Sansui eight trouble

[dr*audio]

The basic trick to this type of troubleshooting for a noise source, is to start at the input of the circuit and work towards the output. You can't short the DC path or you will turn the transistor off, or blow something up, so you short points that are AC coupled by a cap, or you use a 10uF cap to short to ground instead of a wire. When you find a place that shorting it out kills the noise, the source of the noise is on the input side of the short.

 

[blhagstrom]

The basic trick to this type of troubleshooting for a noise source, is to start at the input of the circuit and work towards the output. You can't short the DC path or you will turn the transistor off, or blow something up, so you short points that are AC coupled by a cap, or you use a 10uF cap to short to ground instead of a wire. When you find a place that shorting it out kills the noise, the source of the noise is on the input side of the short.

Thank you!

Congrats to you and many thanks to Doc for his remote troubleshooting!

Yes, and you DCinDC and Tichu. If it wasn't for you guys keeping the thread alive and asking questions, she's still be a Hanger Queen.

This is one of my favorite receivers and I'm glad to help get another one working. In my experience, ANY electrolytic cap can go bad. Also tantalums.

I've read good things about it. So far, I've had nothing but trouble with Sansui. I am looking forward to using it.

I guess anything can go bad and I've seen enough wierd things that I should know not to take anything from granted.

Many thanks again.

 

[blhagstrom]

I at least owe you guys a photo or two.

Well, I found the screws, knobs, covers, etc....

Dialed in the main amps. Still a little tricky, but finally got some "balance" and "stability".

Hauled her off the bench and hooked up some better speakers, Advent Heritage, and a recent estate find TT, Pioneer PL-400 with an Ortofon FF15E MKII.

Dug up a copy of Alan Parson's "I Robot" and fired it all up.

New caps everywhere, new transistors in the pre-amp, good replacement for the problem aluminum caps and its shear bliss.

It's been a while since I heard LP this good. Damn, maybe there is something to all the "restoration" talk.

 

[DCinDC]

yeah!

 

[dr*audio]

Suh-weet!:thmbsp:

 

[stereofun]

Kudos for sticking it out - and kudos to DCinDC and Dr.audio for giving everyone else a 101 in diagnostics - I've learned a lot from this thread!!

The Eight is a beast! - having a recapped and retranny'ed (output/driver) myself I am glad you get to enjoy the punch, dynamic, detail and separation that it is capable of. The Eight is a true gem :tresbon:

 

[blhagstrom]

Kudos for sticking it out - and kudos to DCinDC and Dr.audio for giving everyone else a 101 in diagnostics - I've learned a lot from this thread!!

As did I. And let's not leave Tichu out, he prodded me along too. Sometimes, everyone needs little help from his friends.

The Eight is a beast! - having a recapped and retranny'ed (output/driver) myself I am glad you get to enjoy the punch, dynamic, detail and separation that it is capable of. The Eight is a true gem :tresbon:

She's a keeper.

 

[Tichu]

Thank you Blhagstrom.

As I was told: "You need to go wrong to learn".

And I can assure you I learn everyday... :yes:

 

[madtech]

Yep, good call, Tichu, since troubleshooting is a little out of reach of the OP...

There are 10 each 2sc693 npn transistors on the preamp/tone board.

If the high filter reduces the noise, and you are not using the phono input for testing, then it is likely one of those.

Order ksc1845 replacements from Mouser.com and replace those transistors. They are very inexpensive. I order them a hundred at a time.

You can use these to replace the 6 phono preamp transistors (2sc632) also. It should make an improvement there as well, with reduced hiss.

The gurus here: Markthe Fixer, Echowars, etc turned me on to these.

The both channels thing is troubling, but these transistors could've gone noisy, although they are not one that's known to be. But time marches on...

Are all 10 transistors in the preamp exactly the same? I notice on the schematic some end with F, FU, E and EU. I have a Sansui Eight on the bench right now with one channel out. The power amp section is perfect so I'm leaning towards the preamp. Thanks !

Well done Blhagstrom !

