Soviet East German Radio

[Nowhere-Man]

Oh, Crackle, I should have said the chassis and shaft knobs have been removed ages ago. Speaker wires were just twisted on when testing. All the knobs are bagged. I don't have to worry about that for now, just want to work on the board and switch mech.

[Refugee]

Can you see the track side of the board?
If you can use a meter on low ohms to check between the soldered ends of the offending resistor and the track itself. The solder flux will have been made from coal tar and can often be slightly corrosive causing an invisible gap in the track.

[Nowhere-Man]

I may abort. I got the board free although to remove it I'd need to clip a few wires otherwise they would pull off. The tuner would have to be desoldered. Sure, with care, it's doable and it allows me to tidy up the board and better change the caps.
However, at this stage I can easily put it back together and no harm done. Then when I gain more experience I can resume the project.
Refugee, I will test the track a bit more as it's obvious it's a bit aged. I do have full access to the tracks but the wiring under the waveband knobs is out of range. You can see wires disappear below between the mech and upper board.
Not much else to add.

[Crackle]

I think you have made the correct decision to not dismantle it further.

Wave change push buttons can create a lot of stress on the printed circuit when they are operated, particularly with piano types with their long levers. I have often had problems where the constant movement of the buttons has cracked solder joints where the push button connection posts are soldered on the board.
If you solder it all back together properly, spray switch cleaner into the switch contacts, check the resistor R12 (suggested long ago) and test the radio before you put the chassis back in the cabinet, I wonder if it may even work.

Mike

[Murphyv310]

Can you see the track side of the board?
If you can use a meter on low ohms to check between the soldered ends of the offending resistor and the track itself. The solder flux will have been made from coal tar and can often be slightly corrosive causing an invisible gap in the track.

Never heard of coal tar flux, rosin fluxes derive from pine trees and are then refined.

[Refugee]

You are right about the pine trees.
The huge amount of flux needed once the industry got going made it cheaper to get it from else where as demand rose.
The refining was not as good as it is now.

[Nowhere-Man]

Crackle, my earlier posts show R12 was tested with the result there was no HT voltage. Continuity showed a connection to ECH81 anode as it should be one side. The other side of R12 shows no supply to HT. Not even when pushing the knobs. I assumed a break in the switch but underestimated the gaining of access. Now I discovered a useful diagram you can see on Radio Museum. The Telefunken ECH81 is shown with R12 at 33K only between HT and Triode anode. The anode should pass 13 milliamps (in ref book) and voltage around 100 DC. Not sure about the black circles with digits but at a quick glance maybe current? The two smoothing condensers also show two paths - one centre tapped if I recall.
Yes, I am not going to dismantle the board. Refugees suggestion was solid enough. I can try and trace the board from the tracks and, yes, WD40 is worth a go.

[Nowhere-Man]

Was lucky to be able to fix my synth today which had gone dead. A bit of solderinng and all should be well. However I have hardly room to move on my boat and I keep losing tools. These radios are all over the place and it's gotten ridiculous.
I appreciate the tips been given so far which have helped. Maybe later I will post some pics.

[Murphyv310]

Hi.
Please could someone point to R12 on the layout... Pretty please

[Crackle]

Not 100% sure but I reckon it is this unmarked resistor, it looks like it is connected to pin 6 of the VHF push button.
   

Mike