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Quad Sansui problem; help???

What is a totally good idea, is to not take things off the circuit boards until you are ready to replace the parts.
This way you will not forget where and what way they go, sometimes the markings on the circuit boards can be wrong, and sometimes the schematics are wrong too.
This is because during the production run, things are upgraded and changed along the way, and they dont always release service updates for the schematics and circuit boards.
So as a habit, I dont take anything off unless I am ready to fit the new part or take the part off the board to test it.
When I do take something off, I take a picture or I draw my own diagram to make double sure it goes back in the right place and the right way round.
This applies to Capacitors, transistors and diodes.....

What would be the first thing to do now, is test the output transistors.

Do you have a diode testing function on your multimeter?
This is by far the easiest testing function to give a definitive diagnoses on your transistors...
Do you know how to test transistors?
Do you know the pin out for the T0-3 type transistors?

What we will do is we will take one out, test it and then if it is good, put it back in. Make sure you have thermal paste, and when you apply it, dont put too much on, there will also be a mica washer, which insulates the body of the transistor from the heatsink, this is because there is the full DC rail voltage on it and the heatsink is obviously earthed because it is bolted to the chassis.
So, no mica washer........it goes BOOM!! No thermal paste.....it gets too hot and then goes BOOM!!

I can guide you to the way to test the transistors if you need me to.
When you test them report the findings....like Ive shown below.
For example B>E = .450, B>C= .450, C>E= OL like that.....then we know exactly whats going on.
 
Alright guys, I tested a transistor and got 570 or close to that. Should I test all of them to make sure? I am SO glad to know that its not blown.

I will start taking things off when I get the parts then. Ill make sure to take pictures as I go and label stuff. Today my dad and I are ordering the parts. But before I do, I wanted to ask about the two little (diodes or resistors not sure what they are) between the 4 big black caps, do they need replaced? I used the diode testing function and got .04 on both of them, both ways.
 
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The 3.9KΩ resistors, what kind are they? I can't find them on metal film resistors. And also, are the metal film resistors through hole? or what type?
 
Betomon said:
Alright guys, I tested a transistor and got 570 or close to that. Should I test all of them to make sure? I am SO glad to know that its not blown.

I will start taking things off when I get the parts then. Ill make sure to take pictures as I go and label stuff. Today my dad and I are ordering the parts. But before I do, I wanted to ask about the two little (diodes or resistors not sure what they are) between the 4 big black caps, do they need replaced? I used the diode testing function and got .04 on both of them, both ways.
Click to expand...

Okay so you are using the diode testing function yes?
You are measuring forward voltages here and what you need to do is make sure if it reads 570 one way, then reverse the polarity, the red and black leads on the multi meter and do the same test, and it should NOT pass any voltage. Should read OL.

By all means test all the output transistors.....

Im not sure what you are referring to between the caps, if they are diodes, you need to desolder one end and lift one end out of circuit because the surrounding components will interfere with the readings.......

Take pictures and show us what your looking at.......
 
Betomon said:
The 3.9KΩ resistors, what kind are they? I can't find them on metal film resistors. And also, are the metal film resistors through hole? or what type?
And the 8 4.7@80v nonpolarized, somtimes called BP, I only found 3 different ones, one kind in stock.
Click to expand...

The 3.9R resistors are ceramic, usually called power resistors. the metal films are through hole. And about the BiPolar caps, yeah, there are usually not a lot to choose from.

Sounds like you're doing great. A big part of this whole thing is learning how to buy parts. It's really cheap if you can buy from a company like Mouser. The buyer interface is daunting at first, but you will learn to love it. Remember if you're not sure about a part, click on the datasheet and there will be a picture there. It should look like the part you're going to replace, maybe smaller, but similar.

If I could suggest, it sounds like maybe your are using the transistor check function on your multimeter, where you plug it into the BCE holes? Is that what you're doing? I think what Kevin is describing and wants you to do is to use the diode function on your meter and test that way. If you are unsure about this, google "how to check transistors" or similar. You check B to E, B to C, and then turn the leads around and do it again. This is really important to learn how to do it, and get it right.
 
