Grundig satellit 2100 silent bands

[iceman303]

Hello friends. I have a satellit 2100, that is working except for the lw, mw, sw1 and sw2 bands. All bands are silent, I transmitted a small signal near the radio on different frequencies and there is no reception on these bands. It seems like the circuit ( t11 ) is not oscillating. I checked the voltages on t10, t11, and t12, as can be seen on the image. Those are the voltages I got. I don't know if t11 collector voltage is ok. I didn't find any open or shorted coupling caps. I'm not sure what else can I do, due to my limited experience. What should I do, or look for in this situation? Any help is very appreciated.

Thanks,

Joao G.

[frsimen]

Hello Joao,

The circuits that you have posted have the voltages and where they should be measured marked on them - they are marked in red. Your measurements have been made from a different reference point.

You will find it easier to fault find if you use the same measuring points as used by Grundig and it will be easier for others to help you then.

Paula

[iceman303]

Hello Paula. Thanks for the advice. How should I measure the voltages? Where do I place the multimeter probes? I'm not familiar with this method. What should the reference point be? If you can give me an example, that'd be great. thanks in advance.

[iceman303]

I figured out how to measure voltages like Paula said. I have measured the voltages according to the grundig service manual, on t10, t12, and t13 and they match closely to the stated values.

[ronbryan]

Missing wavebands on Grundig transistor radios is often due to poor contacts in the band selector switches. The design means that selection of a waveband relies on numerous series connections between the switches, so that a couple of dirty contacts can cause complete loss of many bands. Switch cleaner applied sparingly followed by repeated operation of the switches may restore correct operation.

Ron

[iceman303]

Hello Ron. Thanks for your sugestion. It makes sense. I've checked the switches / contacts though, and they all operate correctly. It happens on all lower bands ( 4 separate switches ) , which makes me think it is something common to all 4.
Thanks again Ron. I will keep testing.

[WaveyDipole]

The 'Ariel' as well as the SW3-10 switches might also be a common factor for all of these bands. Make sure to also give both of them a good clean. Since voltages around T10, T11 and T12 appear to be Ok, I would second ronbryan's comment about the switch contacts. If the radio hasn't been used for a long time, the switches may need to be worked a few times to get them going.

[agardiner]

Are the SW3-10 bands working? If so, then I would also suspect the switches before diving in too deeply.

[iceman303]

The SW3-10 bands are working. I tried cleaning the switches and working them for some time but so far no results. I do agree it might be ( and seems ) a switch problem. I tried transmitting a 1khz modulated signal near the external antenna ( with external antenna switch on ) on mw (1.5mhz), sw1 (3mhz), and sw2 (4.5mhz), and I get a faint signal with no audio on some parts of the band near the corresponding frequency ( in a broad way ). Thank you all for the help so far. Very appreciated. I will continue testing.

[frsimen]

You can check that the switches are making good contact with by using your multimeter. The resistance of a good contact should be well under 1 ohm plus the resistance of the test leads.

Another easy thing to do is to check that the local oscillator is working. You mentioned that you were suspicious of that in your original post. Switch the Grundig to MW and tune to around 600kHz. You will need another MW radio which you place near to the Grundig and tune to a frequency 460kHz higher (1060kHz or thereabouts). If the Grundig's local oscillator is working, you should hear the signal as you tune the Grundig around the 600kHz region.

This Grundig model has a complex arrangement for tuning on the LW,MW, SW1 and SW2 bands. The local oscillator and the aerial tuned circuits are tuned by a variable capacitor. The stage between the RF amplifier and the mixer is permeability tuned (described in the manual as a variometer). To work properly, it relies on everything tuning in step. If there is some sort of mechanical failure, the variometer may not be tuning and that will lead to very poor sensitivity. If the switches are good and the local oscillator is running, that would be the next area to investigate.

Paula

[iceman303]

Hello Paula. Thanks for your advice. I have tested all the connections of the relevant switches with the multimeter in continuity test, and they all seem ok so far. I also tried checking for local oscillator with another radio ( a akai am/fm receiver, very close to it and with a small wire as antenna on the am aerial and placed near the grundig ) and I did not receive anything on it. I tried this a few times. I did some testing on the variometer ( inductors and the variable capacitor ), maybe some wires could have been broken in transport, but those seem ok too, continuity tested, and the capacitor with capacitance meter. Just in case it might be useful, I have a multimeter, a frequency meter, a hf radio with am (1.5mhz - 30mhz), and an oscilloscope. How should I proceed next?
Thanks again for your help.

[Cathovisor]

Originally Posted by agardiner

Are the SW3-10 bands working? If so, then I would also suspect the switches before diving in too deeply.

On SW3-10 the signals are passed with an IF of 2.46MHz through a second mixer stage with a LO of 2MHz to be amplified by the AM IF strip used for L/M/K1/K2 so I'd be looking at the frequency changer. These sets are plagued with those grey-bodied Telefunken transistors that go low gain or even o/c - I had a 2100 in for repair where this occurred on the second mixer/oscillator transistor rendering it dead.

