grundig: Satellit 650 motor drive function not working properly

A Grundig Satellit 650 works perfectly from most standpoints; all bands work fine in terms of manual tuning and the resultant audio quality. However on AM, when either a frequency is inputed using the keypad, or, the large tuning knob is used - in other words in motorised mode - the motor drive doesn't work properly. Instead of moving directly to the desired station in the case of keypad input, or 'inching' its way along when using the large tuning knob, it always moves from right to left in a jump of about 2cm each time until it ends up on the far left of the scale. It never moves to the right, and it always moves in these 2cm jumps.

Any ideas what is wrong? Thanks.

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The motorized Drive has some special Behaviors by Design:

- When motorized is turned on, and a specific Frequency is selected, by quickly turning the Dial, the digital Display shows the actual Frequency immedeately, but the Motor waits, until Frequency Change has stopped, and then schould move in one Move to the selected Frequency.

- The motorized Drive is of limited Precisition. It only compares the Position of a Potentiometer( which is mounted at the Tuning Capacitor ) with the actual Oscillator Frequency by use of a fixed Lookup Table.

- There is a Calibration Procedure for final Adjustment, which is to be used, if the Motor Drive works correctly, but is always a bit off Peak.

- It is quite normal, that when moving the Dial slowly, the Motor is driven in steps, of typical 2 to 5 mm.

- to start with tests, i would recommend, to select AM 550khz-1600khz Range, turn Motor off, move analog Dial to 900 khz, set frequency to 1000 khz via Keypad, and then turn Motor on. Motor schould move to 1000khz. repeat with 1100 khz.

Hope this helps.

best Regards,

Henning

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Hi,

Thanks for the overview of how the motorized drive works.

As I have already explained, it does not move to any set frequency, it will only travel from right to left in 2cm steps when a move is initiated. It will not travel to the right, it always end up at the far left hand side.

Where do I go from here?

Best Regards,

Steve

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Hi, Steve,

i have some more Questions, to get an Idea, of what might be wrong. I have the same Radio in working Condition.

Has the motorized Tuning worked before, and then failed by itself? Or was a Repair done, and afterwards the Radio showed this Problem? Or did You get the Radio with this Problem?

I also will prepare some electrical Tests and Measurements, which will take some time.

Best Regards,

Henning

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Hi Henning,

I bought it with this problem. I have fixed other problems, mainly by going over poor solder joints on boards, cleaning switches etc, but this problem remains. Otherwise, everything seems to work fine, no issues that I have noticed.

Thanks for your ongoing help and support, appreciated.

Steve

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Hi, Steve, next step would be, to test, if the Position of the Varicap is visible to the Microcomputer. For this, there is a Potentiometer moved by the Variable Capacitor.

One End is at Ground, the other End schould read apx 4 Volts, and the Wiper schould read something in between, representing the Position.

This Voltage is used by the Microcomputer to find out, if Motor is to be moved right or left to meet the required Position, as given by the selected Frequency.

there is also a complete Description of all Functions of this Radio available on the Internet, but i think, only in German. Maybe You can find it in English also, or maybe Google Translator can help.

best Regards,

Henning

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Thanks Henning,

Are you able to identify where this particular pot is? Note, I am an electronics engineer, I have been repairing vintage equipment for decades, and I have the Grundig stripped down to the main chassis (front and back removed) and am reasonably familiar with the layout of things, but Not sure where that pot is.  Thanks!

Steve

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Hi, Steve,

this Pot is mounted on the right side of the Variable Capacitor ( see from back of Radio ), or in other words, it is part of the Variable Capacitor. 

Best Regards,

Henning

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Hi Henning,

Thanks, yes I have located the pot now.  The voltage at the top of the pot is 3.5V and the slider varies between 3.5V and 0V depending on the position of the tuning capacitor.

Thanks so far!

Steve

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Hi, Steve,

as the Voltage at the Pot is marked with 4.1V in the Diagram, there is a Chance, that there is something wrong.

If You look at the Circuit Diagram, there are two Adjustment Pots ( they are propably Part of the "big" Pot ).

the Wipers of these are also fed into the A/D Converter, and there are Caps to Ground. Please check the Voltages and check, if the measured Voltages can be calcualted by Ohms Law, and everything makes sense.

If all looks OK, there might be something wrong with the A/D Converter. I am not an Expert with that.

Best Regards,

Henning

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Thanks Henning, I'll work along those lines.

Best Regards,

Steve.

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Hi Henning,

As an aside, the voltage on the main dial scale lamp is only 4.5V, but it is a 6/7V bulb. I'm wondering if there is a more general, low voltage problem somewhere - not necessarily related to the fault I'm looking for - but still in need of attention? May I ask, what voltage does your bulb read?

Do these sets suffer from power supply faults much?

Thanks,

Steve

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Hi, Steve,

please check Voltages at IC901 and 902, and verifiy, if You read 9,1 to 9,35 Volt, and 5V. Please check for required Tolerances at 5V as shown in Circuit Diagram. Correct Voltage is important for proper Function of the Microprocessor.

Please make shure, Your Meter is reading correct.

Hope this helps,

Best Regards,

Henning

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Hi Henning,

Thanks, I'll use a DVM to be sure and accurate.

Thanks again,

Steve

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Hi Henning,

IC901 voltage is 9.97V (10V later today)

IC902 voltage is 4.92V

Are those correct or problematic?

Best Regards,

Steve

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Hi, Steve,

i would think, this schould be OK for now.

Next, Please check the Voltages at the two Adjustment Pots, which are also fed into the A/D Converter.

( Post 10 )

Best Regards,

Henning

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Hi Henning,

Thanks for your help. I've got about as far as I can go with my somewhat limited ability to repair this radio. It will be for someone else to fix.

Thanks again,

Steve

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Dear all,

please note this recently posted forum article from Rainer Reiche (in German) where the adjustment for the motorized preselector of the Grundig Satellit 650 is described.

Here an English version:

Grundig Satellit 650 - preselector performs incorrectly

The Satellit 650 automatically adjusts the rf antenna and intermediate circuits after switching on the automatic function. This works somewhat poorly with my device, which I bought in 2014. In principle, it will follow, but generally it tunes too high, which becomes annoying over time, especially for SW reception.

Steve Rowley and Henning Oelkers had already discussed this in a forum post that gave the decision for my own investigations.

My adjustment procedure: There is a potentiometer (R830) mounted at the back of the 3-gang variable capacitor and coupled with it's shaft. The position (voltage level) of the pot is converted by an ADC, the ADC0833, via CH0. There are also two 2 reference voltages. The lower one is set via R829 and sent to CH1, the upper one is sent via R827 to the reference voltage input of the ADC (pin 9).

Before I started, I noted the values. These are in my set: R829 = 8 mV, R827 = 1.98 V. If you now increase Vref with R827, you will notice that the preselector will tune too low in frequency. By turning the pot back and forth (rocking) a few times, you can quickly get a good average between too high and too low.

With these settings, the automatic retuning works great on my device: R829 = 8 mV, R827 = 2.05 V. The voltage noted as 4.1 V in the circuit diagram was 4.05 V for my device, what one can accept. R827 and R829 are specially marked in the service instructions, unfortunately there are no adjustment instructions with it. The trimpots are easily accessible.

[Translation by BN]

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