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Quad Sansui problem; help???

Betomon said:
Ok guys about the cardboard... I first showed it in post 92. Here's the pic
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I probably did get a little carried away yesturday :/ My apologies.

I had the multimeter and was trying to test bias and DC I forgot when in protection it dosent show through the speaker terminals :D

So I'll test with the phono plug shortly and report back.

Also, after it was powered on and running for... i'd say maximum of a minute the heatsinks were very cold on the back. BUT, the little sanyo D315d transistor on the pre power supply board was warm.. not so hot that I couldnt touch it, but it was warm indeed.. I thought I should mention that.

Thanks guys :)
Click to expand...

Measure the bias current........

You say you were tying to measure the Bias, how were you trying to measure it?
Rail fuses need to be pulled and your meter in current measuring mode needs to be put across the fuse terminals to get your bias current reading........

Do this before the DC offset....
 
DC Offset:

FL: 55.1
FR: .01
BL: .08
BR: .10

Bias.. I only got 0s.. nothing on any of them with the multi set on 20m.
I tried adjusting VR04 while doing the front left fuse check for bias and it never changed from 0. Also, I thought I had the wrong setting.. so I tried others in the amps section but always got 0 (strangely enough BackLeft got 4.2 under the measurement "1.5V(4.0mA) 9V(25mA)."

So i notice FL is high, but whats the meaning of 0 bias??
 
Betomon said:
DC Offset:

FL: 55.1
FR: .01
BL: .08
BR: .10

Bias.. I only got 0s.. nothing on any of them with the multi set on 20m.
I tried adjusting VR04 while doing the front left fuse check for bias and it never changed from 0. Also, I thought I had the wrong setting.. so I tried others in the amps section but always got 0 (strangely enough BackLeft got 4.2 under the measurement "1.5V(4.0mA) 9V(25mA)."

So i notice FL is high, but whats the meaning of 0 bias??
Click to expand...

Well!! I suppose the FL offset might just be enough to trigger protection mode. The rest look good. I'm afraid I don't understand what you are doing when you are measuring bias. It is like Kevin said. You can read about how to do it in the service manual, also available from HIFI Engine.
 
Betomon said:
DC Offset:

FL: 55.1
FR: .01
BL: .08
BR: .10

Bias.. I only got 0s.. nothing on any of them with the multi set on 20m.
I tried adjusting VR04 while doing the front left fuse check for bias and it never changed from 0. Also, I thought I had the wrong setting.. so I tried others in the amps section but always got 0 (strangely enough BackLeft got 4.2 under the measurement "1.5V(4.0mA) 9V(25mA)."

So i notice FL is high, but whats the meaning of 0 bias??
Click to expand...

What are these DC offset figures?? mV, V, kV, you need to be specific......DC offset is measured in MILLIVOLTS........

If that FL reading is VOLTS were are in trouble.......

the meaning of no bias means there is no current flowing through the output transistors.......
 
I was measuring the DC in volts. All set on 20V except for FL which i had to set to 200V.

The bias I was measuring like the manual said.. I got nothing. But i'll double check
 
Trnsfmr said:
You probably have a high voltage on the left front output, which is putting the whole thing in protection. Interesting that it doesn't burn a fuse. sounds like we are back to the way it was when you got it.
Click to expand...

Yes at the beginning the front left was out as well. But, unlike the beginning, I could hear the headphones fine. (Although I cant remember if I ever heard the front left...).


Also.. when I turn it off the VUs spike pretty hard, the front left spiking the hardest (almost all the way right).

And for some reason my BR bulb is out now :headscrat :grumpy:
 
OK I took out and unplugged the Front driver board.. then turned it on.


No more protection... little test speaker sounded out of the rear right channel, while my multimeter tested DC offset on left channel (80 - 95 mV)

Speaker sounded really scratchy and lots of static/noise from a clean music source input (on AUX). Also pulls in FM but it sounds the same.

According to the manual 80 mV is still high right?


UPDate: Well I was able to adjust them to about 12-18 mV.. the VR1 (BL) was very hard to get low.. any more turn and it would go high mV again
 
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Okay, so back to the beginning....

