I am refurbing a car stereo from an early-90s Volvo (stereo model HD-603) - plus replacing the cassette circuit with Bluetooth and Aux In. But this question is not about this modding per se.
The stereo itself, being 30-years-old, initially was failing due to the main input cap leaking its guts, and despite now working after that repair, there are a number of (quite a lot of) electrolytic caps on the board, and of all the ones I've pulled and tested off the board, they are drifting off and mostly high in ESR.
So - before reinstalling the stereo, I will replace the electrolytic caps with exact like-for-like, only LESR, plus there are several sub-1uF electrolytic caps which I will replace with polyesters of the same values.
My question is - might these new caps (despite being all exactly the same uF values as the originals) potentially affect biasing or possibly introduce new issues? (If so I won't do it!) (And I am a capable solderer, and won't put them in wrong!)
The car stereo board has 3 test points and 4 pots - though I don't have a schematic or much info about this board. I don't know if these pots are for bias adjustment or levels.
Also - I should add that this stereo unit appears to only output to an external power amp buried elsewhere in the dashboard, and, doesn't seem to have a 'power amp' stage itself, with larger transistors/fets and output caps. So I guess the matter of DC offset at the speakers isn't an issue.
Thanks for looking at this.