[agardiner]

As you have a good complement of test equipment, and given your tests with another radio, I would now want to confirm if the local oscillator was working in the affected modes. Try measuring it with your frequency counter or scope. Your previous tests suggest that it may not be oscillating. If that is the case, then replace the oscillator transistor as a next step, as they are prone to going low gain.

[frsimen]

As has been suggested above, it could be the transistor. Before changing it, do the oscilloscope check as described by Adrian - use a X10 probe to avoid shifting the frequency if the oscillator is working. That will probably confirm that the oscillator is not working.

One other check should be made. Check the resistance across C3. It should measure open circuit. If you measure a low resistance or short circuit, the vanes of the capacitor may be shorting together, or there may be something causing a short between the vanes and the capacitor frame. That will also stop the local oscillator.

Paula

[iceman303]

Hello. I did some more testing. I probed the oscillator transistor ( t11 ) on it's emitter and collector, and also the if transistor ( t12 ) on it's emitter, and also at the if output, on c431, and theres is no oscillation. I also tried probing t17 at the base and collector, and also no oscillation. I switched to a working shortwave band, and when probing t17 at the base and collector, I can see a sinewave, and when I tune into a station the sinewave increases and is modulated. The c3 capacitor ( that is connected to q2 ) measures 178 ohms to ground. I disconnected it from the circuit to measure. It seems like the circuit is not oscillating. One detail, is that, a few days ago, I thought it was not oscillating, and took t11 out and put in a bf494 ( I don't have any bf240 transistors ) in it's place, but it made no difference. But I might have done something wrong. I will do some testing tomorrow. Thanks.

[agardiner]

If I understand your last post correctly, you measured 178 ohm across C3 when out of circuit? If so, then it is faulty and should be replaced.

[frsimen]

I don't know what type of variable capacitor C3 is. If it is a polyvaricon type, then replacement is the only option.

Often Grundig use air spaced variables in their radios. If C3 is that type, have a good look at it for shorting vanes, debris between the vanes, whiskery growths across the insulators etc. If there is anything like that present, remove it and you should find that C3 measures open circuit with the test meter. Also if there is a ferrite bead located on the connecting terminals, make sure it isn't touching the frame of the variable capacitor.

If the wire connecting C3 to switch Q2 is screened, disconnect it at the C3 end as the wire itself could be the source of the trouble.

As another check, the local oscillator should work with C3 disconnected. It will be operating in the 2MHz region with MW selected, but will allow you to confirm that there is no other fault in that area.

Paula

[iceman303]

Hello friends. Adrian, yes, c3 measures 178 ohms out of circuit. I measured from the capacitor terminal to a nearby ground, since the other side of c3 is connected to ground.
The other capacitor, c2, ( which I think is part of the aerial circuit ), does measure open circuit. Both capacitors ( c2 and c3 ) are air spaced. I also tried disconnecting c3 from the switch q2, and check for oscillation, like Paula advised, but still there is no oscillation.
I did check again, with oscilloscope, and without the capacitor, there is oscillation at t11 emitter, and it's frequency changes according to the band choosen. But it still sounds quiet in reception, on all bands. I will continue testing and troubleshooting.
Thanks, and wishes of a great weekend.

[frsimen]

That sounds like progress.

If you can connect your oscilloscope probe in the X1 position to switch q2, with the radio set to MW you should be able to adjust the main tuning to get reception at good volume (it might only be noise) at some point on the dial. You should also see the oscillation on the oscilloscope. The oscillator will be running at too high a frequency for proper reception with C3 disconnected.

You need to concentrate on sorting out what is wrong with C3. Perhaps there is some contamination on the insulators or conductive dust between the vanes. Check that C2 hasn't got the same problem while you are working in that area. Reception will be rather poor if that has a similar issue. You will need to disconnect the wire from switch q11 before you can check C2.

Once you have resolved any issues with C2 and C3, you should find that the radio is working again unless there are more faults.

Paula

[iceman303]

Hello Paula. I connected the probe in x1 to q2, in mw, and the other different bands, and adjusted the main tuning, and there was a small oscillation that peaked when tuned to a part of the band. the signal is small and was more noticeable on sw1 and sw1, but also on lw, and mw. With c3 disconnected from the circuit, I replaced it with a small variable capacitor ( 150pf ), and I was able to receive some stations ( morse, rtty, etc ), on both sw1 and sw2. I also received a portuguese station on medium wave. I did not receive any stations on lw, but this band only opens at night for dx reception. It looks like the problem is solved. I will do some more testing to check for any other details I might have missed. I will later carefully remove the capacitor from the radio, and will check it, and try to find what's the problem with it, hopefully I will be able to solve it, and get the capacitor working. Many thanks everyone for all the help. It's very appreciated. I will try to fix the capacitor and later post my results.