Hey Mark, can you tell me (if you know) how the FM Signal Strength is reported back to the Empeg for display on the screen?

If it's a serial message, could you tell me what that message is so I can set up a sniffer to look to see what mine is saying?

Thanks,

-Ben

Dunno. I think all of that is closed source, inside the player application. I think.

It seems pca would be the one to ask.

From his tuner kit manual, there is a signal wire and a level wire going back to the empeg. I've been meaning to see if I can defeat the signal strength meter with this wire.

Oh, well in that case, if the level wire goes all the way to the empeg, then it must connect to the saa7705h DSP chip. The datasheet for that will describe where it goes from there, and it undoubtedly is readable from a DSP register.

EDIT: from perusing the datasheet, it seems that the FM level info gets rolled into a noise measurement that can be incorporated into the RDS data, which is read out and processed by the player app.

-ml

What I think you should do for diagnostics here, is to temporarily route the level output of the RF module to the radio in place of the MPX output, thus bypassing the part of the RF module which usually goes bad.

If you can hear (tinny) proper sound instead of just noise with that, then we know it's the usual component failure inside the RF module.

I use a small portable amplifier for that here, just touching the probe (amp input) to the level line, and then to the mpx line, and then back again.. and so on, to compare the two outputs.

-ml

That's just it - I get audio just fine... it's only the signal bar that shows on the display that tells me I have no signal.

BTW, I LOVE that signal tracer. Very funny. (and simply practical)

My scope shows me nice hot outputs that completely correlate to the datasheet for the tuner module.

watching the RDS MPX is fun too. I had an RDS decoder around someplace.. I wonder where I put it.

ANNnnyway... Thanks for the info (why they didn't work it into the onboard PIC and just do a serial command is weird.) I'll trace the Level line (haven't worked on it yet) and see if it does indeed work back to the empeg cable. I wonder if my empeg connector is just unhappy since I'm pretty religious about pulling it out of the car when I'm not with it.

-Ben

I'm looking at the saa7705h datasheet now. So many neat chips. So little time.

Ah, okay then!

Next, find the level-input pin on the DSP, and see if the signal makes it to there all of the way from the radio.

And, yup, check those connectors!

Ok, from what I can see so far, the Level output runs to an LM258 Op-Amp and then to one of the Analog inputs on the onboard PIC16C73...



UPDATE: I do see something that looks like it mirrors the level output on one of the empeg pins. (shaking head) Need to trace further. But because there is only 7 pins in use (one socket is empty) that makes:

So that leaves:

PWR, GND
TX, RX
FM-MPX
AM-Audio
Level (AM/FM)

So now where does RDS fit in?

-Ben

PCA gave me the info I needed to confirm that my tuner is probably working just fine.

I need to dig into my empeg at some point now to see why the voltage isn't getting read out properly.

I'll be checking the DSP next (at some point)

-Ben