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.
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.
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.
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.
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.
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
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
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/search.php?q=2sc3264&searchtype=default&p=1
They are very good and big power transistors 😎
to see what is the
B - base
C - collector
E - emitter
of the Sanken 2SC3264 and other
http://www.datasheetarchive.com/search.php?q=2sc3264&searchtype=default&p=1
They are very good and big power transistors 😎
Attachments
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?
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?
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.
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.
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.
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.
lineup,
thank you for all your help.
I hae placed an order for all the transistors and as soon as they arrie i will put them in and let you know the outcome.
I think that if the transistors blow again, then i will sell the unit on to someone with a lot more experience in electronics than i.
I will ensure that there are 4 new fuses as described in service book, just as a precaution, because they all test good.
thank you for all your help.
I hae placed an order for all the transistors and as soon as they arrie i will put them in and let you know the outcome.
I think that if the transistors blow again, then i will sell the unit on to someone with a lot more experience in electronics than i.
I will ensure that there are 4 new fuses as described in service book, just as a precaution, because they all test good.
Ok, the transistors came and i have replaced all the blown transistors. When i switch on, still nothing
Absoloutly nothing happens, as if there is no plug inserted in the mains. I have checked the mains cable and it is fine.
Please help! What can be the problem now?
Absoloutly nothing happens, as if there is no plug inserted in the mains. I have checked the mains cable and it is fine.Please help! What can be the problem now?
Did you check the drivers and predrivers too, these usually go along with the output. Because the cascode on the vas is connected to the output these are probably gone too heaven too and taken the vas ones with it. Also check q755, q753 and q617.
This amp sounds pretty good and is powerfull enough to shake the room and wake the neighbours a mile away, worth fixing even if you have to replace all those transistors.
Forgot one thing, check if the emitter resistors are ok and some didnt go open circuit.
This amp sounds pretty good and is powerfull enough to shake the room and wake the neighbours a mile away, worth fixing even if you have to replace all those transistors.
Forgot one thing, check if the emitter resistors are ok and some didnt go open circuit.
Will take the pcb's out again and start de-soldering and checking other components.
Could it be the transformer(s)? There are two massive ones (as big as a new born baby head).
Thanks!
Could it be the transformer(s)? There are two massive ones (as big as a new born baby head).
Thanks!
I dont think theres anything wrong with the transformers, this amp has protection relay which is most probably kicking in because theres still a fault somewhere, but you could check the voltages across the secondries to be sure. I think the previous owner just shorted the outputs with the consequint results.
Have taken the pcb that had the blown transistors on it and have de-soldered and checked the four other small transistors (bolted to 4 small heatsinks on the pcb) and these test fine.
Also i have de-soldered and checked 2 even smaller transistors (no heat sink) and they test fine.
Also, i have de-soldered and tested 2 quite large resistors that are situated near the 2 fuses and these test fine.
I am begining to think it maybe something in a different area and not on this pcb, any thoughts?
Thanks.
Also i have de-soldered and checked 2 even smaller transistors (no heat sink) and they test fine.
Also, i have de-soldered and tested 2 quite large resistors that are situated near the 2 fuses and these test fine.
I am begining to think it maybe something in a different area and not on this pcb, any thoughts?
Thanks.
Hmmm... You may want to take out those 10A fuses supplying both amplifiers and start checking some voltages from the mains through the filtering caps. Furthermore, there is a small transformer supplying soft-start circuit, with two fuses around it. Check them out. If your soft-start relay does not work, then everything else is dead too.
Also, you have two more fuses (T2A) supplying two AD711 operational amplifiers, as well as output protection relays. Once you check out if all of this is OK and voltage ready, you may want to examine things further.
Hope this helps...
Also, you have two more fuses (T2A) supplying two AD711 operational amplifiers, as well as output protection relays. Once you check out if all of this is OK and voltage ready, you may want to examine things further.
Hope this helps...
I have had this amplifier to bits and there seems to be some difference in the schematics i found through 'hifiengine', like the fact that there are only 4 fuses, 2 on each pcb which are now all new.
I have just re-checked the pcb and i had forgotten about a transistor (2sd1953 - one per pcb)that is bolted to the front of one of the big output transistors and is not soldered but is in a clip that has wires going to the pcb. I unbolted and unclipped it and then tested it, although not shorted liked the previously replaced transistors - it seems to measure unlike any transistors i have tested in this amp. I have ordered 2 of these and will see what happens.
I have just re-checked the pcb and i had forgotten about a transistor (2sd1953 - one per pcb)that is bolted to the front of one of the big output transistors and is not soldered but is in a clip that has wires going to the pcb. I unbolted and unclipped it and then tested it, although not shorted liked the previously replaced transistors - it seems to measure unlike any transistors i have tested in this amp. I have ordered 2 of these and will see what happens.
2SD1953 is a Darlington transistor with built in resistors (2 of them) and diode connecting collector end emitor, so it's quite OK that it doesn't measure as the rest of the (normal) bunch. See it's datasheet for details - datasheet
I'm puzzled by the big differences between service manual and the real thing. Normally, differences are just in details.
I'm puzzled by the big differences between service manual and the real thing. Normally, differences are just in details.
q755 q753
yes, i am puzzled also. It's not just the fuses that are different, 'homemodder suggested i look at Q755 and Q753, both of which are in the service manual but not on the pcb's found in my amp. Q617 is present and is the darlington 2sd1953 which is not just testing different values but also differently from any transistor i have tested. Measurement from collector to emitter measures correctly one way but when probes are reversed the measurement is different (not 'ol' but 1.9). Would this be a faulty transisitor?
yes, i am puzzled also. It's not just the fuses that are different, 'homemodder suggested i look at Q755 and Q753, both of which are in the service manual but not on the pcb's found in my amp. Q617 is present and is the darlington 2sd1953 which is not just testing different values but also differently from any transistor i have tested. Measurement from collector to emitter measures correctly one way but when probes are reversed the measurement is different (not 'ol' but 1.9). Would this be a faulty transisitor?
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