At this point, I'll take one. Better than none!
I'll contact the seller and ask for some pics.
Glenn
No pic from ebay seller so far.
Looking for suitable replacement part I found this dual FET from NEC-UPA68H, noted as a 2Sk150A replacement.
Any thoughts?
Price $0.90 of UPA68H,UPA68H series data sheet pdf,UPA68H picture,UPA68H manual
Thanks!
Looking for suitable replacement part I found this dual FET from NEC-UPA68H, noted as a 2Sk150A replacement.
Any thoughts?
Price $0.90 of UPA68H,UPA68H series data sheet pdf,UPA68H picture,UPA68H manual
Thanks!
Thanks Salas.
I did order those 2SK117's from the source in Germany you recommended, so I can use them.
Glenn
You bet!
I was disappointed that the static did not go to the right channel.
The tech will need to dig deeper.
Update...Ugggg
The tech told me the problem is in the left channel output stage. He said the output transistors and drivers need replacing. He said he couldn't get the parts and frankly it would be a pain in the *** to fix and not worth it, which I strongly disagree. This is an outstanding sounding rare amp, and expensive if you can even find one.
So, I need to look at the service manual, figure out where they are and which transistors need replacing and track them down, or suitable replacements. Once I have the parts, I'll try to convince him to fix it.
Any suggestions for parts and sources would be greatly appreciated.
Glenn
The tech told me the problem is in the left channel output stage. He said the output transistors and drivers need replacing. He said he couldn't get the parts and frankly it would be a pain in the *** to fix and not worth it, which I strongly disagree. This is an outstanding sounding rare amp, and expensive if you can even find one.
So, I need to look at the service manual, figure out where they are and which transistors need replacing and track them down, or suitable replacements. Once I have the parts, I'll try to convince him to fix it.
Any suggestions for parts and sources would be greatly appreciated.
Glenn
Hmmm... interesting.
I'll need to grab a copy of the manual again so probably tomorrow before I can look properly.
Drivers generally and also the VAS transistor (voltage amplifier stage) can be troublesome generally... I don't know why... but it is a peculiar affliction of Japanese transistors of a certain era. That is not to say that this is definitely the cause of your troubles though.
As we are into fault finding, does the problem appear from cold or only after the amp has been on a while ?
Edit... the output devices would be way down the list of suspects in my experience.
I'll need to grab a copy of the manual again so probably tomorrow before I can look properly.
Drivers generally and also the VAS transistor (voltage amplifier stage) can be troublesome generally... I don't know why... but it is a peculiar affliction of Japanese transistors of a certain era. That is not to say that this is definitely the cause of your troubles though.
As we are into fault finding, does the problem appear from cold or only after the amp has been on a while ?
Edit... the output devices would be way down the list of suspects in my experience.
OK, I'm just looking at the circuit again.
This is a hugely complex amp and as such I'm not so sure that just replacing in hope is going to be the answer.
If I had this in front of me I would first of all determine if the problem was continuous, that is its constant from a cold start all through it reaching normal temperature.
If its temperature sensitive then careful use of freezer spray dripped a drop at a time on suspect parts would be the next step.
I would also try and see if the problem was 'tapable' by using a plastic instrument to press and prod the PCB with it on.
Faults like this don't follow a pattern of being able to see at which point into the circuit the problem is because of the action of negative feedback with the amplifier being a 'loop'. Typically the noise, although measurable at the output would alos be seen at all other points in the circuit too.
You might try swapping drivers etc if push came to shove. Typically that would either reveal the issue by the fault swapping channels or more likely the fault would be 'fixed' as the heat from the iron temporarily fixes the issue.
I see a lot (an awful lot) of small value caps in the pf range. If they are ceramic or mica types then they can be prone to failure (intermittent leakage is common) and that would show as noise.
Also, don't discount going over all the joints on the PCB visually and reflowing any suspect devices. The transistors might typically will be found to have poor 'wetting' of the solder when you reflow them with the solder not taking to the lead... another common issue.
That's probably enough to be taking in at the moment
This is a hugely complex amp and as such I'm not so sure that just replacing in hope is going to be the answer.
If I had this in front of me I would first of all determine if the problem was continuous, that is its constant from a cold start all through it reaching normal temperature.
If its temperature sensitive then careful use of freezer spray dripped a drop at a time on suspect parts would be the next step.
I would also try and see if the problem was 'tapable' by using a plastic instrument to press and prod the PCB with it on.
Faults like this don't follow a pattern of being able to see at which point into the circuit the problem is because of the action of negative feedback with the amplifier being a 'loop'. Typically the noise, although measurable at the output would alos be seen at all other points in the circuit too.
You might try swapping drivers etc if push came to shove. Typically that would either reveal the issue by the fault swapping channels or more likely the fault would be 'fixed' as the heat from the iron temporarily fixes the issue.
I see a lot (an awful lot) of small value caps in the pf range. If they are ceramic or mica types then they can be prone to failure (intermittent leakage is common) and that would show as noise.
Also, don't discount going over all the joints on the PCB visually and reflowing any suspect devices. The transistors might typically will be found to have poor 'wetting' of the solder when you reflow them with the solder not taking to the lead... another common issue.
That's probably enough to be taking in at the moment
Lol, you might think twice when you see what I just posted
First steps are to try and get a handle on the issue... any specific conditions it occurs under and so on.
A hair dryer to heat areas of the circuit is another recognised tool of the trade to try and find thermally defective components.
Lol, you might think twice when you see what I just posted
First steps are to try and get a handle on the issue... any specific conditions it occurs under and so on.
A hair dryer to heat areas of the circuit is another recognised tool of the trade to try and find thermally defective components.
Hi Mooly,
The noise starts almost immediately after power is turned on. So warm up is not a factor. The tech said he disconnected everything, narrowing it down to the output stage, left channel.
Cheers, Glenn
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