Problem with right channel of Sansui AU-101 solid state amplifier

[Robin]

I was wondering if somebody could tell me how to fix a problem I'm
having with my Sansui AU-101 solid state amplifier.

Since I got the device, I'm having this problem with my right channel.
The left channel works perfectly, but the right one doesn't produce any
sound. When I turn up the volume to the maximum, I can hear some very
soft noise on the right channel.

I think the problem is located in one of the 4 transistors located at
the rear end of the amplifier. When i was trying to obtain the voltage
going through the transistors, i accidentally hit the base of one of
them, and for a few minutes the amp worked perfectly again. :S

As far as i see, the base of all 4 transistors are not connected to the
printboard. It says 'Hitachi 1060D'. Unfortunately i didn't find any
specifications of the (FET?) transistor on the net, nor do I have a
technical scheme of the amplifier.

I hope somebody will be able to tell me how I can find a nice
equivalent for this transistor.

Thanks in advance!
Robin

 

[Dave D]

As far as i see, the base of all 4 transistors are not connected to the
printboard. It says 'Hitachi 1060D'. Unfortunately i didn't find any
specifications of the (FET?) transistor on the net, nor do I have a
technical scheme of the amplifier.

Maybe a 2SD1060? Stating the case style would be a big help here.

http://tinyurl.com/9ldld

Japanese manufacturers often delete the first part of the semiconductor
code, though usually only the 2S part. It's a long shot though, I'm not
convinced this is the same part.

Dave

 

[[email protected]]

The transistor looks the same as the one in the specsheet of the
2SD1060. It's not attached to a cooling element, but i think it must be
capable of transmitting high voltages. The maximum output of the amp is
15 Watts RMS per channel.

I still wonder why the the bases of all 4 transistors aren't connected
to the circuit board. Does the metal part with the screwhole function
as a ground-base?

 

[Asimov]

"Robin" bravely wrote to "All" (09 Dec 05 05:23:11)
--- on the heady topic of "Problem with right channel of Sansui AU-101 solid
state amplifier"

Ro> From: "Robin" <[email protected]>
Ro> Xref: core-easynews sci.electronics.repair:350799

Ro> I was wondering if somebody could tell me how to fix a problem I'm
Ro> having with my Sansui AU-101 solid state amplifier.

Ro> Since I got the device, I'm having this problem with my right channel.
Ro> The left channel works perfectly, but the right one doesn't produce
Ro> any sound. When I turn up the volume to the maximum, I can hear some
Ro> very soft noise on the right channel.

Ro> I think the problem is located in one of the 4 transistors located at
Ro> the rear end of the amplifier. When i was trying to obtain the voltage
Ro> going through the transistors, i accidentally hit the base of one of
Ro> them, and for a few minutes the amp worked perfectly again. :S


This touching the base and amp works again behaviour may be due to a
couple of things. The first cause may be a dry electrolytic capacitor
that becomes momentarily "healed" by the probe's introduced stray
static.

Another cause is also related to the stray static but unfortunately
may be a broken internal connection inside the semiconductor device.
Sometimes pressing the terminal in with a slight pressure or twist
will confirm the defect is internal.

However, the really good news is that in 99% of cases I've seen the
"works when I touch it with probe" behaviour relates to dry electros.



Ro> As far as i see, the base of all 4 transistors are not connected to
Ro> the printboard. It says 'Hitachi 1060D'. Unfortunately i didn't find
Ro> any specifications of the (FET?) transistor on the net, nor do I have a
Ro> technical scheme of the amplifier.

Ro> I hope somebody will be able to tell me how I can find a nice
Ro> equivalent for this transistor.

Ro> Thanks in advance!
Ro> Robin

Typically these require exact replacements not equivalent subs. There
are just too many unpredictable factors that went into the device
choice when the amp was designed. In fact transistors are often made
specially for a specific design. This explaines why there are so many
transistor types!

A*s*i*m*o*v

.... If you don't know what leever "A" does then you better leever "B"

 

[jakdedert]

The transistor looks the same as the one in the specsheet of the
2SD1060. It's not attached to a cooling element, but i think it must be
capable of transmitting high voltages. The maximum output of the amp is
15 Watts RMS per channel.

I still wonder why the the bases of all 4 transistors aren't connected
to the circuit board. Does the metal part with the screwhole function
as a ground-base?

I suggest you look at the repairfaq.org listings and educate yourself a bit.

jak

 

[Dave D]

The transistor looks the same as the one in the specsheet of the
2SD1060. It's not attached to a cooling element, but i think it must be
capable of transmitting high voltages. The maximum output of the amp is
15 Watts RMS per channel.

I still wonder why the the bases of all 4 transistors aren't connected
to the circuit board. Does the metal part with the screwhole function
as a ground-base?

Bases? The metal tab or body of a audio power transistor is almost
invariably the collector, not the base. I don't recall ever seeing a
transistor where the case is the base.

If only two legs of the transistor are connected then yes, the third must be
made via the body/tab via a screw or bolt. Generally with a TO220 style
case, the left leg is the base, the centre is the collector, which is also
connected to the tab, and the right leg is the emitter.

You say the transistors in question are not connected to a cooling element,
which I take to mean a heatsink. If so, then they are certainly *not* the
output transistors, more likely the drivers.