 

[blhagstrom]

Are all 10 transistors in the preamp exactly the same? I notice on the schematic some end with F, FU, E and EU. I have a Sansui Eight on the bench right now with one channel out. The power amp section is perfect so I'm leaning towards the preamp. Thanks !

Well done Blhagstrom !

Yes, all KSC1845 now. These http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/KSC1845FTA/?qs=UMEuL5FsraBJNVsPff1u9hfeiwqgjAmx5mVN6lVrzhY%3d

I am operating under the assumption that the F, FU, E, EU, or whatever the trailing code is on a transitor was a "quality" rating back in the day. Some passed testing better than others. They worked a bit better. I think that also works today on new parts for tolorance ratings on caps and resistors and such (ie +/- 10%, +/- 5%, etc...)

I could be wrong, someone who really knows should chime in.

 

[madtech]

Yes, all KSC1845 now. These http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/KSC1845FTA/?qs=UMEuL5FsraBJNVsPff1u9hfeiwqgjAmx5mVN6lVrzhY%3d

I am operating under the assumption that the F, FU, E, EU, or whatever the trailing code is on a transitor was a "quality" rating back in the day. Some passed testing better than others. They worked a bit better. I think that also works today on new parts for tolorance ratings on caps and resistors and such (ie +/- 10%, +/- 5%, etc...)

I could be wrong, someone who really knows should chime in.

Thanks for that. I'll order some up tonight. Great thread, I learned a lot!

 

[blhagstrom]

What have you done so far?
You said the mains wre good, I assume you tested the boards or just swapped them (they just plug in).

You can check the pre-amp by swapping the wires at 7AL and 7AR.
If the dead side changes, its before the pre-amp.
If not, then its the pre-amp.

You could then swap all of 7K, 7L, 7M and 7N to see if its in the filter board.
Or at least before that point or after.
That filter board is a pain in the @$$ to get in and out.
There really isn't anything much on the filter board except the switches and some resistors. The other parts are part of the balance thingy.

 

[madtech]

What have you done so far?
You said the mains wre good, I assume you tested the boards or just swapped them (they just plug in).

You can check the pre-amp by swapping the wires at 7AL and 7AR.
If the dead side changes, its before the pre-amp.
If not, then its the pre-amp.

You could then swap all of 7K, 7L, 7M and 7N to see if its in the filter board.
Or at least before that point or after.
That filter board is a pain in the @$$ to get in and out.
There really isn't anything much on the filter board except the switches and some resistors. The other parts are part of the balance thingy.

Actually, so far not a lot. I've pulled the jumpers from the preamp to the mains and hooked up my Luxman preamp. The dead left channel came back to life so I know it's somewhere from the preamp back. Then I pulled the tone control board (F-1235) to check for cold solder joints and any visible problems. I'll put the board back in tomorrow night and swap 7AL with 7AR and report back. Thanks!

 

[blhagstrom]

Actually, so far not a lot. I've pulled the jumpers from the preamp to the mains and hooked up my Luxman preamp. The dead left channel came back to life so I know it's somewhere from the preamp back. Then I pulled the tone control board (F-1235) to check for cold solder joints and any visible problems. I'll put the board back in tomorrow night and swap 7AL with 7AR and report back. Thanks!

Did you clean the switches and controls well?

You do know that the pre-amp/main switch is on the speaker selector...right?
Way to the right where it has A+C and A there is marking saying pre main separated. So, no jumper needed.

Hmmm, from what info I've seen, there is a "later" model with speaker protection, so maybe there are two types? Mine doesn't need jumpers.

But I'm wondering if you may have a pre-amp/main switch and its dirty....no channel.

Not to derail a recap and re-transistor job. Mine sounds GREAT!

 

[madtech]

Did you clean the switches and controls well?

You do know that the pre-amp/main switch is on the speaker selector...right?
Way to the right where it has A+C and A there is marking saying pre main separated. So, no jumper needed.

Hmmm, from what info I've seen, there is a "later" model with speaker protection, so maybe there are two types? Mine doesn't need jumpers.

