Since I moved to Graz for university, I brought some speakers too, but my EL34 amp was too big and fragile to bring along. So I looked out for an old amplifier, because you can get them quite
cheap and they are easy to repair if needed. Fortunately a friend of mine had one at home which had a channel not working properly and the front panel led's not working. I first thought that the
amplifier IC is the problem, but it wasn't ! At the time I discovered I already had ordered a replacement IC. After taking a look at the proposed schematic of the amp IC in the datasheet, I ended
up checking two resistors that are in series with two caps I replaced earlier, because the dried out. And what do you know, one of these fucking resistors was bad. After I replaced it, everything
worked just fine.
The reason for the non working front panel led's was quite strange. There are two 7812 voltage regulators mounted at the bottom of the case for cooling. One of them had all three pins shorted together with a big blob of solder ! I've got no idea why something like this happend. Maybe it got to hot and the solder melted or somebody had already a "look" at it.
I replaced both of the regulators, because the are connected to the same rectifier and the other one might got damaged. The rectifier itself consisting of four diodes was also replaced as long with the filter cap. But still nothing worked. Somewhere 16.6V AC from the transformer were disappated.
After a closer inspection of the transformer and the boards attached to it, I found a fusistor, a fuse that normally acts like a resistor, but exceeding a certain amount of power it blows or gets high impedant. The latter happend. It had 2MOhm instead of 0.47 Ohm. After changing the fusistor, the aux power supply works now fine again.
The amplifier IC still needs to arrive from eBay, but it should arrive this week, so I can finally listen to some music, without headphones :D
My speakers are some Aiwa SX-780, which I bought for 10€ each. So I didn't bother that they aren't in good shape. I listend to some music with them as test before I moved flat and I found them to be ok.