stenzer
Advanced Member level 3
Hi,
I got a KT-3050L Stereo Tuner from Kenwood for repair. The service manual can be found here (and attached). Below I have attached an excerpt with measured voltages. Luckily the service manual states the expected voltages. In gerneral, the display is completely dark, and at least the STANDBY indicator should light up when the tuner is connected to the mains. To power up /wake up the tuner it seems a HIGH signal from the MCU (IC10 - µPD78043GF-011) is needed/missing (lower rigth, colored in red).
According to the measurements theo output of IC11 (PST528D) is not as expected, which is a reset IC. As the base of Q46 is AC coupled and I measured a voltage there, it looks there must be some "switching" going on. Until now I only performed measurements with a DMM. I also removed IC11 to check what's going on. This results in an output voltage 4.7V (instead of ~2.25V) and the base voltage of Q46 is 0V. Nevertheless, the tuner does not work. What confuses me is the !CE (active LOW) pin #18, which I assume is the Chip Enable (?), so I would assume that pin has to be LOW to enable the MCU, instead of 5V as indicated. Or is there a proper reset sequence required during startup? I was not able to find the datasheet of the µPD78043GF. I only found the datasheet the UPD78043A, which does not have a !CE pin.
I would appriciate any suggestions which allows me to fix the tuner.
Thanks!
I got a KT-3050L Stereo Tuner from Kenwood for repair. The service manual can be found here (and attached). Below I have attached an excerpt with measured voltages. Luckily the service manual states the expected voltages. In gerneral, the display is completely dark, and at least the STANDBY indicator should light up when the tuner is connected to the mains. To power up /wake up the tuner it seems a HIGH signal from the MCU (IC10 - µPD78043GF-011) is needed/missing (lower rigth, colored in red).
According to the measurements theo output of IC11 (PST528D) is not as expected, which is a reset IC. As the base of Q46 is AC coupled and I measured a voltage there, it looks there must be some "switching" going on. Until now I only performed measurements with a DMM. I also removed IC11 to check what's going on. This results in an output voltage 4.7V (instead of ~2.25V) and the base voltage of Q46 is 0V. Nevertheless, the tuner does not work. What confuses me is the !CE (active LOW) pin #18, which I assume is the Chip Enable (?), so I would assume that pin has to be LOW to enable the MCU, instead of 5V as indicated. Or is there a proper reset sequence required during startup? I was not able to find the datasheet of the µPD78043GF. I only found the datasheet the UPD78043A, which does not have a !CE pin.
I would appriciate any suggestions which allows me to fix the tuner.
Thanks!
