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Old 6th February 2009, 10:20 AM   #1
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Default broken rb-1090

Bought this power amp 6 months ago for a cheap price as the previous owner had said it probably just needs a new fuse fitting inside.
I replaced 2 blown fuses on the left channel pcb, then fired it up. A little smoke (tiny bit from the left channel pcb but the fuses did not blow and now there is nothing on turn on, no life at all.

So after this, i decided to put it in the loft and forget about the money i had just wasted until now when i have got too much spare time (no work) i am deciding if i can fix it.

Does anyone know this amplifier or this sort of behaviour on a power amp and where to start?

Thank everyone for help in the past and i am in your debt which i will pass on when someone asks a question that i will know through your help.
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Old 6th February 2009, 10:59 AM   #2
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http://www.hifiengine.com/manuals/rotel/rb-1090.shtml
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Old 6th February 2009, 11:19 AM   #3
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Slightly increase the value of the NFB resistor and set the input stage resistor-to-ground at the same value. This increases the gain of the amp a little bit and inhibits its tendency to blow the rail fuses.
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Old 6th February 2009, 01:33 PM   #4
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http://www.audio-circuit.dk/

has got the ROTEL RB1090 Technical Manual, for free
Schematics
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Old 6th February 2009, 02:31 PM   #5
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I have opened the amp up and taken it to bits. There are 2 totally seperate pcb's one left channel and one right. Each one has 10 big transistors.
I was doing some continuity testing on each of the pcb's. On the left pcb, when i connect one mm probe to the back of the transistor and the other probe to each (one at a time) of the 3 pins, only the middle pin makes a beep (connection).
On the right pcb when i do the same, all 3 pins make a beep.
Surely this must be the problem? But because of my lack of knowledge, which one is faulty? Should a transistor make a beep on all 3 pins or just the middle one.
The transistors are as follows for each pcb;
sanken 2sc3264 (81y) 3 of
sanken 2sc3264 (76y)1 of
sanken 2sa1295 (80y)3 of
sanken 2sa1295 (780)1 of
SK c3263 (9 20)1 of
SK a1294 (9 20)1 of

Where would i easily buy these components? Maplins?
Thanks for your help.
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Old 6th February 2009, 02:47 PM   #6
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the back is usually connected to middle pin = collector
for power transistors
so beep from middle pin to back is okay

those with beep from back (or middle pin)
to the outer pins (1,3 =base,emitter)
might be shortcircuited, and defect

instead of testing with the BEEP
you may measure the resistance between pins

Here is an Instructions for testing transistor:
Transistor test using an analogue multimeter
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Old 6th February 2009, 03:05 PM   #7
lineup is offline lineup  Sweden
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Here you can find datasheets
to see what is the
B - base
C - collector
E - emitter
of the Sanken 2SC3264 and other
http://www.datasheetarchive.com/sear...pe=default&p=1

They are very good and big power transistors
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File Type: jpg sanken.jpg (17.7 KB, 347 views)
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Old 6th February 2009, 03:44 PM   #8
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Thanks for all your good advice so far.
I will test the transistors in an hour or so and then get back to you.
I do have to test them out of circuit? Or could i get away with testing without de-soldering?
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Old 6th February 2009, 04:36 PM   #9
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Done testing the transistors and yes one channel has deinitely shot it. All 10 transistors have gone.
Where can i buy these? What makes all the transistors one one channel blow? I ask because if there is another problem i should be looking at that made the transistors blow.
Can't wait to get the new transistors in.
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Old 7th February 2009, 01:57 PM   #10
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You are right.
Before replacing burnt transistors, try to see if there can be any reason for those were destroyed.
If there is still such a reason, then same might happen again.
Now, this is not easy to find out, not even if you are experienced.

Usually, there is no such reason, fault. And you should be ok put in some new Transistors.
Because mostly, transistors blow for example, when somebody happpen to shorcut the output + and - terminals
or maybe accidently put some water into the amplifier, and such ....

These reasons are things that were temporary and not present now.
----

Please, make sure there are working FUSES, with original rating.
Before you power up again.
-----

About SANKEN transistors.
They are not too difficult to find, if you make a Google search.
This is one place to buy http://www.ampslab.com/trans_2sc3264.htm
But you can make a search and see for alternatives.
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