Problem Sansui AU505

Hi everybody, I have a problem with a Sansui au505 I bought on eBay... I got it arrived last Saturday: first thing I notice is that the light is not working; also, the mic and phone plug do not click when a jack is inserted. So I decide to open it and I find out that both of the female plugs for the jack are broken and the lamp is broken too. Nevermind, I go to RadioShack and on Sunday I replace the parts. Everything works fine, and I listen to the amp for almost a couple of hours, sounds really good. Today, after a week of work, I switch it on again and it works wonderfullyfor almost half an hour, but then it starts making a very annoying white noise even at volume zero and very little sound comes out of the speaker even at 10 volume... :( What happened? what can I do to fix it?

Thanks for your help,
Andrea
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Hi Andrea.
This amp is very old. Perhaps 1971. It is full of electrolytic capacitors, a lot more than modern amplifiers and these are not everlasting. Over time and the heat inside the case, they dry out and lose their quality completely or even short out, explode etc.

When you buy old electronic equipment, this is what is lurking and causes failure and collateral damage to other parts such as transistors, resistors, even small fires, some period after powering it up again after so many years of neglect. A technician would not simply apply power, they would use a current limited power source or simply replace all capacitors before even testing it.

If there is no sign that much has been replaced, you need to download the schematic, find the BOM and make a shopping list for the electrolytic capacitors. It won't matter that you have to buy higher voltage parts than shown or even higher capacitance up to 60% more rating, as new parts are smaller. However, never use less than original voltage or capacitance ratings. Don't buy cheap, unknown brands just because that's all you can buy locally. You may regret that and the sound may not be quite what you were hoping for. There are regular quality, industry standard and boutique parts but industry standards like Panasonic, Rubycon, Samwha, Nichicon, Nippon Chemicon. etc in appropriate grades will be fine.

When ordering, check the outside dimensions and type (axial or radial leads) that will fit the space and the lead spacing matches closely or you won't have much success.
Note, these are polarized components, don't confuse, lose, or mix up the correct orientation of positive and negative leads. Mark as (+) or (-) what you see on the cap onto the PCB, if there is no printed layout on it. Do this before removing the cap. Only remove the next 1 or 2 caps as you replace them, to avoid losing your way.

You need to check how to do many things here, beyond one answer and this is not a quick fix like changing a fuse. It's restoration work and when you have finished, don't simply power up until you can test that it is safe by making up your own current limiter; an incandescent 60W lamp in series with the active mains connection to the amplifier. It's call a bulb tester and you can find details by searching this forum.

This is important wiring, critical to your safety, so if you can't wire this up using even a table lamp with a suitable mains socket and wiring, don't proceed.

Hopefully, the amplifier will still be OK after this but recheck for obvious burnt components, signs of heating etc. as you proceed. You are at least at a point where measurements could be meaningful and you can troubleshhoot the amplifier, if necessary.
 

frusciante89

Member
2013-02-03 12:28 am
Ok, thanks for your great answer!... I have more info about the problem: I tried with other speakers an also with earphones, and the problem is still there. Anyways, when I turn the amp on without any input, I notice that the right channel has no hum, whether the left one is really noisy; however, sound is coming out extremely low and distorted from both channels.
Do you think there's a way to spot the damaged capacitor? Also, how much will it cost me to replace all the capacitors? Sorry for these silly questions but I'm new in the field...

Thanks for your help,
Andrea
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
There could be many problems with your amplifier, apart from the capacitors. Using it in that condition, as I explained, is sure to cause more damage that will not only increase cost to you but also make repairs very difficult to carry out, even for a technician. Don't attempt to use it!

It is not a case of which capacitor is damaged when, if they are original parts, all will be damaged to some degree. It is not worth anybody's time to argue what may or may not be faulty. Replace them all if you want a usable amplifier with some chance of it lasting for a few more years.

I would like to add to the first reply that you should really increase the values of the large output capacitors, C819,820 to 3,300-4700 uF for cleaner bass with a little more depth.

When that is done, you can look at the condition of the transistors but technicians would probably have tested them too, perhaps whilst waiting for the capacitors to a arrive, in case the output stages have already been fried by trying to use the amplifier when the capacitors have failed. Normally, they would also be removed to test properly if there was some doubt there.

Be prepared to spend a lot of time and money here as it could cost about $50 US on caps alone, plus you will need good electronic soldering equipment with a fine tip of 1-1.5 mm, a reasonable quality digital multimeter, small tools like screwdrivers with Philips and plain blades, long-nose pliers and side cutters. You may also need sundry materials like PVC sleeving or heat-shrink tubing to insulate axial leaded components, if any.

Transistors may not be expensive but the cost of postage, etc. can be high. Fakes are everywhere but there is no point buying fakes if you go to the trouble of repairing the amplifier properly. Use guaranteed sources and just because you see nice pictures on Ebay, doesn't mean anything. Parts may "work" but not properly if the chips inside the cases are nothing like the correct part, and that is a common experience of unwary Ebay clients.

So far, I think you will have to agree there.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Hi John, just noticed your post in this old thread. I'm not sure what you mean by system-B but you can start by downloading a very basic service manual which you can sign up for free here: Sansui AU-505 - Manual - Solid State Integrated Amplifier - HiFi Engine

Its a small power amplifier and the circuits are not complex but you still need to test the basic condition before looking further into transistor damage etc. To do this, it has to be powered but don't just connect mains power to see what happens because there are no protection circuits on such old designs so it will only make any problems worse and may even blow fuses if they aren't already blown.

