D
Deleted member 543346
I need new output transistors , as the old ones are shorted in one channel.
Original transistors:
2sc3856
2sa1492
What replacements could i use?
So far i have looked at :
NJW 0281g / 0302g
NJW 1302g / 3281g
2sc 5200n / 2sa 1943n
2sc 5242 / 2sa 1962
I am limited by space for mounting transistors , so replacement cannot be larger than the originals.
Will change all output transistors
Original transistors:
2sc3856
2sa1492
What replacements could i use?
So far i have looked at :
NJW 0281g / 0302g
NJW 1302g / 3281g
2sc 5200n / 2sa 1943n
2sc 5242 / 2sa 1962
I am limited by space for mounting transistors , so replacement cannot be larger than the originals.
Will change all output transistors
Hi RagnarB,
I was authorized warranty for those amplifiers and still work on them. Let me just say I am very impressed you have a blown output stage. I only ever saw one, and that was due to a heavy copper box staple that fell inside. The staple did not survive.
I have used the NJW0281/0302 in other repairs and love them. The NJW1302/3281 would also work fine. These appear to be obsolete numbers though. I found beta match on the NJW0281/0302 to be excellent. These are more than good enough.
I was authorized warranty for those amplifiers and still work on them. Let me just say I am very impressed you have a blown output stage. I only ever saw one, and that was due to a heavy copper box staple that fell inside. The staple did not survive.
I have used the NJW0281/0302 in other repairs and love them. The NJW1302/3281 would also work fine. These appear to be obsolete numbers though. I found beta match on the NJW0281/0302 to be excellent. These are more than good enough.
D
Deleted member 543346
Hi Anatech.
I really appreciate your insight , and will not order the NJW 0281 / 0302.
Amplifier was a mess when i got it , and to be honest i have problems understanding how it should be.
The alignment of the amplifier seem to differ a bit regarding trimpots.
Besides the bias trimpot there is another trimpot that affects the vas i think...yes here the water gets deep for me😅.
This second trimpot does not show in servicemanual.
Amplifier was alive after changing a few of the blown outputs (2 times) , drivers , resistors and diodes in left channel
Now i am out of original transistors.
Had it running on dimbulb just for test , and it seemed to draw alot current from left channel.
I really appreciate your insight , and will not order the NJW 0281 / 0302.
Amplifier was a mess when i got it , and to be honest i have problems understanding how it should be.
The alignment of the amplifier seem to differ a bit regarding trimpots.
Besides the bias trimpot there is another trimpot that affects the vas i think...yes here the water gets deep for me😅.
This second trimpot does not show in servicemanual.
Amplifier was alive after changing a few of the blown outputs (2 times) , drivers , resistors and diodes in left channel
Now i am out of original transistors.
Had it running on dimbulb just for test , and it seemed to draw alot current from left channel.
You have an earlier model maybe with the second trim pot. That affects driver bias a lot as I recall. If the controls have been disturbed I'll have to check my notes to see what is normal. It would take some digging, and I have had to adjust one before as another tech was loose inside.
Others may differ on my opinion, but if you have one shorted output, you have to change them all and the drivers. If one shorts, it was just the first to fail, the others were stressed close to failure. Then the other polarity bank had to conduct far more than their design maximum. Likewise the drivers were operated outside of their design. This is true of all amplifiers. I serviced that one blown amplifier this way with the blessing of Nakamichi.
It is no surprise if you think about it, the dim bulb tester is a bad idea. Use a variac please. If you have high current draw on one channel, trace the fault at reduced supply voltage. The dim bulb will increase supply voltage as the current drops without you knowing. Don't play games on the bench.
Check for bad solder connections on Q110, Q111, Q112. Also on the bias PCB, and if it has been pushed down it may intermittently short. Look out for other things the previous person did. We called it "panicking technician syndrome" where they do things that don't make logical sense.
Others may differ on my opinion, but if you have one shorted output, you have to change them all and the drivers. If one shorts, it was just the first to fail, the others were stressed close to failure. Then the other polarity bank had to conduct far more than their design maximum. Likewise the drivers were operated outside of their design. This is true of all amplifiers. I serviced that one blown amplifier this way with the blessing of Nakamichi.
It is no surprise if you think about it, the dim bulb tester is a bad idea. Use a variac please. If you have high current draw on one channel, trace the fault at reduced supply voltage. The dim bulb will increase supply voltage as the current drops without you knowing. Don't play games on the bench.
Check for bad solder connections on Q110, Q111, Q112. Also on the bias PCB, and if it has been pushed down it may intermittently short. Look out for other things the previous person did. We called it "panicking technician syndrome" where they do things that don't make logical sense.
D
Deleted member 543346
Well i allways use dimbulb after repairs , and this time it was quite bright.
Its easy to say i should use variac after i notice the bright bulb , and yes i do use variac when i search for faults.