Yes it does have a diode testing function. And yes the opposite way read 1, which is the same as OL in another multimeter im guessing because when I touch both ends it read that.

Here is what I was talking about earlier

 
No I am not plugging it into the B C E holes. I just use the two wires connected to VΩmA and COM. The function symbol is like a little arrow with a vertical line at one end. That is the same thing that measures continuity right?
 
Also, I'm having trouble finding the 3.9 resistors. I go to passive components > Resistors > Ceramic Composition Resistors

I am a little bit confused; on the resistor itself it says 3.9ΩK, so on the website does that mean 3.9 KOhms? If so, there are only 1 and 2 watts. For the 3.9 Ohms, there are 1, 2, 3.5, 4.5 and 5.5 watts. But these dont look like the one in my sansui. Am I looking in the wrong place? :S
 
Betomon said:
Yes it does have a diode testing function. And yes the opposite way read 1, which is the same as OL in another multimeter im guessing because when I touch both ends it read that.

Here is what I was talking about earlier

Click to expand...

Okay wait a second.......If you are touching the two probes together it reads 1?? Is that right......
What that means if I am understanding you correctly, is 1 will indicate a short circuit. (its actually probably 0.001)
OL is generally what a meter will read when it is reading OPEN CIRCUIT or NO CONTINUITY.......
When you are not touching the leads together does it read OL??

Let me know before we go any further, it is really important you get this right otherwise blown components might go back in and we think they are okay, this will cause big problems when we are trying to diagnose....

What you have there is a 10K 3watt resistor across the capacitor.......
 
Sorry, this is what I meant. When the probes are not touching, it reads 1 all the way to the left of the screen. When they touch it reads 002.
 
Betomon said:
Sorry, this is what I meant. When the probes are not touching, it reads 1 all the way to the left of the screen. When they touch it reads 002.
Click to expand...

Okay good, carry on measuring those output transistors........
Remember there are NPN and PNP polarity transistors, so when an NPN reads 570 one way, the opposite polarity transistor will give and open circuit result with the same test..........
 
Maybe pictures will explain better.

This shows the measurement one way, and then the other. Then it shows what the multimeter reads when the prongs are touching. Hopefully this explains things better :D





 
kevzep said:
Okay good, carry on measuring those output transistors........
Remember there are NPN and PNP polarity transistors, so when an NPN reads 570 one way, the opposite polarity transistor will give and open circuit result with the same test..........
Click to expand...


Ok cool, I'll keep testing :)
 
First 4 passed with flying colors on the right heatsink. All over 550 and under 580.

UPDATE: Next 4 did as well. :)
 
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:tears:You no before this is said an done there is going to be :dammit:times:scratch2:thinking times:dunno:da times:O and yes:withstpd:times But at the end when everything come's together there will be:thmbsp::banana::beer::rockon::yippy:TIMES
Good luck and best wishes
Joe
 
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Okay, one thing you could think about investing in, if you like to do this sort of work and you think you will do more, is a good multimeter.......

For me there is one make of multimeter.....FLUKE.....good thanks....

I have this one

img0188j.jpg
 
Betomon said:
Also, I'm having trouble finding the 3.9 resistors. I go to passive components > Resistors > Ceramic Composition Resistors

I am a little bit confused; on the resistor itself it says 3.9ΩK, so on the website does that mean 3.9 KOhms? If so, there are only 1 and 2 watts. For the 3.9 Ohms, there are 1, 2, 3.5, 4.5 and 5.5 watts. But these dont look like the one in my sansui. Am I looking in the wrong place? :S
Click to expand...

OK, that was a hard one to figure out. It is under through hole, wire wound. Here's the part #
280-CR5-3.9-RC

Put that part number in at the top of the page and it should get it for you.

Those resistors are 3.9K, I think, at least on all the 9001's I've seen so far, the one on the bottom of the caps. I actually like to replace them with 10k 1/2 watt.
 
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