Can I fix a Sansui au X701?

[Infernosaint]

Hey guys, I've been looking around here for some time, and now I have a reason to post here.

I have an old x701 that I got from my uncle, been using it a lot since I got it.

Thing is, it won't turn on anymore. The protection light just keeps blinking. I have unplugged every single cable, inputs and outputs, and no change. So I figured it would have to be internal.

I have attached some pictures of some of the insides. The 2 big caps seem to have been leaking at some point, could this be the problem?

Also, what can I use to clean the PCB without damaging any components? Like a toothbrush and some chemical?

Thank you very much

 

[larryderouin]

If the "leak" is brown and HARD, then it's probably the glue Sansui used on larger caps to hold them in during soldering and transport to US. It needs to be removed as it's somewhat corrosive to the internal parts.

The reason the light is blinking is , it's in protection, meaning there is SC Voltage in the amp section that isn't supposed to be there. It can be caused by a lot of things, but the most common is bad caps in the amp board, a shorted driver transistor, or a blown output transistor.

cleaning. Simple Green, Toothbrush and 1-1/2" chip brush, Hot Water. Final Rinse with 91% alcohol to displace the water in crevices. Let dry 2-3 days with a fan on it.

Larry

 

[Infernosaint]

The brown seems to be dirt that has stuck to the substance, and it comes off with a swipe of my finger.

Can I use any All purpose cleaner?

Any idea where to begin, trying to find the bad part?

 

[Hyperion]

Congratulations - you have a great amp there.

Well, it is a bit dirty, stuff dripped on top of the amp and onto the chassis all around the 2 biggest capacitors and transformer.

The 2 large caps in the middle of the PCB just might have been leaking - but more likely this is discoloured glue used to secure them to the PCB.

The failure to 'turn on' is caused by the protection circuitry operating (probably correctly) to prevent an excessive DC voltage at the output being applied to your speakers - which would otherwise damage them.

The DC voltage can be adjusted - there are 8 trimmers on the main board - 4 for Bias and 4 for offset (I think these are labelled as such). You need to get hold of the offset adjustment procedure (quite simple) and see if you can null out the voltage holding the protection circuit on.

The bias setting procedure is fairly simple but you need to understand that when doing it - one slip and you could seriously damage the amplifier - AND, get the adjustment wrong = same result.

I will say that if you can't null this voltage out it needs the attention of a good tech as these amps are complex - and definitely not for the novice to attempt.

Well worth almost any effort / cost to get it going.

 

[Infernosaint]

Yeah, I already got the pdf about adjustment for this model, but I have never done something like this. Any starters guide to get the idea? I'm pretty sure I have my multimeter around.

I'll start by cleaning up the PCB as described, and then check back. should I try to get the brown stuff off?
Also, should I get the PCB out of the amp, to clean it properly?

 

[Hyperion]

Yeah, I already got the pdf about adjustment for this model, but I have never done something like this. Any starters guide to get the idea? I'm pretty sure I have my multimeter around.

I have just thought - you are going to need to read the schematic and be able to identify the speaker output BEFORE the speaker relay. (You will read zero volts at the speaker terminals - and thus NOT be able to adjust the offset by reading the voltage here). Do you think you can do this? - this will be somewhere near those 4 wire coils on the pcb. The offset pots are the 3 blue ones & one black, 2 to the top right, and 1 blue & 1 black to the top left, of your pic, the bias pots are the row of 4 black ones across the PCB in your pic.

I'll start by cleaning up the PCB as described, and then check back. should I try to get the brown stuff off?
Also, should I get the PCB out of the amp, to clean it properly?

I would recommend you do not try to remove the brown stuff - yet - as there is too much danger of damaging something. And anyway to clean it off properly you will need to remove those big capacitors on the PCB. Do not try to remove the PCB from the amp.

I have one of these amps as well - but have not got around to reconditioning it yet - it works :yes:

 

[Infernosaint]

So, I am not going to follow the steps of the adjustment guide i found here?

