Hi everyone, i opened thread about 2N6488 transistors because are broken in this amp, and the new generation of this semiconductors cause issues.
That i think.
https://www.diyaudio.com/forums/parts/335908-2n6488-2n6488.html
Otherwise, what is the likely solution?
To slow down slew rate with capacitors like suggest from indianajo?
Please you're welcome for every aid and i appreciate it.
Someone can give the scheme?
Thanks.
That i think.
https://www.diyaudio.com/forums/parts/335908-2n6488-2n6488.html
Otherwise, what is the likely solution?
To slow down slew rate with capacitors like suggest from indianajo?
Please you're welcome for every aid and i appreciate it.
Someone can give the scheme?
Thanks.
I have buied the new transistors Onsemi 2N6488 from Mouser.
But appears the new generations semiconductors with a super gain, over specs.
This is i understand from indianajo post.
That's inexplicable for me.
The power supply of this Orion model not have IC for switching's frequency, it's self controlled.
With a pair of new 2N6488 the amp start well, if i put the second couple the power supply works still, but after two minutes i turn off the external power supply and re turn on, now the switching goes into crisis and current's request to stars.
I suspect this happen with semiconductors just warm.
With one pair only, no issues.
Thanks Perry.
But appears the new generations semiconductors with a super gain, over specs.
This is i understand from indianajo post.
That's inexplicable for me.
The power supply of this Orion model not have IC for switching's frequency, it's self controlled.
With a pair of new 2N6488 the amp start well, if i put the second couple the power supply works still, but after two minutes i turn off the external power supply and re turn on, now the switching goes into crisis and current's request to stars.
I suspect this happen with semiconductors just warm.
With one pair only, no issues.
Thanks Perry.
1 Can you measure the rail voltage when it's using only 2 PS transistors and with 4?
2 To measure rail voltage, you must use the secondary ground (RCA shields).
3 How much current is 'to stars'?
4 Is there any current limiting in the B+ line?
5 Do the PS transistors fail if clamped tightly to the heatsink?
2 To measure rail voltage, you must use the secondary ground (RCA shields).
3 How much current is 'to stars'?
4 Is there any current limiting in the B+ line?
5 Do the PS transistors fail if clamped tightly to the heatsink?
1 With a pair at 13,0v have 0,60A absorption and rail voltage +/- 19,15v.
Two pair at 13,0v have 0,59A absorpion and rail voltage starting +/- 19,15v to +/- 19,30v then two transistors of part left too much warm.
With three couple the power supply don't turn on, with all cold too.
4 +B line current limiting 5A
3 When power supply goes into crisis the line +B goes until 4,55A and voltage +B alight to 8,00v
+B's limiter intervenes.
5 Tests withouth heatsink
This is a good news, thank you.
I'm trying to buy some Motorola old stock, for to fix this amp and storage some of these transistor for the future.
I send you pm.
Have you fix this amp with a normal substitution of transistors?
Nothing else?
These amplifier won't generally power up through a current limiting resistor.
I'd suggest installing all of the transistors, inserting a 10 amp fuse in the B+ line, clamping all transistors to the heatsink and seeing if it will power up (no limiter).
Did you have any of the original PS transistors that survived?
I'd suggest installing all of the transistors, inserting a 10 amp fuse in the B+ line, clamping all transistors to the heatsink and seeing if it will power up (no limiter).
Did you have any of the original PS transistors that survived?
I mounted all transistors, and wired to +B line with fuse 10A: the amp works.
I did try with 7,5A fuse, the amp works.
I did try with 5A fuse too, and the amp works!
The limiter of my power supply is 5 A, i don't understand.
I say that because another equal amp but fully original, and wired with the limited power supply it works.
The current peak at turn on is 4 A.
Can you tell me why the same amp but repaired not works with this power supply?
More gain of new transistors?
I did try with 7,5A fuse, the amp works.
I did try with 5A fuse too, and the amp works!
The limiter of my power supply is 5 A, i don't understand.
I say that because another equal amp but fully original, and wired with the limited power supply it works.
The current peak at turn on is 4 A.
Can you tell me why the same amp but repaired not works with this power supply?
More gain of new transistors?
I don't have an answer why. Maybe they changed something in the windings for the drive circuit. I just remember that these amps had me scratching my head (confused) when I was repairing them and they wouldn't power up and would draw excess current through a current limiter.
The larger 2350 has trouble starting on a 20 amp supply if the wire isn't large enough, even though the wire is good for most all other amps. The self-oscillating amps do strange things, sometimes.
The larger 2350 has trouble starting on a 20 amp supply if the wire isn't large enough, even though the wire is good for most all other amps. The self-oscillating amps do strange things, sometimes.
About strange things, the amp failed again.
Now it turn on withouth remote current.
I connect the positive and negative and it start but it play with a very bass level, and when i increase the volume the sound disappear.
With remote consent or without it, nothing change.
It's incredible, the amp did work normally.
I reassembled it with definitive weldings and it has changed.
Now it turn on withouth remote current.
I connect the positive and negative and it start but it play with a very bass level, and when i increase the volume the sound disappear.
With remote consent or without it, nothing change.
It's incredible, the amp did work normally.
I reassembled it with definitive weldings and it has changed.
The owner i'm me.
I think a control problem because i unsoldered all PS transistor's bases, and soldered one pair only, but the issue remains.
Before not did have it, and with a pair it did works.
Then i tried to put a capacitor 1 nF between base and collector each branch withouth results.
I heard a little bang only, like a fuse broken, but i haven't noted any break.
So i have removed the caps.
I think a control problem because i unsoldered all PS transistor's bases, and soldered one pair only, but the issue remains.
Before not did have it, and with a pair it did works.
Then i tried to put a capacitor 1 nF between base and collector each branch withouth results.
I heard a little bang only, like a fuse broken, but i haven't noted any break.
So i have removed the caps.
I recently repaired one of these that would power on with no remote, power on with remote and not power off, no regulation all kinds of issues. I ended up replacing all diodes, transistors, capacitors, the 2 optos, and any resistor that was out of spec. This was in the power supply as the outputs were ok. It worked great after that, until then it was just chasing my tail.
You've replace a very lot of components, i didn't imagine those could be out of specs.
Have you replaced those into power supply section only?
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I've removed that transistor, with one pair only power transistors and 10A fuse but the amp turn on withouth remote.
The power on led blink slowely, sometimes turn off but after it turn on again.
So it can blink very slowely or to stay turn on or turn off for some seconds or minutes.
With the axial cap in the power input the connection make a little spark, every contact.
If i desold the cap, not have spark.
If i remove this cap, the diode in the power input, and the two optos and withouth the 2N488 driver, the amp turn on withouth remote again.
But after these two week the power on is more slowely and not regular, like the led's light.
I connect the amp for to test with crocodiles cables, and between two of those i put the fuse.
The power supply unit is a 30A-13,8v continues
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