[agardiner]

I am sure many of you will have at some point battled with a set that tests your skills and causes you frustration! Well, that was certainly the case for me with a Grundig Satellit 600 set.

This large heavyweight world receiver, complete with its leather case, originally came in for a routine repair; recap, turret tuner service and full alignment. Duly returned to the customer, he enjoyed it for only a week before it broke down. Initially it seemed that the internal power brick was the problem, as he continued to listen on batteries, but after around a hour, the sound became very distorted and then smoke started coming from the set! Thus it was dispatched back to me for further analysis.

It arrived well packaged, and looked fine. But when the chassis was removed from the set, it became obvious that the courier had been less than gentle. The speaker had torn away from the baffle board on two of its mounting posts. I carefully glued the speaker back in, but this proved to be premature; more on that in a bit. Starting with the power brick, I found a simple failed fuse. I powered the set up from my bench supply with a series current meter, to find that it was attempting to draw over 2 amps. No wonder it smoked!

The obvious suspect was the output transistors, an AC188K and AC187K pair. The PNP one was completely short circuit, so both were duly replaced. The set now drew around 150mA and the sound was back; but 150mA was still far too high. Before I could switch off, the current suddenly dropped to a more modest 35mA. Moving the amp PCB, caused the current to intermittently jump between the two states. Anyone who has worked on one of these sets will know how difficult it is to work on the amp PCB; there are lots of very tight wires running to it. A really good examination failed to turn up a faulty joint, so at this stage I decided to insert the current meter into the output transistors feed, in order to check/setup the quiescent current. This proved that the fault location was somewhere here, as the current kept jumping to the fault state as the PCB was moved. Trying to set the quiescent current demonstrated that the fault was the preset control itself, which was going open circuit. A replacement from a donor set brought stability to the current draw and allowed me to set the quiescent current to its 7.5mA level.

That should have been the end of the story, but this set had other plans. Disconnecting my bench speaker and reinserting the chassis into its case, resulted in no sound at all. Removing it again, and reconnecting the bench speaker; still no sound. I then tried injecting tone into the volume pot, which proved that the fault was once again the audio PCB. I removed and checked the two pre-amp transistors, both seemed OK, so I removed the output transistors to check them. They also tested fine, but only showed an hfe of around 9, so just in case they had been damaged by the intermittent current fault, I fitted replacements (gain of 120). As expected, no change. Out with the oscilloscope - the amp seemed to be working fine, so why no sound? Time for a gin and tonic to take a break from the frustration! On returning, I connected my bench speaker through a 1000uF cap directly to the output transistors - sound! Further careful checks under a magnifier revealed a hairline crack in the amp PCB - probably also caused with the transit damage. Hooray - this was duly repaired and the set once more reassembled.

No sound. This radio was determined to drive me to drink, so I obliged and poured a 2nd G&T! Removing the chassis again showed that one of the speaker wires (solid core) has broken from its connection due to all the pulling and pushing around. I remade it and carefully checked all the others. Once again I reassembled the chassis and once again I had problems. There was sound this time, but it was terrible! Really distorted and nasty. Remember that premature gluing? After proving the electronics were still OK, I carefully cut out the speaker to find that it too had succumbed to the couriers heavy hand - the small front tweeter had completely broken apart and had lodged into the main speakers cone. Fortunately I had a spare from another set which I was able to substitute, and at long last (and a third G&T) the Grundig was working properly once more.

These really are fantastic sets when they work properly. It is no wonder that they are still enjoyed. The owner of this one is now going to make the journey to collect his prize; we are not risking it via other means!