The last page of this document:
http://www.scribd.com/doc/57523246/Sansui-AU-X701-X901-Service-Manual
Is what I found.

If I am not going to follow this, then no, I'd need some guidance to do it. I know my way around electronics, but I've never looked at an amp circuit like this.

 

[Hyperion]

So, I am not going to follow the steps of the adjustment guide i found here?

Unfortunately the offset is not just 'in need of adjustment' it is way off - causing the protection circuit to disconnect the usual point for measuring it - namely the speaker terminals. I am sorry I neglected to realise this in my earlier post(s) - and may have misled you as to how easy this may be as a result.

So, not as simple as following the adjustment procedure in this case I am sorry to say.

I tried your link - but no go (our firewalll has blocked it) am at work at the moment.

 

[Infernosaint]

I see. Would it be a lengthy procedure, or could I possibly be guided through it?
If anyone would be willing to do it step by step, I could take pictures and post measurements for each. Anyway, It'll be a few days, so I can let it dry, when I'm done cleaning it.

I'd also really like to start getting into this stuff, but I realise that it might not be the best place to start

 

[Hyperion]

OK, well although a complex amp, the adjustments, in this case are no more complex than any other really.

However if it does have a fault causing the protection circuity to activate - that's where the fun starts. There is nothing to suggest your one does have a fault thus far and it is more likely to be the offset adjustment out of kilter.

I don't have the service manual to hand at present - when I am at home I can identify the point(s) you need to measure for each channel when doing the adjustments.

I can also tell you that the published bias adjustment procedure is 'pants' and there is a much simpler way to do it.

However if we find there IS a fault causing the protection to be triggered - then I will advise taking it to a tech - I think I can get you to that point.

For some tips on cleaning - have a look here http://www.audiokarma.org/forums/showthread.php?t=258899

 

[Infernosaint]

Thanks a lot!

Well, it was working a few days ago, then it would go into protection. Then after a while, I could switch it on just fine again. Then later it would stop again. I figured something might be getting too hot, or it's general condition might be the cause, so I dusted it off properly, but in the end, it switched to protection for good.

I dunno if that helps.

But thanks a lot, I do hope it can be fixed without too much hassle.

I'll clean the dirty PCB as much as I can without removing it.

 

[Hyperion]

Thanks a lot!

Well, it was working a few days ago, then it would go into protection. Then after a while, I could switch it on just fine again. Then later it would stop again. I figured something might be getting too hot, or it's general condition might be the cause, so I dusted it off properly, but in the end, it switched to protection for good.

I dunno if that helps.

But thanks a lot, I do hope it can be fixed without too much hassle.

I'll clean the dirty PCB as much as I can without removing it.

Ok, interesting - we'll see if we can get it out of protection and take it from there

 

[eradoncic]

So, I am not going to follow the steps of the adjustment guide i found here?

The last page of this document:
http://www.scribd.com/doc/57523246/Sansui-AU-X701-X901-Service-Manual
Is what I found.

If I am not going to follow this, then no, I'd need some guidance to do it. I know my way around electronics, but I've never looked at an amp circuit like this.

Hi, I just saw this thread, and I hope this can help:

The DC blocked relay should be released at first.
As Hyperion said, you should first do rough adjustment, and before the relay.
Look carefully your first picture attached on your post #1...toward the left upper corner on that picture, you can see the 5-pin plastic terminal, very easy accessible for DMM od DC voltmeter. Those are predicted for quick (industrial) and easy adjustments.
Connect the DC voltmeter between "out" and "out", on the each channel (those two points are derived vrom NPN-PNP emmiters of each channel)....adjust at minimum possible. Do it for both channels
The adjustment trimmers are located on the power amp PCB left and right, on the corners.
They are two: HOT-COLD and COLD - EARTH

Pins 1 and 4 should be adjusted with hot-cold one
If those values are OK (<500mV DC), then check between pin 1 and 3, and pin 4 and 3 (Ground) and, also adjust to minimum using the second trimmer (COLD -GND)

At the time of less than 500mV, the relay should be released, and then proceed as per manual, if you want.