But I'm wondering if you may have a pre-amp/main switch and its dirty....no channel.

Not to derail a recap and re-transistor job. Mine sounds GREAT!

Started with a complete deoxit of all controls on the front face which was kind of a pain. I put the preamp board back in and swapped 7AR with 7AL and the other channel came up so my problem is before the preamp. I noticed a volume difference here too at this point so I will swap out all the transistors on the preamp board regardless of what else I find. The search continues....

 

[madtech]

Did you clean the switches and controls well?

You do know that the pre-amp/main switch is on the speaker selector...right?
Way to the right where it has A+C and A there is marking saying pre main separated. So, no jumper needed.

Hmmm, from what info I've seen, there is a "later" model with speaker protection, so maybe there are two types? Mine doesn't need jumpers.

But I'm wondering if you may have a pre-amp/main switch and its dirty....no channel.

Not to derail a recap and re-transistor job. Mine sounds GREAT!

Blhagstrom, sorry about hijacking your thread and thanks for the help. Before I started taking difficult to get at boards out of my Eight I thought I'd check the basics again. Grabbed my can of deoxit and hit the volume and balance knobs for the third time. At this point I noticed the volume knob was a little "sandy" compared to the balance pot. Pulled it out and looked inside it with my flashlight and there it was. The left pot slider was broken and sliding around inside the pot. Totally explains no left channel. Now I have to find a volume pot. Thanks again!

 

[blhagstrom]

ooooo

Blhagstrom, sorry about hijacking your thread and thanks for the help. Before I started taking difficult to get at boards out of my Eight I thought I'd check the basics again. Grabbed my can of deoxit and hit the volume and balance knobs for the third time. At this point I noticed the volume knob was a little "sandy" compared to the balance pot. Pulled it out and looked inside it with my flashlight and there it was. The left pot slider was broken and sliding around inside the pot. Totally explains no left channel. Now I have to find a volume pot. Thanks again!

AH HA! Now you're in trouble. I'm pretty sure that is a dual gang center tap pot. All the ones I saw, when they showed up on ebay (can't find them anywhere else) were $pendy! Although I was looking for one for a lowly 5050, the eight is probably worth the money.

I suppose a regular dual gang pot will do, but you won't be able to hook up the "loudness" wire. Sooo, if you never use "loudness" you'll be OK.

I got my eight fixed, and its a good thread for working on the eight, so keeping it alive with your troubles is fine by me. I'd love to have threads that have all the good info in them that this one does.

 

[madtech]

AH HA! Now you're in trouble. I'm pretty sure that is a dual gang center tap pot. All the ones I saw, when they showed up on ebay (can't find them anywhere else) were $pendy! Although I was looking for one for a lowly 5050, the eight is probably worth the money.

I suppose a regular dual gang pot will do, but you won't be able to hook up the "loudness" wire. Sooo, if you never use "loudness" you'll be OK.

I got my eight fixed, and its a good thread for working on the eight, so keeping it alive with your troubles is fine by me. I'd love to have threads that have all the good info in them that this one does.

Yep 250K x 2. I might be screwed. I may take a chance here. http://www.sansui-parts-shop.com/index.php?page=details&prod=283&cat=312&group=28

 

[DCinDC]

Buy one of those chinese fake blue alps pots off of ebay. Make SURE it has 8 terminals, not 6. About 5 bucks.

 

[Zekeman]

Thanks for this thread!! I restored / recapped my Eight back in the fall of last year. I just pulled it out to run it as I was considering selling it. I noticed a nasty POP! upon switching the selector from Phono to FM Auto. After reading this thread I replaced C7027 and C7028 on the preamp board (I had NOT replaced these previously) and reflowed the large solder joints for this boards connecting wires.....Now the POP is gone!!

I do have a question though....on the power supply board there are several flying saucers and I was never able to determine their proper replacements...CDC8003 as well and the zener diode ZB-1-25....Any advice will be much appreciated!

Thanks...Zeke