Your tuner may or may not be a door stop at this time, there are a some simple tests that can be done and it might be a simple problem.
Since it makes noise in both the AM and FM modes that would make it appear that both IF chains and detectors are working.
On thing that is common between the AM and FM sections are the varactor tuning diode voltage. Not only does it drive the diodes in the RF front, it drives the diodes in the local oscillators. These diodes take the place of the mechanical tuning capacitor in an analog tuner.
The circuit that drives these diodes is just a handful transistors.
The output of which has a 2.2 microfarad capacitor (C501). If it is shorted or electrically leaky , no tuner. There is an IC (IC 501) that drives these transistors and this IC is driven by IC 502, the tuner control IC.
I would start by measuring the voltage on C501. It should change as the tuner's frequency is changed. If no voltage there or it does not change I would check the output of IC 502 (pin 7), the voltage there should also change as the tuner frequency changes.
This may not be the issue, but it is fairly simple trouble shooting and the AM circuit is fairly simple. It sends it detected audio to the same place the detected FM audio goes and there is noise output on both AM and FM.
Of course start by making sure all of the power supply voltages are present and correct.
After that a digital oscilloscope would be handy to look at the serial data and see if IC 502 is getting the correct data and clock pulses.
This tuner is not that hard to trouble shoot if a person has had experience with both RF and digital electronics.
I have not checked on parts availability.
The OP has indicated that the display works, channel scan works, mute works, AM/FM switching works. This is an indication that the tuner control IC (IC502) is possibly working okay. This is the IC that drives the PLL IC (IC501) that drive the handful of transistor that drive the varactor RF front end diodes and the local oscillator varactor diodes.
Again, one would need a way to look at the serial data lines, but that is not a big deal for someone that has a digital oscilloscope.