Point taken, rechecked and remeasured anything I touched, and it all checks out.

That the amp sounded perfect for several minutes untill poof in my mind attests to a correct pre-amp job, else in my mind it would have sounded crap.

I left it on long enough also to mkae the idle current measurments. No fuses blow or anything like that.

And when I now measure the two pieces of what is left of that 470ohm resistor I have 54 volts over it. It leads me to suspect those largish resistors and that point-2-point network next to the large caps.

The caps themselves checkout, and that the rightside is getting correct voltages and is fine seems to indicate correct rectification and supplyvoltages exist. So my only though left is where the supply of power separates to the left and to the right side. and thats those jumbles of resistors.

Is that a sound deduction?

So two points:

1. I have a little issue with seeing certain colours , so decoding the values thereby deducing which resistor is which is hard

2. As I can't deduce which resistor is which i have a hard time applying the schematic to reality to understand how its all connected the way it is in reality.

From each terminal of the reservoir cap goes a wire to a point which is connected to another terminal with a resistor. This point is also connected witha resistor the the terminal point of the other polarity.

So from each point with a cable leading to the underside of the pre amp (one per side) each point is connected to both polarities of the reservior cap

...just with two different kinds resistors.Unsoldering them, they are off their spec (if I assume they are the resistors i belive they are , circled in yellow)

But not in such a way to cause 26 volt to become 54..

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I have studied these posts, ven though my issues are slightly different

/forum/imported-unmapped/beomaster-3000-type-2402---blows-fuses

But Can't realy find deviations in the Ohms.

Thanks.

OK,

Do you you have pictures of that board section?  If you can't read with accuracy the resistor values and we can't trust the schematic, can you at least read them from the pictures you have?

The resistors you circled in yellow seem to me drop down voltage resistors and you have them on both channels.

Are the resistors burned on both sides?  If yes then we must check the common power supply for problem.  

Hi,

Here are a few pictures, I will dismantle and measure each component.. trying to figure something out...

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Using Dillen's questions from the older BM3000 posts i linked to, i verified that the 3055's of the busted channel were toast.

If those became toast because the preamp blew or if the pre-amp blew because the 3055 blew is my question.... and what started it all  in anycase..

Measuring Also measuring from the power pins (front center across back corner) on the preamp board gives 50K on the working channel and 15k on the busted one.

But that is basically measuring the bustedness of the pre-amp , possibly not the cause of the cascade in the firstplace.

so im getting new 3055's and replacing the copopnents on the pre-amp.. but im realy cautions of the fact that i might not have found the root cause yet...

Im back with some news.

Replaced the 3055, but still nada... so i gathred that more of the pre-amp had blown... replaced TR59 and TR60 with temporary lover voltage transistors, just to see if I can get anything through headphones..

Voila!, the channel is now alive!

Two strange things though. On the previously dead channel I have 50Hz hum...  on the other channel perfect silence when volume is "0"

I read somewhere that it might be a decoupling cap thats gone open circuit... any other thoughts?

Also when trying to set the idle current i can't measure anything on any channel.. nada , zero? 

FM radio now working through headphones on both channels, 50hz hum in one, and no idle current what so ever on either channel... Rather not connect speakers until i understand whats going on with the idle current...

replace the two 1N4148 as well, disconnect the preamp and connect a sinus generator for testing the preamp.

Most 50Hz hum is caused by faulty caps in the powersupply. Does the 3000 have 2 separated power supplys?

Do you have 50Hz on every source?

Ralf

Hi Ralf,

Will replace the diodes tonight, lucky break i actually have a few.

Yes, the 50Hz is on every source. The filter/reservoir caps all changed. 

And no, the 3000 doesn't have separated powersupplies, The hum is produced from the one channel only and no difference is heard regardless of 220 or 240 setting.

I unfortunately do not have a sinus generator.

thanks!