Quote:
Originally Posted by muttley1984
I have been looking at the circuit diagram and still cant get my head around how the 'piano keys' switch contacts work. Without this I dont think I have much chance of tracing cables. I will spend a bit more time trying to figure this out but any help is much appreciated.
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They look complicated but reasonably simple to work out the basics but not so easy for me to put down in words but here goes anyways....So far as I can tell so far based on this schematic:
http://85.144.192.2/nvhr/Braun_TS2.pdf
Looking at the switch drawing on the schematic sheet all the contacts are numbered (1,2,3,4 etc) for each section (A,B,C,D etc) Each section corresponds to a function, the switch contact numbers along with their A,B,C,D etc designations are all to be found in the schematics drawn circuit, it's easy to miss some of them but after the following descriptions you should be able to find them all if you haven't done so already. The switch bank is shown in the out position, eg: no switch buttons depressed, if a L (long wave) M (medium wave) or K (short wave) button is pressed then the contact bars for the switches in section A will remain as shown and the contact bars for the switches in the selected section will move upwards (as viewed in the switch drawing)
Section A: The switches are shown in the AM position (L,M & K) in that position the primary of the FM IF transformer (SP22) is shorted out by switch contacts A8 & A9 and the grid voltage for the tuning indicator is sourced from the AM AGC line via switch contacts A5 & A6. When UK (VHF/FM) is selected the contact bars for both A section switches move upwards, this releases the short across the primary of the FM IF transformer (SP22) because switch contacts A8 and A9 are no longer connected by the contact bar, and the voltage for the grid of the tuning indicator is now sourced from the FM demodulators -ve output circuit via switch contacts A5 & A4.
Section B: PH (phono) When this section is selected the receivers audio amplifier input is connected to the record players pickup output circuit via switch contacts B2 & B1, contacts B8 & B9 are also disconnected from each other, this disconnects the HT feed to the IF amplifier valve (the 2nd EF89) and also to the tuning indicator valve, when PH is not selected the input circuit of the audio amplifier is connected to the receivers demodulator circuits via switch contacts B2 & B3, the relevant demodulator output being selected by the position of switch A via switch contacts A5 & A6 for AM or via switch contacts A5 & A4 for FM.
Section C: L (long wave) When this section is selected the long wave RF coil (SP11) is switched in via switch contacts C3 & C4, the tap on that coil is connected to the medium wave coil (SP9/10) and the medium wave trimmer (C27) The long wave coil connects to the grid circuit of the mixer via switch contacts G2 & G3 and switch contacts K2 & K3
The oscillator inductance for long wave is made up of coils SP13 & SP14 connected in series, SP13 is the medium wave oscillator coil.
Section D & E: Fa-Ru....Not entirely sure yet what this sections function is, I tried Google translate based on what's in here:
http://www.radiodesign.de/museum/bil...super99bda.pdf
but I can't quite make sense of it, maybe someone else can, anyways from the switch descriptions so far it isn't difficult to figure out what connects with what when the button is out or when it's depressed. Unselected it introduces a +ve voltage to the FM demodulators -ve output rail that controls the gain of the last IF amplifier on FM (via its suppressor grid) and which also supplies the grid voltage for the tuning indicator on FM via switch contacts D8 & D9, contacts D8 & D9 can only supply this +ve voltage when UK (FM) is selected due to switch contacts H8 & H7, also switch connections E2 & E3 connect the antenna input circuit to a series combination of the short wave wave antenna winding of SP8 and the medium wave antenna winding of SP9/10. When the function is selected, the antenna input circuit is only connected to the short wave antenna winding of SP8 via switch contacts E2 & E1 and the +ve voltage mentioned above is disconnected.
Section F: M (medium wave) When this is selected, contacts F8 & F7 short out the longwave oscillator coil (SP14) The medium wave oscillator coil (SP13) is the only one left in circuit due to the action of switch contacts G8 & G9.
Section G: K (short wave) When selected, switch contacts G2 & G1 connect the short wave RF coil (SP8) into circuit, switch contacts G8 & G7 connect the short wave oscillator coil (SP12) into circuit.
Section H & K: UK (VHF/FM) When selected, switch contacts H8 & H7 connects HT to the VHF/FM tuner head, switch contacts K2 & K1 connects the output of the 1st FM IF amplifier transformer to the grid circuit of the mixer which also serves as the 2nd FM IF amplifier when the UK (VHF/FM) function is selected......Phew.
I hope this might be of some use.
Guilty as charged if there's any errors.
Lawrence.