Hello SABA friend,

Google translator has a problem with translation of technical terms into German. In this case, "Stimmnadel" is unknown.
Can't understand: "...aber die Stimmnadel erkennt es und die Stimmnadel bewegt sich nicht".

Perhaps we can communicate easier in English? Can you post your technical problem in English? Google translator will work better with English than with German.

I understood that you have no FM reception, but you need to describe more observations:
a) Is FM absolutely silent (muting must be switched off) or do you hear hiss/noise?
b) Is the field strength meter indicator reacting when you manually tune to a fm station?
c) Which measurements did you do so far? Tuning voltage? Power supply voltages?

Usually you would start with measuring all voltages according to the service manual.
The measurement points are indicated on the backside of the HF- und NF-mainboards.






These slides were originally prepared by our member Kurt (ksbsb) who posted them available in the download area download.tonbandforum.de/
I slightly edited them according to my measurements for the 9241.

Greetings
Reinhard

I think "Stimmnadel" is Abstimmanzeige, tuning indicator.

Try dict.leo.org but it is not a translator.
Leo is good for technical terms, not only English <--> German.
See the language flags, there are some more languages.
By the way, I invite you to write in English here.

Andreas, Admin

A newer version of the voltage measurement aid was posted by Kurt (ksbsb) some time ago:

92xx_SpgsVersorgung Messblatt_neu.pdf


regards
Reinhard

Hello aljecan,

the English translation is good.
Abstimmung means "field strength indicator" in this case.
"Tuning meter" is the "center tuning" indicator.

In all tests "Muting" must be switched off.

Did you measure the tuning voltage at test point A4?
It should read 3 V when the tuning wheel is rotated to the very left. And it should read 21.5 V when the tuning wheel is rotated to the very right.
Measuring point A2 should be 1.6 V DC.
Measurement point B3 should be 4 V DC.
Measurement point B8 should be 6 V DC.
Measurement point B4 should be 900 mV.
Please confirm these voltages before going to the next measurements and tests below.
If any of these voltages is wrong in your case, do not proceed. We have to fix it first.

You wrote that you connected a fm-signal generator with the fm antenna input jack and fed a signal, but the "Abstimmung" indicator did not move when you dialed to the carrier frequency of your fm-signal generator. For our information and further tests to come, please let us know the settings of the signal generator:

carrier frequency and rf-signal amplitude
modulation depth (deviation)
and modulation frequency.

You probably also have a 20 MHz oscilloscope (or even wider bandwidth).
If the tuning voltages at both ends of the fm-tuning scale measured correctly (3V and 21,5 V, which I asked you before), you should then check, if you obtain an IF-output from the FM-front end.

Test of IF-output from FM-tuner (FM-front end/mixer):
In a first step you need to confirm that you have no interruption between the FM-antenna input jack at the chassis-backside and the 75 Ohm coax antenna plug that connects through the little balun box at the FM-tuner box. Measure low resistance of the center conductor of the coax input jack to the center conductor of the coax-output plug of the little balun box that attaches to the tuner box. Sometimes it happens that the center conductor of the coax cable is broken inside the little balun box or the ground shielding wires from the coax cable make a short to the center conductor of the coax cable inside the balun box. To avoid this possibility, you can directly connect the fm-signal generator to the coax input jack of the fm-tuner box.

For further testing the FM-Tuner box you insert the box correctly again into the receiver and connect it via the balun box and the attached coax cable with the FM-antenna input jack.
Then you attach the (20 MHz or higher) oscilloscope to measurement point A2 (exit of FM-front end/mixer) via 1:1 AC coupling, oscilloscope ground to the fm-tuner box metal shield.
You feed a RF-signal at 96 MHz into the FM-antenna jack with 2-3 mV rf voltage, no modulation.
You tune the 9240 to the rf-frequency of the signal generator (96 MHz) and slowly left and right of it (back and forth) and watch out if you can see anywhere the 10.7 MHz sinus on the oscilloscope. For that you may need to switch the oscilloscope to high sensitivity (5-20 mV/Div). Slowly tune through the frequency band where you would expect to receive the signal generator signal.

