Symptoms of the patient: 8508A gone bonkers, fails to zero on resistance ranges (error during input zero 2004)
Being switched off for 30 minutes and it fails to start up properly, one of the lcd displays remains black and entire unit is nonresponsive.
There is a signs of earlier butchered capacitor replacement on the power supply board, blue 50v 470uF electrolytics have been replaced before. Power supply seem to run rather warm (8508A doesn't have any sort of cooling fan.)
On closer inspection the blue 50v 470uF caps measure fine on ESR but the 3300uF 35V snap-on electrolytics have 10 ohm ESR or about 500x higher than expected!
One of the small 10uF 50v/63v electrolytics next to R514 also measures 1.5kOhm ESR
https://xdevs.com/doc/Fluke/8508A/img_cm/Guts_3.jpg3300uF 35v snap-on electrolytics are some ultra-miniature series and I didn't have any in "stock".
Quick&dirty repair with taller 2200uF 35V caps and the unit powers up fine, clears all self tests and runs through the zero routine just fine.
Hopefully this is helpfull with someone working with these dinosaurs. I'd assume that these have come to mature age and failures are more of rule than exeption.
Also question if someone has replaced or measured the electrolytic caps on the "monster relay board"?
https://xdevs.com/doc/Fluke/8508A/img_cm/Guts_7.jpgThey also look like recipe for disaster being next to heatsinked components inside a rather hot running equipment.