HA11211 signal strength and tuning led's

Nitrohead

New Member
Hello and thank you for reading this post.
First and foremost although I've dabbled with electronics over the years (mainly digital and a bit of analogue) I am TOTALLY green with RF so excuse me if my use of terminology is quite a bit off.
I'm struggling with a HA11211 based FM/AM tuner section of a micro component system that refuses to drive the signal strength and tuning led's. Radio broadcast reception on FM and AM works fine with no apparent issues (weakness of signals, clarity, tuning problems etc). The problem here is solely with driving the 5 led signal strength meter and tuning meter (3 led's left centre right).
My understanding of the 11211 so far is that the signal strength level is fed out through pin 9 (in my case) to a BA695 pin 3 (3 led tuning IC) and a LB1416 Pin 3 (5 led driver).
Interestingly touching pin 8 with a length of wire does (besides inducing a lot of other radio stations on the audio) raise the voltage of the 11211's Pin 9 to about 1.4v and the signal strength meter hits 2-3 led's so this leads me to believe that the 11211 may not be behaving correctly. I replaced the HA11211, BA695 and LB1416, tested all supporting resistors but all symptoms persist. Its as though the 11211 is not receiving a strong enough signal in the first place from the earlier IF stages (even though I must admit the audio levels sound perfectly fine). Could the Ceramic Filter be filtering fine but over attenuating the signal? Is this a typical symptom of a failing CF or should I be looking elseware (earlier IF stages?). Or maybe am I'm getting this all wrong?
Thank you
 

Attachments

  • CMC-5 Schematic.png
    CMC-5 Schematic.png
    487.4 KB · Views: 28
Datasheet for HA11211 in English finally found and has helped tremendously to understand what voltages I should have floating around the 11211 pins - but not enough to nail the issue ! I'm no longer of the opinion that the Ceramic Filter or low input to the HA11211 has anything to do with the problem since the datasheet expects a typical value of around 1.9v on the signal input Pin 8 (out from the C.F.) and that's precisely what I have. So am beginning to think that the circuitry on Pin 9 may be zapping the signal. Datasheet says that Pin 9 should have a minimum of 0.5v and a typical of 1.8v with a signal of 70 dBu on Vin (which I expect is Pin 8) and a min of 3v and typical of 4.4v with a Vin of 100 dBu. Not yet entirely sure how to interpret these Vin values. ny help would be much appreciated.
 

Attachments

  • HA11211 DataSheet.pdf
    409.5 KB · Views: 31
Progress - Isolated HA11211 Pin 9 from circuit and drove circuit with a range of 0-5 volts. Signal Strength Led's lit up as i increased voltage. Tuning led also flashed indicating that the LB1416 and to a lesser extent the BA695 and supporting circuitry are fine.
Isolated Pin 9 throws 0.0026v for no signal and 0.2v at strongest signal (tuned into a radio station).That's way below what the datasheet says I should be expecting! All points toward a faulty HA11211 but its already been replaced so could this be a dud or am i facing faulty supporting circuitry ?
 
Unusual HA11211 pinouts particularly 17 and 18 deciphered - here's the pinout for the HA 11226 which has an identical 16+2 DIL package layout as the HA11211
 

Attachments

  • HA11211 Pinout.jpg
    HA11211 Pinout.jpg
    78.9 KB · Views: 21
You seem to be doing all right with what you're doing, Nitrohead. I'm not sure why you haven't got any responses to your post, although that schematic you posted is terrible. If you have a higher res version of it then maybe you could post only the relevant portion at a higher resolution.

Looking closely at the passives in the path between the HA11211 and the LB1416 might indeed be a good idea. If you unload the pin 9 output, does the voltage there rise to a reasonable level?

The pin numbering on that HA11211 is pretty amusing.
 
Thanks for your encouraging feedback and notification of schematic quality. I'm attaching a pdf version of the tuner section.

Unloading pin 9 does not change the voltage level coming out of it. So on that observation it may be that either the replaced 11211 is faulty or the supporting circuitry maybe keeping pin 9 low.

Mysteriously touching pin 8 (IF input) with a 30cms length of wire induces the reception of interference from lots of other stations (expected I guess since i'm bypassing the 10.7Mhz ceramic bandpass filter altogether) and pushes the voltage of a loaded pin 9 to rise to 'expected' levels in fact high enough to register 4 led's on the signal strength meter !

Could this mean that the 11211 has the capability to drive pin 9 correctly and that therefore the IF input level to pin 8 is low? If the latter is to be considered plausable - could it be that the ceramic filter is over-attenuating the filtered signal?
 

Attachments

  • CMC-5 Tuner Section.pdf
    378.2 KB · Views: 15
When you are tuned to an FM station with (as you said at the top) "no apparent issues (weakness of signals, clarity, tuning problems etc)" and such that pin 9 is outputting (only) 0.2 Volts, what is going on with muting and mono/stereo? Is the muting level overcome? Is there stereo? Because those would both be indications that the signal level is actually OK.

