Soviet East German Radio

[Nowhere-Man]

I should clarify diagnostics is currently a weak area for me. Diagnostics is maybe the core aspect of most radio forums. Most people identify the source of a problem with test equipment and hopefully repair the set. There are other aspects, though, such as rebuilds or schematics or construction. However diagnostics is where I think I need a bit of time to get more organised.
Fortunately I try to do my research. The Saalburg 1964 GDR radio is one I shelved months ago as being too advanced. I am now taking another look to see why only FM is working. I now know the Oscillator voltage is missing from my mixer valve at the triode anode. The hexode anode is fine. I have traced accounts from others who have encountered the same problem. Breaks in the oscillator coils are the main observation. I now started cleaning this area of the circuit so I can see better as the set is very dirty. Last night I located the oscillator feed resistor which helps. Access to the piano key contact is not possible yet unless I opt to remove the PCB. I did consider the mixer valve itself may simply be defective and it's the only one where the voltage is missing. I should point out there is an FM oscillator apart and that clearly is OK. Having a schematic in German with no commentary makes this more challenging.

[pwdrive]

Fault finding can be as easy or hard as you want to make it, I served my time as a R&TV trouble shooter, mainly valved stuff, current flows in a loop, V/IR etc it's not difficult but sometimes looking at schematics can be, especially if there's a lot of switch contacts involved such as band change switchery, sometimes pays to print out a copy and highlight the part of the circuit you're trying to analyze with a marker pen or pencil and tick the various circuit branches/components off as they are checked.

Missing voltage problems should be easy to diagnose, 10 mins tops for most faults.

A multimeter is a good fault finding tool, so is a 'scope, if one had to be ditched forever then I would keep the 'scope, others folks may differ.

Keep at it.

Lawrence.

[Refugee]

Switches are a pain if you are not good at reading circuit diagrams.
I took a challenge and won against a big scope.
Only about a third of the timebase ranges were working and I had to find out where all the wires from the switches went to and trace it through.
Once I had found the wrong signal at each end of the switching system it was an easy fix.
It took a couple of hours to sort out the search thru the switching and then a matter of minutes to find a faulty JFET and another half an hour digging out a spare.
The FET was socketed so I did not even have to warm up a soldering iron.

[Nowhere-Man]

Here's a pretty closely related receiver. I have sought out a few accounts of other peoples' experiences with the East German radios. The person in the thread around this uploaded pic had had issues with the oscillator. He was seeking parts. I can't see any major problem yet with the oscillator circuit on my radio apart from one disconnected, fine coil wire which I re-soldered. I am not totally clear whether the actual valve can be at fault where you get no volts on the oscillator anode. I don't see why that isn't a possibility (faulty triode) but it is never mentioned. Therefore, I am gradually checking the circuit while cleaning with cotton buds. There is an enormous amount of grime so just getting all the wires and lugs clean and visible helps. I don't tend to rush ahead as I like to learn how the circuit has been put together at the same time.

[Murphyv310]

Hi.
The only way the valve would cause zero volts on the anode is a short from Anode to cathode and that is assuming the triode cathode is returned to chassis (ground) very very unlikely. If its an AC set (with mains transformer) then pulling the valve would give you supply on the anode connection in the unlikely scenario the valve was duff.
In normal practice (virtually all AM FM superhet valve sets) the anode will be connected to the Osc TX primary, the HT side of it will feed via a resistor around 10-39K ohm and back to the AM FM switching that will have HT contacts to cut the oscillator HT feed on FM.
There are some variations on the theme on some sets but they do follow similar circuitry.
My bet is the switch contacts dirty, broken or inadequate mechanical movement due to wear, dry soldered joints if the switch bank is soldered to a PCB or a simple O/C in the wiring unless the coil is still duff.

[Nowhere-Man]

I have to agree. I suspect something amiss with the pushbutton. One problem is this for me is a 20 year leap in technology. I've had little experience with FM. I am fine on rotary waveband circuits of the 50's era. If it becomes absolutely necessary I will remove the pcb and with great care. For now I seem to have the oscillator resistor identified. I will test the grid bias too. Cleaning helps to see the soldered points.

[Crackle]

Hi Nowhere man
Please can you correctly identify the Saalburg model number, it would be very useful for anyone who may, in the future, be looking for help with one. It would also make it easier for anyone on here who wishes to to follow what you are doing.
It would also be very useful to know where you found the service information.
Thanks
Mike

[Nowhere-Man]

Sorry I didn't notice this before. You are right to have asked the question as the only guy who seemed to have posted a success story is Howard Craven. There is no solid information on this set in English but I hope to run a feature on this radio. To give an example the low voltage on one of the anodes led some to get confused because 64 volts isn't at al usual. I will give you the ref number later on. I am not going to pull the PCB off yet till I am more clued up on the proceedure. I did find the odd account where repair became very stressful (wires coming off and so forth). I am learning just a little German to prepare and I musty double check grid bias on the Hexode am mixer and oscillator.

[Nowhere-Man]

I am not at home at the moment and it's the last Chritmas rush scenario. So I'll add information later. There are slight differences in Saalburg model numbers but I imagine no major circuit difference. The stringing mechamism would clearly be no picnic unless you really take very detailed notes and photos. I should add that most people who posted for advice in the past had oscillator voltage issues or assumded low anode voltage was part of the problem. All my voltages are A OK except the Triode anode of the AM Hexode which is dead. I will check any short to ground where I can and only remove the PCB if I need better access. However Christmas has stopped me in my tracks for now.

[Nowhere-Man]

The schematic I have is for the 5170 and they can be tricky to find. The valves are ECH81 mixer, EC85 double triode and FM oscillator. The EBF89 double diode is reputed to run on low voltage and the EABC80 I know will run at 60 odd volts. The EL84 is the output valve. I'm not sure if the Mullard and German valves of the same names are identical. After some basic work I am now getting mind-boggling audio quality that beats anything modern. It is still only working on FM and the ECH81 triode anode is still dormant. My guess is a capaswitch problem as I got no voltage on the oscillator feed resistor but HT passes via a piano key knob (39 I think). Tonight I was weighing up the removal of the PCB and find the switches have tabs soldered to the boards at chassis potential.
Another thing I should add is this set really carries some voltage.
If I ease out the board I can change any wax capacitors and I can test the tracks. It is honestly a bit over my tlevel to be honest and is in the Philips range of repair. That includes the dial chord. However I can persevere and then share anything I discover. And let me repeat the sound on this is awesome. I have never heard such a quality of audio on any other radio to date.