But sometimes mistakes are made..
No this model had two trimpots (confirmed by looking at pictures from same model).
Allready checked soldering , but now i am not sure the prints for transistor orientation is correct on pcb.
Orientation on left and right print differ , but on schematics they look identical.
I would think the channels was mirrored pcb's?
When increase bias on one channel , the other channel reacts by going down.
Ordered the new outputs.
Its easy to say i should use variac after i notice the bright bulb , and yes i do use variac when i search for faults.
But sometimes mistakes are made..
No this model had two trimpots (confirmed by looking at pictures from same model).
Allready checked soldering , but now i am not sure the prints for transistor orientation is correct on pcb.
Orientation on left and right print differ , but on schematics they look identical.
I would think the channels was mirrored pcb's?
When increase bias on one channel , the other channel reacts by going down.
Ordered the new outputs.
I have plenty of Sanken 2SA1294 and sibling.
R
R
Hi RagnarB,
If you are using an AC supply that varies with the load (dim bulb), your observations make perfect sense considering the bias current seesaw effect. Variac please.
The PCBs are not the same. You could call them mirrored. I have pictures of PCBs if that will help you. PM me.
Yes, I have worked on units with two trim pots. The manual differs in that area. That trimmer has a large effect, I'll try to find my notes.
-Chris
If you are using an AC supply that varies with the load (dim bulb), your observations make perfect sense considering the bias current seesaw effect. Variac please.
The PCBs are not the same. You could call them mirrored. I have pictures of PCBs if that will help you. PM me.
Yes, I have worked on units with two trim pots. The manual differs in that area. That trimmer has a large effect, I'll try to find my notes.
-Chris
Hi Chris,
I do not believe this to be true unless it’s because you are not using the “g” suffix in the part number. They might be on backorder however.
Rick
Normally these devices are readily available. But given the factory lead-time if stockists run out you might have to wait a while.
Hi Rick,
Good news. I just searched for the base number on Digikey, didn't check Mouser. I'm glad they are still current as they are excellent devices.
Thanks Mark.
Good news. I just searched for the base number on Digikey, didn't check Mouser. I'm glad they are still current as they are excellent devices.
Thanks Mark.
I’ve been using the toshiba 2sa1943n and 2sc5200n, pretty much the same part, toshiba is more economical and have shorter lead times.
Strange, Toshiba changed 2SA1943/2SC5200 into TTA1943/ TTC5200 long time ago. Are those old stocks ? I see Mouser still selling them and more are on order.
The “N” version of the case is smaller and cheaper (true for Toshiba or ON). I’m pretty sure it’s the same innards. TTA/C come from the China factory, 2SA/C from Japan. Both still Toshiba owned. 2S versions are more expensive at the quantities we usually use. They may stick you with a tariff if you buy enough of the TT version, which may equalize the prices.
ON 0281/0302 is the same size die as the Toshiba parts. Their 3281/1302 are bigger. Even bigger than original Toshiba version from the 80’s. If I were replacing MT200’s I’d use those.
ON 0281/0302 is the same size die as the Toshiba parts. Their 3281/1302 are bigger. Even bigger than original Toshiba version from the 80’s. If I were replacing MT200’s I’d use those.
wg_ski,
I'm still confused.
Edit: Wait, you're right but you didn't specify that TTA1943/TTC5200 manufactured in China comes only in a TO-3P(N) case. What I thought all the time that 2SA1943/2SC5200 are obsolete and Toshiba transferred the manufacturing to other factory such as Unisonic, Taiwan.
I'm still confused.
Edit: Wait, you're right but you didn't specify that TTA1943/TTC5200 manufactured in China comes only in a TO-3P(N) case. What I thought all the time that 2SA1943/2SC5200 are obsolete and Toshiba transferred the manufacturing to other factory such as Unisonic, Taiwan.
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Yeah, I might have been confused which one was made in the China fab and which in Japan. The 2S version costs more. And it is origin (and packaging) that differentiates them. Toshiba continues to offer both. They may BE outsourcing the packaging operation (lots of them do, even some of the ON stuff).
Lots of folks are making 2SA1943/C5200 copies these days. The only copies I’ve used are the Fairchild ones. They work as expected, even though they are a different process. Toshiba uses a triple diffused process, the Fairchild are epitaxial planar (like Sanken’s good ones).
Lots of folks are making 2SA1943/C5200 copies these days. The only copies I’ve used are the Fairchild ones. They work as expected, even though they are a different process. Toshiba uses a triple diffused process, the Fairchild are epitaxial planar (like Sanken’s good ones).
D
Deleted member 543346
Installed new outputs but still have issues with bias.
There is bias on both channels , but when adjusting one channel bias up , the other channel bias drops down.
I just dont understand why it is so
There is bias on both channels , but when adjusting one channel bias up , the other channel bias drops down.
I just dont understand why it is so