Are we sure all the output transistors are OK..........Take them all out and measure them.....do not test them in circuit.

Are the output transistors in the correct positions....NPN's and PNP's

Need to test all transistors on the driver boards, starting with the FL driver board......

Need to test all diodes on the driver boards....you will need to lift one leg to do this, you cannot test them in circuit....

Test all fusible resistors, Jim might be able to tell you which ones they are.....
Same here, you will need to remove one leg to test them....

Im not sure whether you have the thermal diode type or the thermal transistor type, but you will need to test these too.........whichever you have....

Write down all the readings and report, if there is something you dont understand let us know......
 
But just for right now.. I cant ell you guys that the markings on the replacement transistors are all "upside down" as compared to the old ones that the markings were right side up.

I have the MJ2193G and MJ2194Gs

By markers I mean the brand and numbers
 
Uh....... crap.. I think I got all 8 polarities mixed up.... I couldve swore i got it right!!

But if I turn them around the screw holes dont match up


Ok I'll post a picture of how they were




Lets just say i got all 8 mixed up.. why arent they blown? At this point Ive tested all 4 on the left heatsink and here they are

(From furthest left)
563
551
538
560
 
Woa.. i can't believe I messed up something so simple... polarity :S

Well, they were all wrong.. this is how I figured it out

I looked at how the old transistors were... for example, the two on the outside, if I connect the positive to the pin that is higher than the other one and negative to the lower one, I get the reading. The two on the inside are backwards from that (lower pin on positive). But, the markings are now all facing right side up.. and they are the right polarity now.

Wow Im shocked I didnt blow up a lot of stuff.. or even the fuses..

Can someone make sure my.. inspection is correct?

Right Heatsink numbers (from left to right)
554
563
546
556

The heatsinks fit without the transistors being screwed in because the holes on them dont match rightsideup. But aren't the screws connected to the receiver? (would this be the collector?) Am i going to have to do some kind of passthrough wire to connect to that or what?
 
The numbers are using the diode testing function. Testing the output transistors.

(If I reverse the positive and negative it shows what means OL in other multimeters)
 
So, do those numbers have a decimal in front of them, like 0.583v? You should read some sort of forward voltage and open (overload) in the opposite direction for B to C and B to E. Is that what the numbers mean? If so, the numbers are not important, what's important is that it read an appropriate forward diode drop and open the other way.

Sorry, I just have a need to understand.

:D
 
Yes that is what I meant, sorry for not being clear.. and I understand your need to understand :D

Now,,, my friend has an idea: desolder the two cables that connect to the pins of the output transistors and switch them around so that the screw holes match without having to do any crazy adjustments. It should work, right?
 
Betomon said:
Yes that is what I meant, sorry for not being clear.. and I understand your need to understand :D

Now,,, my friend has an idea: desolder the two cables that connect to the pins of the output transistors and switch them around so that the screw holes match without having to do any crazy adjustments. It should work, right?
Click to expand...

NO NO NO........do not swap or desolder anything......you are going down a road to disaster here......DO NOT listen to your friend.....

We can help you but you need to stick with Jim and myself and forget what your friend is saying.......

The transistors themselves have polarity a 2SA is a PNP and a 2SC is an NPN......the reason the holes dont line up is because you are only supposed to be able plug the transistors in one way......otherwise the Emitter and Base will be reversed, this is not a polarity issue, its just simply a wrong pinout issue.......thats why they dont fit......

Forget about the stamp on the back of the transistors, the originals were made nearly 30years ago on the other side of the world......the one thing that remains consistent is the pinout of the case style of transistor.....

The MJ21193 is the PNP which goes where the 2SA went
The MJ21194 is the NPN which goes where the 2SC went...

This is what we mean by polarity..........

Do you understand???

If you try and turn those transistors around to and then try and match things up you are going to have a complete disaster on your hands.....

By the way you have used WAY too much thermal paste on those transistors too.....

We want to help, but stay with us, and stop going out on these wild ideas.....there is a lot going on with this amplifier and you need to do exactly what we tell you otherwise we wont get anywhere....

Okay, so summarize where you are at and we will start again.....??
 
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