It's safest to use a lightbulb limiter a.k.a. dim bulb tester of 40-60W incandescent type only, to protect the amplifier from further damage and test whether there is a serious problem first. You can make one from the many simple plans you find just by googling the titles - but take great care with anything wired to the mains. Unfortunately, death is permanent so don't take risks, intended or just ignored :nod:

If there is no obvious problem as shown by a continuous glow from the bulb, you can proceed by replacing all the electrolytic type capacitors (about 10 on the F1266 power board and also the large C101 power supply capacitor, much as said in my previous post, 5 years ago :) You don't need special quality caps - just genuine reputable brands and some, like the output capacitors would be better if increased in value as I said before. Replacements will also be much smaller in size than the old caps but fit like for like voltage and capacitance values but if you need to use different values, always choose use the next size up in the range for either or both ratings.

When you have good caps correctly wired in, you can check the voltages shown on the schematic and then continue by testing transistor voltages to see what may have failed there - but let's do the essential part first. Whilst you are thinking about parts, consider replacements for the output transitors - they may not be replaceable and you may have to fit TO220 plastic types instead, if they are damaged so check for availability or substitutes for those hard-to-find old components as soon as possible.
 

Johnsimon

Member
2018-04-18 8:02 pm
Thank you Ian Finch. It has four outputs, two in system A and two in system B. There are only one in system A and one in system B. There are two burnt 2SD188 (TO) transistors, corresponding to the outputs.
I can not find these transistors here in Brazil, what would be the equivalent of them?
Sorry for typing errors, I'm using google translator.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
.... There are two burnt 2SD188 (TO) transistors, corresponding to the outputs.
I can not find these transistors here in Brazil, what would be the equivalent of them?.....
If you only need help to buy parts, you'll know that there are many posts and replies here and elsewhere, asking for the same transistors. The amplifier is nearly 50 years old and I don't believe that there are any genuine equivalent Japanese TO3 transistors that are widely available so you will likely need to use substitutes. There are fake parts which may work but you won't know for how long or whether you could buy cheaper and better substitutes elsewhere - at least knowing what they are.

The primary characteristics are 100V Vceo, 10A Ic, 10 Mhz Ft transistors and most standard US type audio transistors that would work are only 1-4 MHz Ft which may be OK but not ideal. However, the more important factor in buying audio transistors is that are genuine or genuine substitute parts but not fake parts of any type. In the global market, that is hard no know when sellers don't know or care about old parts for restorers. Buy from reputable sales agencies, not internet re-sellers or dealers.

TO3 audio type transistors are expensive so take that as hint when shopping. The suggested types will probably work fine, provided you first check that driver transistors 2SC875, 2SA532 are also OK. Otherwise, you may get repeat failures and further damage. I notice that a lot of people simply fit low grade 2N3055/MJ2955 because they are dirt cheap and whilst these may work, they are likely fakes and take out the drivers too when they also fail.

In Brazil, You should be able to buy these complementary types from On-Semi agencies such as Arrow and Farnell Element 14: MJ21194/MJ21193, MJ15015/MJ15016. Higher voltage complementary pair audio types in the On-semi MJ150XX audio range may also work OK. A "G" suffix to their part number only signifies lead-free conformance. You may see Generic US spare parts NTE87 and NTE88 also suggested as substitutes but I have no experience or idea of where they may be bought in Brazil: http://www.nteinc.com/specs/10to99/pdf/nte87.pdf

Again, as you need to substitute, you must use a dim bulb tester to prevent damage on test unless you really know what you are doing and don't need advice.
 
Last edited:

968driver

Member
2008-05-17 5:37 pm
Hi everybody, I have a problem with a Sansui au505 I bought on eBay... I got it arrived last Saturday: first thing I notice is that the light is not working; also, the mic and phone plug do not click when a jack is inserted. So I decide to open it and I find out that both of the female plugs for the jack are broken and the lamp is broken too. Nevermind, I go to RadioShack and on Sunday I replace the parts. Everything works fine, and I listen to the amp for almost a couple of hours, sounds really good. Today, after a week of work, I switch it on again and it works wonderfullyfor almost half an hour, but then it starts making a very annoying white noise even at volume zero and very little sound comes out of the speaker even at 10 volume... :( What happened? what can I do to fix it?

Thanks for your help,
Andrea
I have serviced a lot of Sanui amplifiers from the seventies.
Most common problems are dirty switches and noisy potmeters.
I did not find bad electrolytic capacitors that much, even after 45 years.
Except the one in the power-on timing delay circuit.
I would never replace all elco's at once and without any diagnose or visible damage.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
That post was 5 years ago but when output transistors fail, even when protected by an elco of only 1,500 uF, you know that something a lot worse than a dirty switch or pot. is the problem. Perhaps it's a climate issue but I've seldom encountered consumer devices where caps in a small power amplifier or power supply are still acceptable by ESR measurement, after 40 years.

Unless a repairer has the experience, knowledge and equipment to make judgements on acceptable quality, it is much safer for newbies with a problem to just replace inexpensive consumables like most of these caps. Buying the equipment, doing the tests and posting results and limits for every cap here will be more painful than simply replacing them.