Hello

Got this old receiver for free with problem, none of the front panel buttons are responding.
I was able to turn it on with remote and everything seems to work with remote controler.
Found shematic (not best quality) and what i don't understand how this switch matrix works (or should work).
So on 6v a have 5.65v i guess its fine, only bad component on the board was C307 supercapacitor ( i assumed it is only for voltage stabilization and for now i desoldered it out).
I don't understand why we have both and pull up and pull down resistors on switch matrix, so when i press any switch i have voltage divider, and on ic input key-1 have only 0.5v (pull up resistor are larger) but ic does not respond . Is that ok ?

 

Hi,
Do you have +5v at pin 6 on connecter CN302 ?
Forgive me, if you are already beyond that point.
Good luck.......

 

Yes at pin 6 on connector cn302 i have 5.65v I wrote confusedly in the first post, sorry.

 

Check the voltages on each of the key input lines and key SEG lines. You likely have a "stuck" switch or an open line. A scope will be your friend here. Check the clock lines too.

 

Thank you for reply, checked some voltages and made some progress. On SEG3 and SEG4 measured only 1.2v so i desoldered one end of pull up resistors on those lines and all other buttons started to work.

Still cant figure out how i could have there only 1.2v when all switches are open, that means whole side
hanging it should be 5v?

For clock i have only analog oscilloscope but i guess can be done.

 

Just a quick update, desoldered few micro swiches even they measured ok with continuity (from those two SEG lines) and guess what, all lines now have same expected voltage. Tomorrow I will solder new ones and test it....