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

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

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

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?

"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" 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"

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

jak

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

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.

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

Dave

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