The graph labeled "Signal meter voltage vs. input level (FM)" in the HA11211 datasheet says that pin 9 will output 0.2 volts when the HA11211 input level is at about 45 dBµ. The muting sensitivity is listed on page 3 as 48 dBµ. The HA11211 outputs the muting control voltage output on pin 10. (There is plot for that output vs. input level in the datasheet as well.) Note that 45 dBµ is also a level at which you would still expect to have some noise in stereo audio output.

If you think the IF signal is just low, you might look at the "How to clean a tuner (analog)" sticky in the Tuners forum. The consensus on AK seems to be that messing with the RF section beyond that is not a DIY proposition. On the other hand, if the muting and stereo behavior is telling you that you have a stronger input to the HA11211 than the signal meter output indicates, then you're back to looking at why that is.
 
Thanks for your feedback Audiotemp

In answer to questions:

Mono/Stereo - the switch functions correctly and toggles the broadcast from mono to stereo as expected. Stereo LED lights up on Stereo broadcasts as expected and turns off when the Stereo/Mono switch is pressed to Mono mode. For completeness, the stereo led also turns off in between stations as expected.

The FM Stereo/Mono and muting switch are operated by a single mechanical switch. so to carry out these tests I disconnected the mute wire from the switch in order to operate the Mono/Stereo function independently of the mute function.

Switching on the mute actually kills the audio completely so this would indicate that the muting level has not been overcome.

I carried out tuner cleaning as instructed but no difference in behavior was noticed.

Other observations:
Pin 10 -
With Mute switch turned OFF - Muting control voltage Pin 10 rises to 5.06v in between stations and drops to 3.2v when tuned into a station.
With Mute switch turned ON - Muting Control voltage Pin 10 rises to 4.7v inbetween stations and drops to 2.2v on a tuned station. (tuned prior to activating mute)

Pin 9 rises to 0.34v when tuned into a station and drops to 0.002v in between stations. Mute on/off makes no difference to these readings.

Could the Ceramic Filter be over attenuating - is this a typical or unheard-of symptom of CF failure ?
 
Another observation - (managed to get hold of some neat kit to help me along the way, Oscilloscope, Signal Generator etc)
I injected a 2kHz FM sinewave signal to Pin 8 and the signal strength meter came to life. Signal meter registered higher as I increased the injected frequency. 1kHz 2 led's, 2kHz 4 led's. I was also able to hear the injected signal through the speakers. (this indicates that the input from IF stages may be suspect)
Whats interesting is that when activating mute, the audio (1kHz FM sinewave) dies but the signal strength led's keep lit ! (not sure what to make out of this at the mo)
 
I can't answer your questions about the ceramic filters, or to give you a lot of advice on what more you can do with the equipment you have. I'm going to ask that this thread be moved to the Tuners forum and see if that helps you. I would think though that you could get some idea of the signal loss through those filters using your oscilloscope, although of course you will be disturbing things by probing them.

As far as the HA11211 goes, it outputs a signal to the BA1320 MPX chip telling it to mute the outputs. I would not expect the signal level LEDs to be affected by that. Your various reports have largely convinced me that the HA11211 is not your problem.

You might also trying looking for threads about whatever specific question(s) you have, like the ceramic filters.
 
Last edited:
To be clear, the signal strength LEDs do not work on either FM or AM ? If that is the case it eliminates anything that is particular to only the FM or the AM sections. It appears that you are doing all of your testing in the FM mode.

"Switching on the mute actually kills the audio completely so this would indicate that the muting level has not been overcome."

This may be important information. Does this happen when receiving a know strong station. And I have to ask, are you using an adequate antenna?

Ceramic filters have been known to fail. They can fail by going high impedance in series with the IF signal or low impedance to ground for the IF signal. Either case will reduce the IF signal. Look at the input and output of the ceramic filter with the oscilloscope when the receiver is tuned to a known strong station. Also if the FM local oscillator's amplitude is lower than it should be that can reduce the level of the IF signal.

Just as a starting point be sure that the FM RF amp trimmer capacitor is correctly adjusted and that IFT1 is correctly adjusted.

If you have an RF signal generator you can inject an RF signal at the base of Q2.

If you do not have an RF signal generator you can for simple test, connect a 2 foot long or so piece of wire to the base of Q2 and tune in a known strong station. This will bypass the first tuned RF stage and its transistor. Does this change the symptoms, muting function and or signal strength LEDs?

Basically if you have not done so, you want to be sure that the RF front end, local oscillator and the mixer stage (including the adjustment of IFT1) are doing their jobs correctly. If so then you can move your testing downstream.
 
You can jumper around a ceramic filter preferably with a small ceramic cap (ie 0.01uF) in series with one lead of jumper. I have just replaced the 3 ceramic filters in my SX-939 because of poor FM sensitivity, but this doesn't seem to be the problem with the OP's issue as he stated that sensitivity is fine, just that the LED's aren't working?
 
Back
Top Bottom