Sansui AU-X1 and the UPA68H

slimecity

Super Member
Hi all -

Kevzep and I have gone thru my X1 and I have a nagging issue in the flat amp board. Kev replaced pretty much all the transistors in there, and I replaced all the zeners. That only left the caps - which I fully re-did tonite.

The only original semiconductors in there are the two UPA68H. Tonite I was testing it and I was sure I heard the dreaded "crack bang pop" again - this is what I have been chasing. Its always in the right channel and goes away totally when pressing the jump switch (bypassing the flat amp). Its worse in the cold - ie: with cold starts.

Questions:

There are mixed views on using freeze spray on fets - can I do it safely on these fets - given that I am not going into the poweramp section (I am running a feed out of the preamp out RCA's to my 555a). The amp is switched to seperate when I do this.

I have some spare UPA68H - two pairs. The first pictured ones came from UTSource (same size as the fitted ones), the second from LittleDiode (I think, these are smaller, a slightly different type - it was a supposedly more reputable supplier but I got these a while ago).

Do any of these look genuine? I dont have a curve tracer. Does anyone have a source for these they completely recommend getting good parts from?

Cheers!

Screen Shot 2018-09-20 at 7.47.50 PM.png IMG_4787.jpg IMG_4786.jpg
 
I assume this happens in one channel only? - if that is the case what about swapping 2 UPA68H around, from one channel to the other?
 
I assume this happens in one channel only? - if that is the case what about swapping 2 UPA68H around, from one channel to the other?
Yes - that sounds like an idea.

Would like to try freeze spray first if its an option - if not - then yes - I guess swapping would be the the way positively identify the suspect part.

But the issue is that the fault is very intermittent and I think putting the parts into a cold state is more likely to trigger the fault state.
 
hit it with the freeze spray, I use it on these sort of components frequently...

a little dab will do ya....

Dont worry about putting it into that state this is what you want to do to confirm what we suspect, and dont worry about damaging it, if its shot then its shot.....freeze spray wont change that, and it wont damage one which is not faulty...
 
Ok fair enough, with the freeze spray you shouldn't have to blast it until there is frost on the UPA case, just a very brief squirt should be enough. Also I have in the past spent some time making a little cardboard shield to put around a suspect component, in order to shield nearby components from the freeze spray blast, and thus be much more confident (in the case of a positive reaction) that the suspect component is the culprit. ;) maybe that won't be necessary here.

Kev and my posts simultaneous :)
 
Hmmm, it was a mission getting to the parts with having the preamp section running - but managed to squirt the FETs with spray on both sides - a few times.

I think you are right about these being pretty rugged Kev - no issues on either side. I also cleaned the hell out of the DC offset trimpots on that board and these appear to be running smoothly and holding their values when adjusting.

Chances are that my issues are being caused by the small signal relays in the phono master board. I will recap the regulated powersupply section then the next step is populating & dropping in Ron's new Phono motherboard. I think I need to do that first to rule out these relays as being the culprit.

Cheers all for input
 
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Hello Slimcity , hello Kevin

I have ordered some µPA68H from UT source and I received after some days µPA68H looking like original but empty !! if I try to make measurement on each pin , I have nothing !! I send them (6 pieces) back to UTSource and ask for refund . Since over a year I never received any news and most important no refund , never !
I will strongly recommend you to think twice before to buy anything from them . From my part I stop all my bought and they don't care .
Kevin , I will try if I can get some from another place (reliable this time) and let you know
Do not use yours IC without to check them but I will not be surprised that you will find nothing in the package (no component say my PEAK )

Fake-µPA68H.jpg


Fake-ICs.jpg
 
if I try to make measurement on each pin , I have nothing !!
Thanks for this - I wont use those parts.

I have to say that I havent tried to test them yet. If you find a reliable source for genuine parts, please do let me know.

I found the issue with my noise - it was actually a pass-thru from the reg power supply going to the flat amp that needed reflowing - so I reflowed the entire flat amp board and now no issues!

Currently doing the recap on the reg power supply board - halfway thru - and will also reflow all joints on that once recapped
 
Original ones are long gone. You can make them out of a matched pair of 2SK117's. I have done this, but beware of fakes of these as well.
 
Hello Slimcity , hello Kevin

I have ordered some µPA68H from UT source and I received after some days µPA68H looking like original but empty !! if I try to make measurement on each pin , I have nothing !! I send them (6 pieces) back to UTSource and ask for refund . Since over a year I never received any news and most important no refund , never !
I will strongly recommend you to think twice before to buy anything from them . From my part I stop all my bought and they don't care .
Kevin , I will try if I can get some from another place (reliable this time) and let you know
Do not use yours IC without to check them but I will not be surprised that you will find nothing in the package (no component say my PEAK )

View attachment 1291397


View attachment 1291398
I have never bought from that company, I have never bought these FET's before.....I am very cautious about this sort of thing........
 
They will work great. You have to get creative installing them where the SIP was, but I think you can figure it out. They must be thermally coupled. Glad you found the issue!
 
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