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Sansui AU-217 repair

MiauwMaster

MiauwMaster

Member
Hello everyone,

This being my first post here i'm hoping not to be an idiot in my questions. Also, I'll try to post something about me asap. My problem though:

I have a Sansui AU-217 (as you might have guessed by the post title), bought it secondhand a while back and it looks near mint.The sound was really nice, but the right channel always seemed to be a bit softer(lower volume) then the left. A few days ago it started crackling and popping in the right channel so I immediately disconnected my speakers (Mission 732) and measured the DC on the speaker terminals as I suspected this might be the problem.

I turned the amp on, without anything connected, everything at 0, and let it warm up for about 5 minutes.
On the left channel, which is sounding really nice, I measured between -5.3Mv and -7Mv (meter set to 200Mv scale)
On the right channel however it went from -2Mv to sometimes even 80Mv.

I know a little fluctuation is quite normal but the right channel does not look normal to me.

Now, this is my first time to attempt to repair a amplifier but I'm no stranger to soldering and (high)voltages.
My only question is, which parts to replace first? I am in possession of a service manual so that should at least make it easier to find the parts. I live in the Netherlands, so the Sansui-Parts-Shop is where I plan to get my parts I guess.

Long post, I know. Any help is greatly appreciated!
 
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MiauwMaster said:
so the Sansui-Parts-Shop is where I plan to get my parts I guess.
Click to expand...

More like Farnell and RS Components, Sansui Parts Shop is for Sansui specific parts, not so much general usage parts.

Less local but with much larger ranges of parts, Mouser and Digikey (in the USA).

May I suggest you do a lot of reading of restore threads here on AK, you'll soon pick up how we deal with parts issues.
 
Just FYI, M means Mega, m means milli. If you had 80 MV offset on that amp, you would be dead by now.

Look at the power amp board - IC1 and IC2 are 2SA798. Famous junk transistors. These go bad and they are what causes bad offset. Replace these with matched pairs of KSA992 transistors. Google it, we've been over this a million times on AK.
:)
 
inductor said:
the pre amp transistors cause lots of problems, i would replace them, and the ones in the tone section
Click to expand...

Thx, I'll definitely look into that.

Hyperion said:
More like Farnell and RS Components, Sansui Parts Shop is for Sansui specific parts, not so much general usage parts
Click to expand...

I was assuming I needed Sansui specific parts and as they were local. But ill check the others too!

ZOOM said:
Just FYI, M means Mega, m means milli. If you had 80 MV offset on that amp, you would be dead by now.

Look at the power amp board - IC1 and IC2 are 2SA798. Famous junk transistors. These go bad and they are what causes bad offset. Replace these with matched pairs of KSA992 transistors. Google it, we've been over this a million times on AK.
:)
Click to expand...

Lol I switched mV capitals. I knew that. Just didn't check before posting, thx for reminding me though. Would not have liked MegaVolts on there hehe. Would that make it a GigaWatt amp? :p

Ill get these IC's switched asap (after next week) and check back on my progress!
 
Hm I'm finding KSA992FBU and KSA992FTA and I can't seem to find any difference between them. Also I can't find matched pairs but all state the same values. My multimeter can check these things so I could just order a few more and match them as close as possible myself as they are quite cheap. Would that work or am I talking nonsense :p.
 
PLUS!!!

Replace VS 01,01) VD1212 with IN4148TA before they blow up your amp. You need 4 of these, wire two in series for each channel of the amp.
Digikey
http://www.digikey.com/product-detail/en/fairchild-semiconductor/1N4148TA/1N4148TACT-ND/1532747

And replace the fusible resistors while you're in there.

Fusible Resistors

R 39, 40, 41, 42) 220 Ohm, 1/2 W
Digikey
http://www.digikey.com/product-detail/en/NFR25H0002200JR500/PPC220BCT-ND/614251


R 43, 44, 45, 46) 6.8 Ohm, 1/2 W
Digikey
http://www.digikey.com/product-detail/en/NFR25H0006808JR500/PPC6.8BCT-ND/614269
 
MiauwMaster said:
Hm I'm finding KSA992FBU and KSA992FTA and I can't seem to find any difference between them. Also I can't find matched pairs but all state the same values. My multimeter can check these things so I could just order a few more and match them as close as possible myself as they are quite cheap. Would that work or am I talking nonsense :p.
Click to expand...


The last letters are package information. One is BU Bulk and TA is Tape Real for insertion machines. Look at the spacing you need on the pins and order the one that is close to the dimensions you need.

Look at the drawing at the top of the data sheet.
http://www.mouser.com/ds/2/149/KSA992-889331.pdf
 
SoundOfSound said:
The last letters are package information. One is BU Bulk and TA is Tape Real for insertion machines. Look at the spacing you need on the pins and order the one that is close to the dimensions you need.

