Sansui AU-999 dead right channel

[blacknapkins]

Sansui AU-999 dead right channel-IT'S ALIVE!

I'm a newbie here but have all of my orginal Pioneer & Kenwood equipment from the 70's. I recently picked up an AU-999 amp & was excited to try it out.
I do not have any manuals but it appears that the right channel is out. The left channel works in both A & B speaker selection. The right does not. I had the cover off before I tried it out & it is fairly clean inside. Any suggestions on what the problem could possibly be?

thanks
Blacknapkins

 

[jblmar]

First, welcome to AK.
You'll need to check voltage at the putput transistors. You can use the working channel as an indication until the manual arrives. You should find +/- xx VDC at the collector (the outside case) of the transistor. Compare to the nonworking channel.
This won't isolate the problem, but it's a start for now. Post your findings.

Ron

 

[bangsezmax]

First, check the output fuses on the back of the unit. If those are good, take the cover off and check the rail fuses inside the unit. There are two 5A fuses for each channel in housings with a clear plastic cover. If either of those are bad, replace them.

I own one (great units with a wonderful phono stage) that had a fuse blowing issue -- on mine, one channel would blow one of these rail fuses and go out. Turns out it was an overheating/failing transistor on one of the driver boards. If I opened the case and put a fan next to it, the fuse wouldn't blow. Once the transistor was replaced, it worked fine. (Wish I could tell you that I had done the circuit tracing and transistor replacement, but I'm not as electronically inclined as I'd like to be).

If you look in the case, there are two vertical driver boards with edge connectors on this unit (pretty easy to spot). You can try swapping them and see if the problem moves from the right to the left (IIRC, you will have to disconnect them from the heatsinks, but this isn't complicated). If the issue moves with the boards, you have at least isolated where your issue is.

Goood luck!

 

[blacknapkins]

Dead Right channel

Bangsezmax,

I owe you a cold one. I swapped the rear output fuses & bang.
The right channel works now & the left doesn't.

Please excuse my amateurness on this....my Kenwood & Pioneer stuff that I bought in the 70's & still have is pretty much entry level (none of these fancy fuses & I'm learning.) This unit sure sounds a lot more crisp & clear than my Pioneer receiver.

Can anyone tell me what spec fuses should be in this amp? One fuses looks like it reads 5A 32V & the other one is either 5A 250V or 25V ?

Thank you,
Blacknapkins

 

[tarior]

Bangsezmax,

One fuses looks like it reads 5A 32V & the other one is either 5A 250V or 25V ?

Thank you,
Blacknapkins

Throw that 5A 32V in the trash and replace it with a 5A 250V.

 

[bangsezmax]

I swapped the rear output fuses & bang.
The right channel works now & the left doesn't.

Ok -- Hopefully the fuse will put you back in business. If it still blows fuses after you have the right ones, you can try swapping those boards I mentioned above and see if the problem moves with it.

Just as a question, did you look at the bottom of the unit to see if the schematics were there? Lots of (all?) Sansuis from that era came with the schematics in an envelope stuck to the bottom of the unit.

Please excuse my amateurness on this....my Kenwood & Pioneer stuff that I bought in the 70's & still have is pretty much entry level (none of these fancy fuses & I'm learning.) This unit sure sounds a lot more crisp & clear than my Pioneer receiver.

I'm an amateur too, just one who's been around the block with this particular amp. I bought mine at a thrift store here in Durham about 17 years ago. Twenty bucks well spent. It was my main rig for many years. Now it runs the rear speakers (Infinity SM-100s) in my "vintage" surround setup.

It was the top of Sansui's consumer line at the time. An interesting amp sonically. Clean and uncolored, but not as crispy bright as other "signature" Sanuis I've owned (a G9000DB and a 9090DB). Think a tube-like tonal spectrum without the saturation that you get with real tube outputs. That's what the AU-999 sounds like to me.

 

[markallen]

6v DC on One Channel

Going to pick up this old thread, as I've got a channel problem on my AU-999 too. While one channel reads 25 mV at the speaker outputs, the other reads 6 volts (volume turned down w/ no input). Not huge, but certainly not good.

As the small amp boards match, I swapped the L & R channels boards (love these plug in PCBs!) - and the output figures switched with the boards, indicating to my satisfaction that the problem is on the (now L) F-1159 board! I figure one of the resident AK Sansui experts will recognize this problem, and likely even know which component(s) is/are the culprit(s). I'm thinking transistor, as other threads indicate these "flying saucer" style transistors all need to be replaced - but will that solve this problem? I've attached a photo in case that will help.

 

[markallen]

A quick check of the transistors on that board doesn't reveal any of them are bad, but being in-circuit may affect the results.

 

[Drew13]

Wow this 10 year old post saved me a lot of time and effort. I had the exact same thing just happen on my au-999, but it was the left side that died. I had completely forgot about the output fuses and only checked the internal ones. Wouldn't you know the fuse was busted. Thanks bangsezmax.