Dave

 

[Arfa Daily]

Bases? The metal tab or body of a audio power transistor is almost
invariably the collector, not the base. I don't recall ever seeing a
transistor where the case is the base.

If only two legs of the transistor are connected then yes, the third must
be made via the body/tab via a screw or bolt. Generally with a TO220 style
case, the left leg is the base, the centre is the collector, which is also
connected to the tab, and the right leg is the emitter.

You say the transistors in question are not connected to a cooling
element, which I take to mean a heatsink. If so, then they are certainly
*not* the output transistors, more likely the drivers.

Dave

In which case Dave, makes you wonder how the collector is getting connected
.... ?? I think that we have to assume that whatever these transistors are,
only the B-E junction is being used for its thermal characteristics or
something similar. I've seen this sort of thing before, but still usually
connected mechanically to the output heatsink for output thermal
compensation.

It sounds to me as if the poster hasn't got quite enough technical
experience to deal with a fault on this type of equipment on his own.

Arfa

 

[Dave D]

In which case Dave, makes you wonder how the collector is getting
connected ... ??

I'd assumed they were bolted to the PCB, but with no heatsink. I'd like to
see a picture as it's all a bit mysterious.

I think that we have to assume that whatever these transistors are, only
the B-E junction is being used for its thermal characteristics or something
similar. I've seen this sort of thing before, but still usually connected
mechanically to the output heatsink for output thermal compensation.

It sounds to me as if the poster hasn't got quite enough technical
experience to deal with a fault on this type of equipment on his own.

Yes, I agree. I suppose there's worse places for a novice to start though,
like a TV/monitor or a microwave oven!

Dave

 

[Robin]

What you're saying is true. The collector is connected to the tab
indeed. I thought that the part where the transistors are attached on
is made of plastic. But it appears to be alluminium. Sorry, my mistake!

I put a 50Hz signal on the amplifier and I measured the (AC) voltage
going through the transistors. It appears that that 2 transistors have
been used per channel. I switched the transistors from the left to the
right channel, but the problem remained in the right channel. So the
dryed up capacitor theory might be true.

I tried to switch some of the capacitors too; unfortunately nothing
happened. I have been switching quite a lot of capacitors now, without
results.

Since i don't feel like de-soldering all capacitors, i was wondering if
there is a convenient way to test capacitors without removing them from
the circuit. Where should i look first?

All hints are welcome, because this n00b needs some help ;-)

 

[Dave D]

What you're saying is true. The collector is connected to the tab
indeed. I thought that the part where the transistors are attached on
is made of plastic. But it appears to be alluminium. Sorry, my mistake!

I put a 50Hz signal on the amplifier and I measured the (AC) voltage
going through the transistors. It appears that that 2 transistors have
been used per channel. I switched the transistors from the left to the
right channel, but the problem remained in the right channel. So the
dryed up capacitor theory might be true.

I tried to switch some of the capacitors too; unfortunately nothing
happened. I have been switching quite a lot of capacitors now, without
results.

Since i don't feel like de-soldering all capacitors, i was wondering if
there is a convenient way to test capacitors without removing them from
the circuit. Where should i look first?

All hints are welcome, because this n00b needs some help ;-)

Forget about capacitors for now. If you have a cheap set of amplified
computer speakers, attach a probe to them and you can use them as a signal
tracer. All you have to do then is supply a signal into the amp via a CD
player or whatever, go through each stage of the amp and find out where the
signal stops. My guess is a mechanical fault like a bad solder joint, faulty
volume pot, input select switch, speaker in/out switch or headphone jack.

Dave

 

[Hansepans68]

Sansui AU-101

@ Robin


As I'm also owner of a AU-101 I've experienced some problems through the years.

One of the strangest things was that 2 of the final stage 2SC1060 (yes, this is the original type of the used transistor) had a faulty base. By tapping on the transistors, the amplifier
would work for a little while an then gave a distorted signal again.
I replaced all 4 2SC1060's by SGS-Thomson TIP41C's 6 years ago.
The TIP41C is pin compatible with the 2SC1060 and the amplifier doesn't response differently.
Check the 10 Ohm base resistors as well, because one of them was about 20 Ohm when I checked them.

But this is not the problem with your AU-101. Neither are the capacitors.
When I replaced the original 1973 Elna capacitors because I thought they were overdue,
they actually were in a very good shape. So you don't need to replace them.

Still you can replace the supply capacitor with a 10,000 uF/ 63V type and the 2 output capacitors by 4700uF/ 35V types without overloading anything.
My AU-101 is running perfectly with the new bigger capacitors for about 8 years now and gives a better bass response.

As suggested earlier the best thing you can do is to trace where the signal ends, because I also think that it's a mechanical problem you have at hand.

E.g.: check the tape monitor switch, because it failed me on one channel once.
By cleaning the contacts with Kontakt 390 spray ( CRC electro-226 also does the job. Don't use Kontakt 60!!!), it works good for several years.

Best thing to do is to clean the speaker switch contacts as well.

I found the service manual of the AU-101 for free at hifiengine.com
You only need to register (also for free) and you can download the manual easily.

Greetings, Hans