If you can observe the IF (10.7 MHz), the front end / mixer is ok and the defect is in the IF-amp section.
If you cannot observe the IF, the IF-amp section shall be tested in addition.

Test of IF-amp/demodulator section:
You remove the FM-tuner box from the receiver and connect the FM-signal generator via a 20 pF ceramic capacitor with measurement point A2 on the main board. Ground of the signal generator shall be connected with one of the pins 1/3/7/15 (they are all = ground) of the IF-amplifier box in the receiver.
Switch the FM-signal generator to 10.70 MHz carrier frequency, rf-output voltage 50 mV and fm-modulate with 1 kHz at 40 kHz deviation.
Connect the oscilloscope to pin 14 of the IF-amplifier box, that is the output of the if-amplifier/demodulator. Ground of oscilloscope to be connecet with ground of the IF-amplifier box.
You should see the 1 kHz sinus signal on the oscilloscope.

At this point, let's see what you can find out. Further tests depend on your measurement results.

Best Regards
Reinhard

Hello aljecan,

Take all the time you need - no hurry!

When you tune into a station, is the frequency you dialed right at the stations's transmitted frequency?

Measuring point A2 is within tolerance.
Measuring point B3: Your voltage seems too low as a result of low rf field strength level arriving at the IF-amp box. The voltage as such is therefore allright (shall be 1...4V DC). It is about 1 V if there is no/too little field strength or poor or no reception. It is only 3 to 4 V if a strong signal is received.
Measurement Point B8 might be still within tolerance.
Measurement Point B4 is close to 2 V, which is ok, if there is no station received/no signal.

It looks from the measured voltages that
a) the IF level reaching the IF-amp box is too low, or
b) that something in the IF-amp box is faulty.

If you have a second (spare) IF-amp box, you could swap them and see, if you have then normal reception. That means the IF-box is defective. Or you still don't have normal reception, that means that the defect is in the signal path before the IF-box, as for example, the tuner box output or the dirst (entry) transistor in the tuner box has become weak.

If you have no spare IF-box to try, you must find out, if you have sufficient IF-level at Measuring Point A2, when tuned to a strong station (or from a signal generator). If there is not enough IF-level, the defect must be already before the IF-box.
If, however, the IF-level at Measuring Point A2 is within the normal range, the defect must be inside of the IF-box.

Proceed as follows:
If the antenna /coax-cable connection from the antenna input of the receiver to the tuner box has been checked and is ok,....
...insert the tuner box correctly into the receiver and connect it via the balun box and the attached coax cable with the FM-antenna input jack.

Attach the (20 MHz or higher) oscilloscope to Measuring Point A2 via coax-cable and 1:1 AC coupling. Attach the oscilloscope ground to the fm-tuner box metal shield.
Feed an unmodulated 96 MHz-signal into the FM-antenna jack with 2-3 mV(rms) level.
Tune the 9240 receiver to the rf-frequency of the signal generator to 96 MHz and slowly left and right of it (back and forth) and watch out if you can see anywhere the 10.7 MHz sinus on the oscilloscope. For that you may need to switch the oscilloscope to high sensitivity (5-20 mV/Div). Slowly tune through the frequency band where you would expect to receive the signal generator signal.

The IF- signal to be measured at Measuring Point A2 shall be roughly 50 mV(rms) at 10,7 MHz under these test conditions.
If you cannot observe the IF signal at Measuring Point A2 or if it much weaker than expected, the output stage of the TUNER/Mixer box may be faulty or the FM-input transistor in the FM-front end became weak.

Let's see what you find.

Best Regards
Reinhard

Hello aljecan,

I sent you the schematics with the parts values.

I am sorry, that you lack the required experience/knowledge to perform the necessary measurements. In such case you should look for somebody who can do it. Unfortunately, several defective parts could cause the symptoms you described. Therefore, the electrical unit has to be found first (fm tuner box or if-amp box), which is causing the problem. The measurements I suggested were geared to that question.

Often a request comes "tell me the part that I shall replace." But don't ask me to measure.
Unfortunately that is not going to work, not here and not in most of the other cases. Sorry.

Best Regards
Reinhard