When the relay is released, you may switch the DC measuring points to speaker terminal(s); then,
- run the amp at medium power for 1/2 hr or so, listening some music or radio. Make sure it is warmed up, simply touching the cooler
- put the volume at minimum, turn off any input
- readjust DC; adjust bias. It should be measured on the both lateral pins of the big rectangular emitter resistors (but also on the plastic terminals I mentioned, using pins E and G; much easier access is on the emitter resistors, though).
- Obtain DC 17-19mV, adjusting the four trimmers (1kOhms) which are in line, one per pair of output transistors (8 of them, they are under PCB) as per service manual
- recheck and readjust again DC,
- leave amp without any signal for 1hr or so, recheck, readjust
And that's it

The X701 is otherwise very durable and well made integrated, it is rare to have any failure as previous models.
But...it is incredible how bad trimmers it has, and they are usual culprits for activation of protector mode

 

[Hyperion]

Brilliant ! ^^^there you have it^^^ from the master.

I hadn't checked where those 5 pin connectors go to - now I know (thanks Erden) :thmbsp:

 

[eradoncic]

Thanx for the kind word John,
I have the same model since 1988. and I really know it as my pocket...in my hand (as a scholars at the time), this amp survived numerous parties, driving disaster-type speakers etc, and never failed. Never.

Brilliant ! ^^^there you have it^^^ from the master.

I hadn't checked where those 5 pin connectors go to - now I know (thanks Erden) :thmbsp:

 

[Pepa]

...
Look carefully your first picture attached on your post #1...toward the left upper corner on that picture, you can see the 5-pin plastic terminal, very easy accessible for DMM od DC voltmeter. Those are predicted for quick (industrial) and easy adjustments....

That's all right if you have a steady hands,...but if you do not,then you can make a cable like this...from USB cable for pc motherboard

I made a couple of these cables and easily pulled them out of the housing and then monitored dc and bias on my B-2102 a whole afternoon

The entire procedure was made several years ago,with great online help of Erden,of course

 

[eradoncic]

That's all right if you have a steady hands,...but if you do not,then you can make a cable like this...from USB cable for pc motherboard

I made a couple of these cables and easily pulled them out of the housing and then monitored dc and bias on my B-2102 a whole afternoon

The entire procedure was made several years ago,with great online help of Erden,of course

:tresbon:
very good accessory, really.
I was just a bit more concentrated to make troubleshooting easier, and forgot such things.
Nice to see you here, Pepa:thmbsp:

 

[CDFixer]

When you measure those points you have power supply voltage on those points you have problems in the output section, probably fuse resistors that have opened.

 

[Infernosaint]

Hey guys, I'm sorry to have gone like this. I cleaned it, it worked again, and I kinda forgot about it.

Now I would really like to try adjusting this as well as I can, but I really have no knowledge on amps. I know simple electronics, I can solder, and I can disassemble stuff

Should I just follow the adjustment guide I linked? Any specific parts of it?

And would there be any components worth replacing at this point? I would like to get this running as good as possible.

Thank you,

Infernosaint

 

[Infernosaint]

Hate to have to bump like this.

So, the amp as per my previous post has been working fine for a long time, and then yesterday, started going into protection again. But this time, it changes for a period of time, then works again for a period. So, here I have a chance to try and adjust the voltages while the amp actually works and turns properly on.

Where do I begin?
I have this document: (the last page) http://www.scribd.com/doc/57523246/S...Service-Manual

I need to know which points to measure between, and what I should be adjusting it to.

there's diagrams in the document, and there's the images in my original post, if you want to circle the points for me.

Thanks alot again, everyone.