I am pretty sure I have an error in my tuner kit assembly. Do we not get a schematic due to non-disclosure issues? It would help for troubleshooting. I have hooked it up to the empeg and I get VERY FAINT audio on both AM and FM. actually only a few stations produce anything audible. They all show very high signal strength. Additionally IQ with only power and ground applied to the tuner unit is 130mA which seems high.

Any advice in tracking down the problem is apreciated. If I knew what the SPDT (the maxim chip) was used for I might lean towards it as I accidentally soldered it in wrong once and had to remove and replace it once.

HELP...

Thanks,
Eric Fesler (BSEE but too sloppy to be a good technician)

There is a chance that the problem is not in the tuner module itself. If the signal strength meter is high but the stations do not come in well, it sometimes means a problem with wiring pinouts on the connector that hooks the tuner module to the player. It can also sometimes indicate problems with the antenna connection. Since those are easy, check them first.

I checked the pinout on the back of the sled. Everything is correct as far as I can tell. Problem is the FAQ only shows TUNER for the wires that go to the tuner module (as far as I can find). The tuner module molex and sled-to-tuner molex have colors matched "straight-thru".

Really hoping somone with a tuner module near a bench can confirm quiescent current for me.

Eric

I've just completed assembly of my tuner kit and am having the exact same problem. The tuner is functioning; it powers up and I can seek both on the AM & FM band. It will lock on the local stations no problem, but the audio level is almost non-existant. I'm not an audio or electronics engineer by any means, but I dare say it sounds similar to trying what you'd hear when trying to drive a small speaker with an unamplified (line level) signal.

Any more thoughts out there?

-Randy

Antenna connection correctly made at tuner board and at antenna socket?

All components checked to be the correct way round during construction?

Would suggest you go back and run through the build a second time - what you describe is a functioning processor board being recognised by the empeg, but the tuner board itself, or the demodulation/signal amplification is going wrong somewhere.

Ok, now I'm getting somewhere. I was just sitting out in the Jeep going over the tuner kit processor board with my meter and accidently shorted pins 2 and 3 on IC 7, which is the CA3140 (CMOS Op amp). For a split second, everything functioned as it should. Of course I tried it again and got the same results. So now I'm looking at a .pdf schematic for the IC and can see that pins 2 and 3 are the inverting and non-inverting inputs (respectively) for the Op amp.

And now I'm pretty much in over my head as far as being able to deduce what is or isn't happening that's preventing the tuner from working the way it should. Is there a way that I can test the IC? Does anyone know what the signal is supposed to look like that is passed to those inputs and where it originates?

Rob- Thanks for the tips. I followed your instructions for the co-ax hook-up to the tee. What a help that was! I do believe that all the components were installed correctly; I was extremely meticulous about the whole thing. The whole time I was putting it together I was taking my time thinking to myself, "I'm only going to do this one time".

I hope that the others that were experiencing the same symptoms can find my clues useful.

I'll get this working yet!

-Randy

I've spent a little more time going over each solder joint on both bords making sure that they're good, and that there aren't any shorts. I used this picture of the boards and the traces along with my multi-meter to trace back from my problem area, IC7, through IC8 (SPDT switch) back to the tuner. All the connections appear to be fine. All the components are oriented correctly. I don't know what else to check at this point.

I can borrow a scope from a friend if there is someone out there who can tell me what the signal is supposed to look like in a few places.

I'll keep posting my findings, but at this point, unless it comes to me in a dream, I'm afraid I'm pretty much stuck.

The thought of just shorting pins 2 & 3 on IC7 had occurred to me, but I don't feel that's a proper solution. Besides, I have no idea what side effects that may have.

-Randy

Hi.

I've been puzzling over the problem described here, and looking at the circuit diagrams trying to figure out what the problem could be. A clue is the report that shorting pins 2 and 3 of IC7 makes the audio come through OK.

IC7 is an op-amp configured as a non-inverting unity-gain buffer, to isolate the FM multiplex signal from the tuner by way of the MAX4544 switch from the outside world. The RF level signal comes directly from the tuner module, so if there was a problem with the multiplex signal it is feasible that the software could report a full-strength reception while producing a faint audio output.

A unity gain op-amp is produced by having the gain-producing feedback component (normally a resistor) set to 0 ohms, thereby forcing the amp to a gain of 1, but with a very high input impedance. This means that pins 6 (output) and 2 (inverting input) are directly connected together, since a convenient 0 ohm resistor is simply a PCB track. If subsequently pin 3 is shorted to pin 2, this effectively means that 2,3,and 6 are all connected together, therefore bypassing the buffer completely. If at this point the signal level comes up to the correct value, it strongly implies that there is a fault with the op-amp.

This could be a power supply fault, so check that there is +9v present on pin 7. Also, for the sake of completeness, check that is actually IS a CA3140 at IC7! Mistakes can be made

Assuming all this is OK, also check that R13 is the correct 220 ohm resistor, and that you haven't accidentally used a different one.

If this all checks out, the only thing I can really think is that the chip itself is actually bad. If you can remove it and replace it with another one which then works, this would prove it. However, a workaround is as you suggested, which is to bridge pins 2 and 3. It's a little dirty, but I can't see any particular reason why it would cause problems, other than perhaps an increased susceptibility to induced noise from external sources, especially if the cable between the empeg and tuner is extended. The tuner module is still isolated by the MAX4544, so it should be safe enough.

If you want I can send you a replacement CA3140, but they are only a few cents apiece so if you can get one locally it would save a lot of effort. I have to admit I am curious to know if the chip really is bad. I can't see any other possibility, but bad chips are normally pretty rare.

pca

Patrick, thank you! I was so sure that there was something wrong on the signal side of things I completely ignored the obvious- to make sure that there was good power to the chip. DOH! After reading your last post, and doing a quick check, I found that my soldering job on pin 7 was bad, and the chip was not getting power. A little heat, a little more solder, and I now have a 100% working tuner (and some experience).

Thanks again for all of your efforts and additional insight into what makes this thing work. I'm guessing that at least one other person with similar problems will find all of this helpful.

Cheers,
-Randy