I still like and use casettes too ;-)
I fix old radios asa a side hobby, i not an expert in it.. but I like to struggle I guess and ive had some sucesses,
I only work on old tube radios though, pre transistor era. pre 1965 era.
anyway Ill look for the schematic first if I look into one. most old radios are covered..
here are two links but they likely wont have car manual or anything that new.
if and when you obtain the correct schematic it will have info on how to perform the alignment as well as a circuit diagram and a parts list.
these sites have schematics for older radios and bama is a
boatanchors" shematic archive , ham readios and such mainly.
shttps://bama.edebris.com/
and this one
https://www.nostalgiaair.org/ it has ost of the old radios I tend to work on.
normally the schematic will state what frquency the IF capacitors run at. often in typical radios it is 455 but on a car radio, well the IF cans to work at the defined frequency. If you dont have a grip on what you are doing leave the screws alone.
what this does is peaks the frequency they use to "trap" the station you select and if that is off, the radio wil be weak. basicaly you inject a frequency and listen tot he speaker and find the lioudest adjustment spot by tweaking them slightly until happy.
the IF cans can have a problem, it is called "silver migration " or also "silver mica disease" that can make it crackly and unusable.
next the ( radio) bands need to be adjusted, two adjustments work in conjunction one is the bandspread or the distance between lets say 600 and the top of the dial maybe 1200 or1400 so. if that is out the radio will tune into 600 but at the top of the dial may be incorrect..
the other is to inject a kown signal I use a signal generator, you can improvise with a downloaded oscilloscope or other ways.. then you inject a frequency and tweak the adjustments to check that it tunes 600 at 600 on the dial and 1200 at the 1200 mark, or somethign similar. if that is off the stations wont be in the correct lace on the dial. i dont understand digital tuners< ilke the simplicity of no numbers. so that adds complexity.
a car radio might have an antenna trimmer pot, this may help adjust for a paricular antenna that could be in a schematic for the radio.
how do you get the porsch radio schematic, was it freely published?
I wont generally work on transistors because the parts get a bit small and my eyes dont cooperate so well and I just basically become lost.. but anyone that works on transistor radios can likely give it a little tune up.
often radios will work , well sort of but if they aren't adjusted right then they may not perform very well. they loose selectivity.
FM is yet another complexity.
some of the "beitmans" schematics fo cover car radios, this link to internet archives shows a set , but only up to 69 maybe there were later ones.
https://archive.org/details/BeitmansMostNeededRadioDiagrams/1926-38/
if you have not so much familiarity but wish to try or get help if you can download the correct schematic its helpful. provide that to your bench tech if you can.
if you haphazardly adjust things, good luck with doing that you will inevitably screw it up. someone with a little experiance might be able to help some, without a schematic. but dont try that if you don't understand what the adjustments all do.
in general the old school tube radios I work on will hum if they play at all , Ill replace capacitors and test between each. usually that brightens it up and removes hum, and then do the alignment per instriuctions alignment can make a huge difference if it is off.. now in a transitor radio it is possibly fine and may not need adjustment at all, so just test it..
I have the same issue in my volvo tape deck radio, no display, It was very hard to get out so Im leaving it blind, I dont need to see the digits anyway. i just hit "scan" and find a station I like.
what you describe is a ribbon cable a flat piece of mylar with traces which are wires, they ofted clip ( or slide with friction) into a connector, if you take it apart just try reseating it. it may have pulled loose a little during assembly.
sorry I dotn knwo much about car radios but its a superhetrodyne and not that diferent from most other radios. on AM, but FM is more complex.
one approach if you ave it apart just replace the electrolytic capacitors with the same value. they do age out. watch the polarity ! the line on the tin can is negative so take pics dont install them backwards. the electolytics are polarity sensitive, other capacitors, not so much but they may be ok in a radio that new, same for resistors.
I'd check any resistors. look up the value by the color bands. then mesure with an ohmmeter to find the resistance. they tend to drift towards being less conductive higher or more resistance.
it is possible to have a different path from the two ends of the resistor so in general you can lift one leg but there can be no other alternate electrical path that INCREASES the resistance. any alternate path can in theory lower resistance. lifting a leg omits that confusion.
if you measure them in place look for any ones that might offer more resistance or a higehr value than what is specified. in old radios Il often find bad ones maybe one is completely open. stuff I work on is older bigger and generally higher current. transistor sets are more electrically efficient than old tube radios.
the resistor bands, look it up, there are easy calculators online.
if t works well enough, other than the ribbon cable then just enjoy it. If you send it to a guy that does electronic bench work he can likely align it and check this stuff . rebuilding it can make it a lot more sesitive and work better ,if it does need work.
tape decks may have rubber bands , capstan drive rollers, you can clean them maybe the drive bands can be replaced. Ive saved many decks from earlier years and I often find they cease to work at all , maybe broken drive bands? you can order a general selection and hope to get the right ones.
if there is an antenna trimer on the back of the set this may help and you could probably jus tnote where it is and adjust it a little in the car, connected to your antenna.
with Am in general an antenna shoud be loing and away from interference, in FM I htink the standard length is 33 inches you could check that spec. I might be a little off but with FM the length can be optimized. the antanee trimmer , if present, may help with that