Look at the drawing at the top of the data sheet.
http://www.mouser.com/ds/2/149/KSA992-889331.pdf
Click to expand...

Thx. Unfortunately I'm afraid I'll have to order somewhere closer to home as mouser and digikey ask over $20 shipping on total parts worth $5 or $7 and Conrad.nl (dutch supplier) only about $5 shipping. Do the parts have to match on absolutely everything? the IC's I can find but the resitors are 0.6w instead of 0.5w and the Temperature Coefficient is 50 instead of 100. Sorry if these questions are a bit noobish but I'd rather not fry my amp after hard work of soldering in replacement parts. I'm guessing it wont matter too much but I'd rather be sure!

My eternal thanks to everyone! ;)
 
Also, while I'm at it, would it make sense to replace the bias trim pots ( 470Ohm original white single turn) with Bourns 3296(500Ohm) multi-turn? There's a bit difference in ohms but I don't think It's too much.
 
RS-Online should have the transistors & fusible resistors (you should replace fusible resistors with fusible resistors, if possible), or Cricklewood electronics. I've always found Conrad expensive & limited parts ranges.
Not sure on international shipping, but UK parts should all be ca. 20% cheaper lately.....
 
Goldie99 said:
(you should replace fusible resistors with fusible resistors, if possible)
Click to expand...

My impression of the AK community is that they regard new fuse resistors as a waste of time, certainly so in my case. Their construction has improved over the years, but most replace any found with standard metal film resistors of the same wattage.
 
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It would be a good idea to do some actual troubleshooting here to find out which circuit the problem is in and which part is bad. If you have a set of speakers you don't care about, connect them to the amp and listen for the noise. Then turn the volume down and see if the noise goes away. If not, the problem is in the power amp, not the preamp and you are wasting your time replacing preamp parts.
Next, buy a can of freeze spray and spray a small amount on each of the small black plastic transistors, one at a time. If the noise gets worse or better, that's the bad transistor. To protect your speakers during this test you can connect a 100 Ohm resistor in series with the speaker on the bad channel. The problem is most likely a noisy transistor and spraying it with freeze spray usually produces a lot of noise.
 
Hyperion said:
My impression of the AK community is that they regard new fuse resistors as a waste of time, certainly so in my case. Their construction has improved over the years, but most replace any found with standard metal film resistors of the same wattage.
Click to expand...

Generally, I might agree, but most of the fusibles I've been looking at lately have been spec'ed as fusible & flameproof (e.g., 70's / 80's Sony ES amps) - and while the majority of metal films will fail 'open', they are not all flameproof, so where I find them spec'ed as flameproof as well, then I tend to go for fusible / flameproof replacements, where possible.

Having said that, I'm not sure what the original Sansui AU-217 spec's were, e.g., if they included flameproof, so maybe standard metal film are sufficient.
 
dr*audio said:
It would be a good idea to do some actual troubleshooting here to find out which circuit the problem is in and which part is bad. If you have a set of speakers you don't care about, connect them to the amp and listen for the noise. Then turn the volume down and see if the noise goes away. If not, the problem is in the power amp, not the preamp and you are wasting your time replacing preamp parts.
Next, buy a can of freeze spray and spray a small amount on each of the small black plastic transistors, one at a time. If the noise gets worse or better, that's the bad transistor. To protect your speakers during this test you can connect a 100 Ohm resistor in series with the speaker on the bad channel. The problem is most likely a noisy transistor and spraying it with freeze spray usually produces a lot of noise.
Click to expand...

Very good idea. I've checked what you've mentioned already just forgot to tell about it. The problem is in the power amp. the noise is the same not matter what I do to the pre-amp section regarding volume, source and equalizing. I'll try the freeze spray when I can. Will be after next week though.
 
Goldie99 said:
Generally, I might agree, but most of the fusibles I've been looking at lately have been spec'ed as fusible & flameproof (e.g., 70's / 80's Sony ES amps) - and while the majority of metal films will fail 'open', they are not all flameproof, so where I find them spec'ed as flameproof as well, then I tend to go for fusible / flameproof replacements, where possible.

Having said that, I'm not sure what the original Sansui AU-217 spec's were, e.g., if they included flameproof, so maybe standard metal film are sufficient.
Click to expand...

OK fair enough, either way is personal choice, those fuse resistors get such a bad press people are pretty wary of them.
 
Goldie99 said:
RS-Online should have the transistors & fusible resistors (you should replace fusible resistors with fusible resistors, if possible), or Cricklewood electronics. I've always found Conrad expensive & limited parts ranges.
Not sure on international shipping, but UK parts should all be ca. 20% cheaper lately.....
Click to expand...

wow.. RS-Online makes me order resistors by the 2000. That's a bit excessive :p.
 
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