was unsuccessful.

During the period the instrument was open I suddenly had a moment were it responded like it worked but this did not last very long and failure came back as before.

Looking into the service manual which I found on the internet i decided to dismount the main board and while doing so I found another board below the main board. I also checked this one visual and then I found a bad soldered connector. I did solder the connector again and reassembled the whole unit.
At power up the integrator failure was no longer present and the temperature was showing the room temperature looking very promising

The instrument was working fine again.

A very nice portable spectrum analyzer able also to do VSWR measurements and insertion measurement up to 3 GHz.