A while back, my tuner reception went bad, and I'm trying to figure out what might be going on. The symptoms are:

1. FM reception on most channels is non-existent, but on a few channels, it's quite clear.
2. The FM channels that come in clear now are ones that I don't remember being very strong before.
3. Channels that were strong before are 100% static now.
4. AM reception is very poor, with high pitched whining on all channels.
5. Behind the high pitched whining, I can hear some of the stronger channels, but just barely.
6. The change from good reception to horrible reception seemed to happen overnight. One day I could listen to dozens of AM and FM stations, the next day almost all of them are static.

I pulled my dash apart tonight to see if it was an antenna connection problem, but couldn't find anything wrong. As I jiggled the antenna around I could get a tiny bit of signal on some channels that weren't coming in previously, but the improvement was almost negligible. The red light on the back of the tuner was on, and the tuner seems to be operational other than the horrible reception.

Anyone know what might be going on? Would a replacement tuner module solve the problem?

I would guess that more likely it's a bad antenna connection or bad antenna ground.

How would I go about confirming this diagnosis? I should note that if I disconnect the antenna wire from the tuner module, reception gets *way* worse -- so it's not like the antenna connection is completely dead.

One other data point I discovered today is that on the AM dial, no matter what station I select, I get a faint signal of one particular station at 1020 kHz. That station happens to be the strongest in my area, but I find it strange that I can hear it even if I go all the way to 1400 kHz I can still hear that same station.

My antenna is in my car's glass, if that makes any difference...

I disagree with Shonky. I don't think it's a bad antenna connection. It sounds like bad wiring between the empeg and the tuner, or a bad tuner.

Double check that you haven't lost any wiring connections between the tuner and the empeg, then start going down the "bad tuner module" diagnosis road. Heck, I'd just say send Stu the module right now. Or, if you happen to know a local empegger, have them bring over their module for a test swap.

Since he's getting diode detection of the strongest AM station, I don't think it's in the external wiring. It's something in the tuner.

This sounds like the classic tuner death syndrome that afflicts factory tuners. There's a tiny IC (op-amp?) inside the sealed RF module that dies for whatever reason, and the result is nearly always static on FM, and sometimes reception on AM.

I've been addressing that by replacing the RF module with the one used by PCATS tuners, with a bit of pin hackery.

If this is what's really wrong with tonyc's radio, then that's probably the only option for repair. A full PCATS kit might be an even better option, since most of the cost is in the RF module.

Cheers

Yeah, if that's the case, I'm going to have to order an assembled PCATS kit. Is anyone stateside still building them, by any chance, or do I have to order from the UK and deal with expensive shipping?

Definitely (re-)test it, by disconnecting the car antenna from it, and using a long length of wire as a temporary antenna instead.

Household 14AWG romex works fine, as does a paperclip in my office here.

Cheers

All I had handy was 12AWG Romex. I connected it tonight and got marginally more signal than no antenna at all (well, the static was louder, anyway), but couldn't actually get any stations, FM or AM. With the car's antenna, I'd at least get a bit of signal on a couple stations as described above.

Is this what you'd expect from a defective tuner?

Yup.

I wonder if that's not what's wrong with mine. I still get stations both local and 50miles (80km) away.

I just show no signal strength even though RDS even pops up.

I will add that the Stereo indicator blinks out a lot (but only shortly. Like a 98/2 on/off duty cycle..

-Ben

p.s. Sealed, eh? Maybe I should take a looky. Anyone know what chip is under there?

OH! Wait - it's in the RF section? Probably a gain-stage.

(not as much an op-amp as it is a common-emitter style gain block.)

I'm gonna crack open my tuner and take a look asap. THAT could definitely be the failure mode I'm dealing with right now.

-Ben

Open up the radio, but not the sealed RF tuner module. Instead, you can probe on the pins from it to see if this is really the problem or not.

You'll have to poke at the datasheet for the RF module (microtune 1384 ufc/wfc, or 1385 ufc) to see which pins mean what, but I could get FM audio from an earlier output when probing around the dead component.

Eg. on the 1384wfc, pins 15-18 -- one of those had (muxed) audio, but the final output did not. Thus the failed component was between those two pins, whichever two they were.

Cheers

In this block diagram of the sealed RF-Module, you can see what I mean.

