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Kenwood Receiver KR-A4070 Issue

Davy49

Jan 21, 2015
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Hello,
Normally I can determine the cause of a problem on my own, but so far anyway..I can't seem to correct the issue I'm having with my kenwood receiver. I've had this for quite a while, and while it's not a top of the line model, it has performed what I needed from a receiver. The problem I'm having with it is that I can only control the functionality of it with the factory supplied remote. When it was new, I could manually press the function key's ( power, tuner, video, etc.) and the desired function would work like it was supposed to. Then, along came some universal remote's that were supplied by various supplier's ( comcast, logitech harmony # 300 & # 650 ), using those remote's I could operate my receiver along with other device's, such as tv-cable box-dvd player, etc. . Now when I try to control the function's manually like I used to be able to, I can't. No matter which function button I press( power,etc.) nothing happens. I can only control the function's by using the factory remote. it's like the function button's are been restricted by being used manually. I've tried resetting the micro computer inside the receiver like is described in my owner manual ( disconnect from power, press the 'tuner' button and while holding it down, plug it back into power). Trying that procedure didn't fix my problem, does anyone have any suggestion's so I can enjoy my receiver normally once again ?/
Thanks,
David
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Hi David and welcome to Electronics Point :)

So you're saying the front panel pushbuttons don't work but remote control does work?

According to the schematic, IC901, the micro on the front panel board, scans the buttons, drives the VF display, and receives the remote control data stream. So it must be mostly OK. Here's the relevant part of the schematic.

272356 buttons schematic.png

It looks like IC901 drives the pushbutton array with positive pulses on pins 62~68 and detects button presses by watching pins 55, 57, 58, 59 and 60. These lines are pulled to 0V by resistors.

We can't make too many assumptions about the logic used by the microcontroller to scan the pushbutton array. For example it's possible that a stuck button could cause it to stop scanning until the button is released, or to ignore presses on other buttons. So I would check for a stuck or shorted button first. With all buttons released, you shouldn't see any pulses on pins 55, 57, 58, 59 and 60.

Edit: A stuck button won't stop it from scanning, since the scanning is tied in with the display multiplexing. But you still can't assume much about how the MCU does the scanning.

There's also something strange happening on pin 61; when the micro drives that pin high, this will force pins 55, 57 and 59 high through D908~911. I don't know the reason for that part of the circuit. Possibly some kind of self-test.

With this information and a multimeter and perhaps an oscilloscope, you should be able to locate the problem. If not, please post again with more information.
 
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Davy49

Jan 21, 2015
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Jan 21, 2015
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Hi KrisBlueNZ,
Thanks so much for such a detailed answer..the front panel pushbuttons don't work (but used to work correctly), and the supplied remote still work correctly. So you don't think by me using a universal remote to operate the receiver in conjunction with a tv - blu ray disc player, had any ill effect on the operation of the front panel pushbutton's ? Of course I have a good multimeter, but not a oscilloscope.
Thanks,
David
 

KrisBlueNZ

Sadly passed away in 2015
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Right, I very much doubt that using the other remote controls would have any effect.

The pushbuttons are scanned one column at a time, multiplexed. This will be a bit difficult to follow without a dual trace scope, but you could try cutting tracks to eliminate the buttons.

Actually I suggest first checking all of the diodes in the circuit. An electrostatic discharge to a button could easily have damaged a diode. We have to hope that it didn't also damage any of the inputs on IC901.

So start by measuring each of the diodes in the circuit. If any of them reads leaky, lift one end out-of-circuit and measure again.

If the diodes are all OK, I suggest lifting one end of D908. You should now measure roughly GND potential (the same potential as on pin 48 of IC901) on all of the inputs - that is pins 55, 57, 58, 59 and 60 of IC901. If any input has a significant positive voltage on it, there's probably a shorted pushbutton somewhere.
 

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Davy49

Jan 21, 2015
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Hi KrisBlueNZ,
First of all..thanks SO much for all of your effort's in trying to resolve this issue with my now older model kenwood receiver. I've gotten many year's of service from it. Today, I'm really take a look in more detail at the push button's on the fron panel. I don't think any are 'stuck', but any thing is possible. For some reason, I still am wondering if SOMEHOW one of the universal remote's I had used previously is somehow still 'tied in' electronically to the micro computer ?
Thanks,
David :confused:
 

KrisBlueNZ

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No problem. No, you can forget the idea that using universal remotes with the unit has somehow stopped the front panel buttons from working.
 

Davy49

Jan 21, 2015
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Hi,
As I already have realized..you are smarter than I am, of course I feel like we all have expertise in SOMETHING ! I've learned a LOT of useful information in my lifetime..to be honest, I'm BLESSED to have been able to consume so much, and to be honest...the more I think about what's going on with my receiver, I'm starting to think like you as far as thinking the microcomputer somehow has retained some kind of a 'signal' or something of that nature that's preventing the use of the push button's on the front panel of my receiver.
Thanks,
David :)
 

KrisBlueNZ

Sadly passed away in 2015
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OK. Get back to me when you've tested those inputs.
 

Davy49

Jan 21, 2015
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OK..will do, I've always wanted to visit New Zealand, I've read about it..I guess all I can do is DREAM.
Thanks,
David
 

Davy49

Jan 21, 2015
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Hi KrisBlueNZ,
Well..I'm just about ready to give up..I've got the receiver opened up, checked all the switches..couldn't find any that were stuck. I guess if I have to, I'll need to think about replacing this receiver. I'm attaching a photo of the front of it.Even though it's getting older (like me) it's still in good condition.
DavidKenwood KR-A4070.JPG
 

Davy49

Jan 21, 2015
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I'm SO happy, the manual portion of my receiver is now working correctly once again, even the push button's on the front panel all felt like they were normally, I gently blew some air into the push button area. It must have done some good, because it's working. Thanks for all of you help on this matter.
David :)
 

Davy49

Jan 21, 2015
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KrisBlueNZ,
I feel the same way, even though this isn't a top of the line receiver by any means..I'm still glad to have it functioning correctly. Thanks again !!
David :)
 
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