 

[LBPete]

Hi Drew, welcome to AudioKarma Exclusively Sansui Forum. As you have seen, there is a lot of good information here. Can you post the serial number of your AU-999 for the database? Just click on the link in my signature block.

- Pete

 

[bangsezmax]

Glad it helped! My AU-999 is long since sold. She's making music for somebody else now.

 

[Drew13]

Well it turns out my problem is a little bit more than a busted fuse as the right channel seems to have died again. I will post the serial number of my 999 when I get a chance. Time to break out the multi meter...

 

[kevzep]

There is usually something which causes the fuse to blow, sometimes its just a random event but often its a sign there is something else wrong.
Does it have original transistors through it?
The ones that look like Flying Saucers?
If it does, you are needing to get rid of them, might as well recap at the same time, and do the mods all at the same time.

So pop all the boards out and start making a cap list.
There's tons of information here in this forum to help you find the right subs....

 

[Drew13]

Yep, she is all original with the exception of 1 flying saucer transistor my dad replaced in the 80s. I have been looking into the 999 mods and they seem simple enough. I know a place where I can buy all of the parts but probably wont be able to work on it till I am out of school. Till then my 2000X will have to hold me over.

 

[kevzep]

Yep, she is all original with the exception of 1 flying saucer transistor my dad replaced in the 80s. I have been looking into the 999 mods and they seem simple enough. I know a place where I can buy all of the parts but probably wont be able to work on it till I am out of school. Till then my 2000X will have to hold me over.

They are pretty easy amps to work on, and there is lots of info on this site, plus you have a bunch of guys here who can help if you get stuck.

 

[Yellowyoda]

6v DC on One Channel

Going to pick up this old thread, as I've got a channel problem on my AU-999 too. While one channel reads 25 mV at the speaker outputs, the other reads 6 volts (volume turned down w/ no input). Not huge, but certainly not good.

As the small amp boards match, I swapped the L & R channels boards (love these plug in PCBs!) - and the output figures switched with the boards, indicating to my satisfaction that the problem is on the (now L) F-1159 board! I figure one of the resident AK Sansui experts will recognize this problem, and likely even know which component(s) is/are the culprit(s). I'm thinking transistor, as other threads indicate these "flying saucer" style transistors all need to be replaced - but will that solve this problem? I've attached a photo in case that will help.

Sorry, I know this thread goes back a bit but i do seem to have the same symptoms as you have. I acquired a very clean Au999 which had no sound from the left channel I noticed there was a blown internal fuse (F3) replaced this and had sound from both again for about a day then heard some distortion and intermittent sound from the
left channel and then no sound from the left channel. I replaced F3 again but no sound from the left channel. I then checked the exterior fuses and F1 had blown.
It seems that this seems to be a driver transistor problem (probably) - did you find out which transistor is the culprit? There are a few that it could be TR801,803,805,807,809,811or 813? It could be 1 or more i guess but if you could offer any pointers I'd be obliged. Thanks.

 

[slimecity]

I noticed there was a blown internal fuse (F3)

Find and download the service manual at hifiengine.com

I cant recall but fuse F3 may be for setting bias.

I've had mine blow a couple of times and the bias just needed readjusting.

If fuse F3 is for bias - then check how much bias you are getting by measuring across the emitter resistors in mV (easier than the SM method of measuring in mA across the empty fuse holder).

 

[kevzep]

F3is not for bias, it is the main +44V rails for the Positive drivers and Positive output transistors. B1 for Left channel, and B2 for Right.
If F3 is blowing there is too much current being drawn by the output section and could indicate a blown output or driver.
You would need to have bias wound up over 20 times the rated setting to actually pop a fuse, at which point you'd probably blow a device...

So long story short, you need to look at these transistors.

If you are now blowing a mains fuse, you may have stressed and blown the bridge rectifier.

So do not put any more fuses in and do not power it up until we find out what the issue is.

 

[Hyperion]

Also it is not recommended to perform any blanket replacement of components until the issue is resolved. Just find and change the faulty parts first, get it going, and only then consider further parts replacement to freshen the unit up.

 

[Yellowyoda]

F3is not for bias, it is the main +44V rails for the Positive drivers and Positive output transistors. B1 for Left channel, and B2 for Right.
If F3 is blowing there is too much current being drawn by the output section and could indicate a blown output or driver.
You would need to have bias wound up over 20 times the rated setting to actually pop a fuse, at which point you'd probably blow a device...

So long story short, you need to look at these transistors.

If you are now blowing a mains fuse, you may have stressed and blown the bridge rectifier.

So do not put any more fuses in and do not power it up until we find out what the issue is.

Thanks Kevzep, Slimecity and Hyperion. That's a great help. I had a suspicion that the problem may be a bit more of an issue when the previously Intact Fuse F1 blew.
I was hoping that it might be something I could fix and when I replaced F3 initially it did sound fine (for the rest of the day). I think this may be a job for a tech, I certainly don't want to risk making the situation worse. It is remarkably clean inside -almost like new infact.
Thanks again gents.