Grundig Satellit 500 Service Manual
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According to the service manual with P/N 72010-711.31 - Printed in Germany 1189, the design uses a set of diode bridges to set between the International, Professional and Italian versions.
According to the service manual, the Test Mode also shows the current Bridge Diodes setup corresponding to the model version. To invoke the Test Mode, turn off the radio, type in the code 050251, press STORE to see the version, then press STORE again to see the Diodes Bridges.
The voltage at the outputs can be corrected in two ways. The easier way is to connect a 24-33 kohm resistor from each output (pins 7and 8) to ground. If you don't have the service manual, the correct points are positive pins of electrolytic capacitors C825 and C826. These capacitors can be found next to the larger shielded box on the RF board, on the side close to the loudspeaker. After installing these resistors the suppression of the unwanted sideband improved in my receiver from 14 dB to 20-26 dB, and I think the distortion is reduced too.
The unwanted sideband rejection can be further improved, but for this the service manual, a signal source (signal generator or a transmitter with clean carrier) and an AC voltage meter or oscilloscope is needed. The procedure is balancing the summing resistors after the audio phase shift circuits. Resistors in question are CR834/CR832 for LSB and CR833/CR831 for USB.
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If you don't have the service manual, the correct points are positive pins ofelectrolytic capacitors C825 and C826. These capacitors can be found next to thelarger shielded box on the RF board, on the side close to the loudspeaker. Afterinstalling these resistors suppression of the unwanted sideband improved in myreceiver from 14 dB to 20-26 dB, and I think the distortion is reduced too. Somehints for opening: the best screwdriver is Pozidrive #1. Ordinary Phillips doesnot fit well, and the screws are quite tight for the first few times to unscrew.The back cover should be lifted at the bottom side, there are plastic hooks atthe top side. The RF board can be removed completely after unscrewing the 5screws and unplugging all connectors. There MAY be an extra capacitor solderedbetween the RF board and the shield of the processor unit, in the vicinity ofthe antenna socket. It must be then unsoldered too. The board is manufacturedusing surface mount components, so certain caution and fine tipped solderingiron is necessary. The procedure should be undertaken only if you are sure thatyour detector is defective too. This can be determined by viewing the suppressedsideband signal of about 500 Hz with an oscilloscope connected to line output,it must be severely distorted. Another symptom is bad suppression of theunwanted sideband. At frequencies between 50 and 200 Hz there is another reasonfor the distortion of the beat signal: feedback from audio stages to thefrequency of the first mixer oscillator. This can be improved by connecting a2000 microfarad or larger capacitor from the AM +3.5 V to ground (pin 11 inconnector A). The detector can be switched to selectable sideband synchronousmode also, but here rather strong phase noise of local oscillators createsclearly audible background (about 20 dB below audio). Also, the shieldedoscillators exhibit strong microphone effect, resulting in audio feedback athigher volume. To achieve this mode, pin 3 of connector C on the RF board can beconnected to ground via about 1 kohm resistor and a switch. This resistor isuseful only for avoiding extra interference from processor, also to avoid shortsin case of errors. For receiving normal SSB transmissions this connection shouldbe broken. The unwanted sideband rejection can be further improved, but for thisthe service manual, a signal source (signal generator or a transmitter withclean carrier) and an AC voltage meter or oscilloscope is needed. The procedureis balancing the summing resistors after the audio phase shift circuits.Resistors in question are CR834/CR832 for LSB and CR833/CR831 for USB. Theresults on my receiver are following (the frequency of the best suppressiondepends on actual component values in the phase shifters and is probablydifferent for other receivers): Freq. [kHz] USB [dB] LSB [dB] 0.2 15 14 0.5 1615 1.0 26 24 1.6 48 42 2.0 36 36 2.5 29 28 3.0 25 24 3.6 22 20 For properbalance CR834 was reduced by 10% and CR833 by 20%, but I am sure this isdifferent on each sample. The best suppression value says also something aboutthe distortion. 2b1af7f3a8