Hi,

I wonder if I could tap into some collective insight here while waiting
for a manual and schem, (thanx Joe), here's where I'm at with the radio...

1. The machine comes on, I get a display, all leds for frequency bands
are on, Iguess that only FM, default, or the last band selected should
be on) half of them dimmer than the other half. Can repeatedly turn
radio off and on if no other function/button is selected. If I push a
button of two, I can neither turn the machine off, nor select any other
bands, have to unplug...

2. When the machine sits a bit, off (power plug attached) It comes on,
and now I am even able to tune a bit w/ the encoder, and even key in a
frequency, and it changes, and plays a bit, then dies...Letting it sit a
couple of minutes, it can be switched back on, and tunes and plays a bit
more, starts to growl...and then the sound stops, its stuck and I turn
it off..


While I'm not even a mediocre tech, it sounds like a cap is initially
empty, charges, then starts to leak...IIRC, a power supply cap, or drop
in ps voltage might be might explain the growl.....
Maybe the same in the 5v supply? Or should I freeze spray the thing???

The radio uses, AFAIS, among others,

M5840 cpu
MM5481 led driver?
MM5368 oscillator
TDA1571 mixer
TDA5700 radio chip

Anyway, would really appreciate some help....


regards,

nikos

Nicolas Boretos wrote:

1. The machine comes on, I get a display, all leds for frequency bands
are on, Iguess that only FM, default, or the last band selected should
be on) half of them dimmer than the other half. Can repeatedly turn
radio off and on if no other function/button is selected. If I push a
button of two, I can neither turn the machine off, nor select any other
bands, have to unplug...

2. When the machine sits a bit, off (power plug attached) It comes on,
and now I am even able to tune a bit w/ the encoder, and even key in a
frequency, and it changes, and plays a bit, then dies...Letting it sit a
couple of minutes, it can be switched back on, and tunes and plays a bit
more, starts to growl...and then the sound stops, its stuck and I turn
it off..

Power isn't getting to where it should be. The supply rails somewhere
are too low.

While I'm not even a mediocre tech, it sounds like a cap is initially
empty, charges, then starts to leak...IIRC, a power supply cap, or drop
in ps voltage might be might explain the growl.....
Maybe the same in the 5v supply? Or should I freeze spray the thing???

Get out the meter and start checking the power supply voltages. After
checking them AT the supply, start checking them in other places because
you may well have a cap that is intermittently shorted and pulling down
the supply rails. Also feel around with your fingers and see if you
can find anything hot.

One trick I like for finding bad decoupling capacitors is to bridge a
large bench supply across the supply rails. If a cap is partially shorted,
the high current suddenly available from the bench supply will usually
make it fail catastrophically. Note that it DOES sometimes take out
board traces so be careful.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."