Hi all, this tuner works fine most of the time. The issue is with manual tuning. At the upper end of the FM band around 107 MHz sometimes it becomes unresponsive. When it happens I can't change frequency up or down, the only remedy is to turn it off and on. Then I can change frequency with auto scan or in manual steps again up to 108.0 MHz and it will fold over to 87.5 MHz as it should, it works in both directions... until it freezes again. It is a synthesized tuner. Could it be the prescaler chip at fault?
Schematics here:
https://www.electronica-pt.com/esquema/old-tv/marantz-vintage/marantz-st-54-schematics-31705/
Service info here:
https://archive.org/details/manual_ST54_MARANTZ
Schematics here:
https://www.electronica-pt.com/esquema/old-tv/marantz-vintage/marantz-st-54-schematics-31705/
Service info here:
https://archive.org/details/manual_ST54_MARANTZ