The Level output had (scratchy) audio from FM, but the final FM/MPX output had nothing. Nothing on the RDS/MPX output either. So the failed component was therefore the FM-Demod stage, or the op-amp immediately following it.

Gah. I hate google sometimes. Anyone (Mark?) have the datasheet handy? I have the 1385 unit.

-Ben

Ah, well then, all you need is the above diagram, and the pin-out list:

ok, I'll let you know what I find.

I'm going to desolder the top tonight.

-Ben

Hey -- this Chip (TEA6848H) can tune US Weather band!

Does anyone know if this capability is available down the line? That would be so cool if the Empeg could still do this.



-Ben

Not all of the empeg tuners supported weather band. Some of the production ones and some of the PCATS ones were US weather band capable but not all of them.

If you can write something to send the proper commands to the tuner via the serial port then it'd work.

Yeah, the weather band thing was discussed on this BBS before. They never put it into the software because of what was already mentioned: Not all of the tuner modules had that available.

Bummer.

Anyway - From what I can see, my pinout is different from the one you provided Mark. (although I appreciate the post)

Is there a thread on here that describes the operation of the radio module (as a whole) with the tuner module? I see the tuner is I2C based.. and I see the radio PCB has a PIC16C73B on there. What's it's purpose?

From what I can tell, there's no (with Mark's info and what I'm seeing on this IC) that there's no L/R output for Stereo. So I'm guessing that's being done elsewhere...

I'd love to hear some expert info since I'm just tearing into this for the first time.

The empeg DSP does the FM MPX decoding.

The PIC converts serial commands from the empeg unit into I2C commands for the tuner module. Documentation on the tuner module is/was floating around the forum at some point.

Mark's pinout is for the tuner module and not the chip inside.

That part I got...
and I'm saying.. it's different from the module I have in my hand.

I can with absolute certainty that RF_IN in pin 1 while RF (and Pwr) Ground is on pins 2 and 5. While the power supply is connected to 3 and 4. Mark's list shows 22 pins, my module only has 16.

That tells me enough right there to know there's something different going on.

Thanks for your input though. It all helps form the "picture" a little faster.

-Ben

Datasheet for Temic 1384. I can't find the datasheet for the Temic 1385 that you have but I assume its the same as it matches up with what you saw. Not sure what Mark posted.

I found a datasheet for the 1384 UFC.... and it more closely matches the first sets of pins (and the number) of my module.

(thanks for the link, but I already downloaded the same thing. Hilarious)

Anyway - I see now.. the 1834/1385UFC (what I have) has 16pins
while the -WFC module has the >16pins...

Moving along....

-Ben

I've not got a tuner module handy at the moment but the PCATS tuner construction manual shows it having a 1385UFC 3x0197 that has 22 pins...

Basically, you're on your own. It *should* work but nobody has done it. Patrick and Hugo never mentioned anything about the PIC not being able to passthrough the necessary commands to the tuner.

Wow - so there's no rhyme or reason. Nice.

Well -- I'm gonna crack out my Comm analyzer next, but the prelim numbers from a really strong nearby station show me:

Audio @ FM-MPX: ~1.5Vp-p (sounds good - manual lists 75KHz=606mV (I'm assuming peak and not p-p))
Level Output: 3.43V (how many bars does the empeg show that as? and I'm assuming that's reported by the PIC on the Tuner Module? and the 1384ufc datasheet states 0-7VDC for the range with 3.3V = 100uV )

If I turn on the scope's FFT, I show the S/N being pretty darn good. (It's fun looking at the spectrum of an FM signal)

When I get my comm analyzer hooked up, I'll edit this with a real SignalIn = Level reading.

Yeah, the PCATS radios use RF modules with more pins than the factory tuners -- a superset of pins, actually.

And there's some mislabelling somewhere for the factory modules -- I seem to recall that the number on the module doesn't match the datasheet number/name.

But it looks as if he's got it sorted now.

Cheers

Ok, then... it seems my tuner module is working ok. It's putting out voltages on Level pin that make sense for a given input.

(i.e. it's maxing out while my display still shows no bars of signal.)

So if the PIC is reporting that level via serial port, something broke there.
If the receiver is reporting the signal via I2C -> RS232, something's broken there.

I'm going to solder my receiver back in more fully.

-Ben

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