warriorjoe
Junior Member
I have an old sony cdx-5460, THE car radio of the '80's, in my old 1979 mercedes 450SL. There is a companion 40W dual speaker amp with speakers under the rear seat shelf.
All devices and features work on the unit except on AM. The AM will play good for about a 1-2 second burst them drops to low volume hiss. Flip back to FM, plays good continuosly. Then flip to AM, hear initial 1-2 second burst of good audio, then nothing (except low volume hiss.) This action can be repeated indefinitely. I not only like listening to FM, but am also an AM talk-radio junkie, which is why I am missing that AM!!
Now, I am not a newbie at electronics repair. I am a retired electrical/electronics/computer and broadcast engineer with extensive experience designing and repairing all types of consumer and industrial electronics including computers, TV's and radios. I know how to use a scope and audio test equipment. I say that not to toot my horn but to provide that backdrop to lead into a technical discussion that is probably a cut above the average forum question. If no one can answer it, I will understand. But hopefully someone else with similar background and/or experience will be able to help me. So here goes...
I have a Sony service manual with schematics and component layout and parts lists for all the main components. However there is not a seperate schematic or parts list for the tuner unit, which I think is where the problem is.
I can insert a 1000 hz audio signal into the first audio stage chip, and get a good tone output through both channels. So I know all the audio circuits are OK, and as I said earlier everything works fine in FM mode.
Using a techtronix scope, I can determine the existence of all the expected signals coming from the tuner in both AM and FM modes EXCEPT at the "AM-Det" output. When excercising the unit as described above, when switching from FM to AM, the voltage on that "AM-Det" pin from the tuner quickly rises from 0.0 to over 6 volts and settles back to about 3.52 volts (manual lists 2.2V). Scope trace shows good audio on that pin for about 2 secs then goes to no audio. I have a capacitor ESR tester and have checked all the electrolytics in and around the tuner unit and they all check OK.
The service manual shows part number A3282-000-A for the tuner unit. It is constructed of both chips and other discreet surface-mount components like the main board, so I would think a schematic diagram exists somewhere. I would like to repair the unit if I can, even tho it is an old unit and does not have all the bells and whistles of today's radios.
I any of you guys/gals have access to the tuner schematic, or have knowledge of the described symptoms and perhaps possible solutions, I would be eternally grateful to you!
BTW, all I get from Sony is the address of my local authorized Sony repair shop, which has proved fruitless.
Thanks in advance.
All devices and features work on the unit except on AM. The AM will play good for about a 1-2 second burst them drops to low volume hiss. Flip back to FM, plays good continuosly. Then flip to AM, hear initial 1-2 second burst of good audio, then nothing (except low volume hiss.) This action can be repeated indefinitely. I not only like listening to FM, but am also an AM talk-radio junkie, which is why I am missing that AM!!
Now, I am not a newbie at electronics repair. I am a retired electrical/electronics/computer and broadcast engineer with extensive experience designing and repairing all types of consumer and industrial electronics including computers, TV's and radios. I know how to use a scope and audio test equipment. I say that not to toot my horn but to provide that backdrop to lead into a technical discussion that is probably a cut above the average forum question. If no one can answer it, I will understand. But hopefully someone else with similar background and/or experience will be able to help me. So here goes...
I have a Sony service manual with schematics and component layout and parts lists for all the main components. However there is not a seperate schematic or parts list for the tuner unit, which I think is where the problem is.
I can insert a 1000 hz audio signal into the first audio stage chip, and get a good tone output through both channels. So I know all the audio circuits are OK, and as I said earlier everything works fine in FM mode.
Using a techtronix scope, I can determine the existence of all the expected signals coming from the tuner in both AM and FM modes EXCEPT at the "AM-Det" output. When excercising the unit as described above, when switching from FM to AM, the voltage on that "AM-Det" pin from the tuner quickly rises from 0.0 to over 6 volts and settles back to about 3.52 volts (manual lists 2.2V). Scope trace shows good audio on that pin for about 2 secs then goes to no audio. I have a capacitor ESR tester and have checked all the electrolytics in and around the tuner unit and they all check OK.
The service manual shows part number A3282-000-A for the tuner unit. It is constructed of both chips and other discreet surface-mount components like the main board, so I would think a schematic diagram exists somewhere. I would like to repair the unit if I can, even tho it is an old unit and does not have all the bells and whistles of today's radios.
I any of you guys/gals have access to the tuner schematic, or have knowledge of the described symptoms and perhaps possible solutions, I would be eternally grateful to you!
BTW, all I get from Sony is the address of my local authorized Sony repair shop, which has proved fruitless.
Thanks in advance.
