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Quad Sansui problem; help???

Trnsfmr said:
The offset pots get set in the middle, or alternatively, if you haven't replaced them, just leave them exactly where they were, as the new settings, once you get it working, will be very close to the old.

Yes, you could use 4.0 ohm resistors. That's well within tolerance. Make sure they are at least 3 watts each. You have to replace these, as it will not power up without them.
Click to expand...

Ok so my teacher has 1.5Ω and then jumps to 10Ω and 15Ω. After that its all in the hundreds or thousands. All the ceramic resistors he has are 10 watts.

So, looks like i'm going to have to buy these arent I :o

And I will leave the offset pots where they are then :)
 
Also, I tested the 2 470Ω 3W power ceramic resistors on the power supply board and they both tested at the 220-235 range with the mult set on 2000Ω

So I'm guessing these are bad too? Maybe I should check the other ceramic resistors next to the tr outputs? :scratch2:

Update: These two appear to be in parallel, so if thats the case then it makes sense if they are 235 because 470/2 is 235. So they are good. Right? :D
 
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The .33ΩK resistors that I was talking about (next to the tr outputs on the power supply board) tested at 02.8Ω with my multimeter set on 200Ω. So those are OK right? Or should I replace those also, since I'm probably going to have to buy the 3.9s
 
Well.. I bought the 3.9s.. and a single cap i was missing a replacement for... now I'll just wait.

I have been meaning to ask about the 53 cold solder joints... when do you guy think I should get around to reflowing them? I see little star-shaped rivets(?) on some of the joints in the quad board.. or maybe thats the selector board? (The one that the smaller quad boards connect into). Underside has lots of connectors.

Obviously it would be wise of me to get it running and then worry about it..... but, it would be good to know whats coming too I think :D
 
Betomon said:
The .33ΩK resistors that I was talking about (next to the tr outputs on the power supply board) tested at 02.8Ω with my multimeter set on 200Ω. So those are OK right? Or should I replace those also, since I'm probably going to have to buy the 3.9s
Click to expand...

Did you make a mistake, here. Did they read 0.28 ohms? If so, that is ok.

"I have been meaning to ask about the 53 cold solder joints... when do you guy think I should get around to reflowing them? I see little star-shaped rivets(?) on some of the joints in the quad board.. or maybe thats the selector board? (The one that the smaller quad boards connect into). Underside has lots of connectors."

Those cold solder joints do not just get "reflowed" If that's all you do, it will usually make the situation worse, not better. What has to be done is this.
1. remove all solder from the pass through joints.
2. scrape the solder mask off, for 1/4" or so, on the trace going to the joint, on both sides of the board.
3. flow some solder onto the scraped back traces.
4. insert a piece of wire, or a cut lead from a cap through the hole and solder it to the traces on one side of the board.
5. go to the other side and solder the wire to the trace on that side.

You are essentially connecting one side of the board to the other with a piece of wire at each pass through joint.

You can see pictures of it at my website http://www.qrxrestore.com/recap-and-restore/
 
One thing to remember is that you cannot get an accurate reading of a resistor as low as 0.33 ohm on a digital multimeter......it will probably read something like 0.8 ohms...........
 
Well I rechecked and it was either 2.8 or 3.0 which... I dont know but they all read the same. I doubt they are bad, but I dont know.. The 3.9s are coming in about next week I think.

Now, I do feel like I have to ask about the dim light tester. So, how exactly am I going to put the light bulb in series with the receiver? I dont want to do something stupid :D
 
:D Nice lurking, and that diagram sure helped.. thanks :)

So I made the tester today in school and put it in a nice little box... minus the switch. I plan to use a power brick to switch it on and off.. To test it I plugged a fan in to the outlet connected in series with a lightbulb. When I turned the fan on the light came on but the fan did not turn. This means that when I will switch my sansui on, it will not power on but instead just light up the bulb if it works? So pretty much as if I'm completing the circuit to allow the lightbulb to light?
 
Betomon said:
:D Nice lurking, and that diagram sure helped.. thanks :)

So I made the tester today in school and put it in a nice little box... minus the switch. I plan to use a power brick to switch it on and off.. To test it I plugged a fan in to the outlet connected in series with a lightbulb. When I turned the fan on the light came on but the fan did not turn. This means that when I will switch my sansui on, it will not power on but instead just light up the bulb if it works? So pretty much as if I'm completing the circuit to allow the lightbulb to light?
Click to expand...

Not quite.......
A fan was probably not the best test for the dim bulb tester.
What will happen is when the amplifier is OK and working properly, the light bulb will maybe glow a little bit, very dim.
If you run some signal into the amp and run it into a dummy load, the amplifier will draw more current, and the light bulb will glow brighter as you draw more current.......
If you have a "Short Circuit" in you amplifier the light bulb will glow at maximum brightness immediately when you turn it on......this is bad and you would then turn it off immediately........
What is happening, is instead of blowing up your transistors and other components, the light bulb will take the energy to light the bulb and the current will just pass through your amplifier.......

In your case with a possible high risk situation, I would use a 100WATT bulb....
Because of the voltage drop with the bulb in circuit, if the amp has a protection circuit, it may not be enough voltage to activate it into operation.... thats another thing to watch out for........

So, very dim or no glowing of bulb = Good
Bright bulb = Short circuit, shut it off immediately......
 
Hi Kev,
I think, because of the 40,000uf capacitor bank, the 9001 is going to want to pull a lot of current to begin with. that should be ok, though, as it is already designed to work in lowered voltage mode until the caps get charged. Then the relay closes and full power goes to the 9001, but by then, unless there is a problem, it should draw little current. So, there might be an intitial bright pulse, as the caps charge, then it should settle down.

Don't forget to remove the quad boards, the cd4 board, and the dolby board before doing this, as they all have IC's, that could be damaged by the low voltage.

EXCITING
 
Great job Betomon..........I will follow your example and build a DBT. I feared using a DBT on the 9001 because of the 'touchy' IC's.

Please post pic's of the DBT and some 'work-pic's'.......
:lurk::lurk::lurk:
 
Trnsfmr said:
Hi Kev,
I think, because of the 40,000uf capacitor bank, the 9001 is going to want to pull a lot of current to begin with. that should be ok, though, as it is already designed to work in lowered voltage mode until the caps get charged. Then the relay closes and full power goes to the 9001, but by then, unless there is a problem, it should draw little current. So, there might be an intitial bright pulse, as the caps charge, then it should settle down.

Don't forget to remove the quad boards, the cd4 board, and the dolby board before doing this, as they all have IC's, that could be damaged by the low voltage.

EXCITING
Click to expand...

Yes indeed, when you power them up on the light bulb they do initially glow bright but then fade down again, yes I forgot to mention that........
That is one of the reasons I like to use a variac......
 
Ok guys thanks for the added info. So what could I use to test my dbt with? Perhaps one of my working receivers? I will post a pic of it tomorrow.. I'm close to dead tired right now :D
 
Ok guys I received the resistors today and just soldered them in. I had some trouble because the leads were getting loose (as in other parts of the power supply board). But I did what I could and to keep the problematic ones down I used a small dab of silicone to secure it to the board (the lead).


I used the tester with my technics first and it worked as you guys described.

Now I should be ready to make the big test....... if I get the confidence :smoke:


Here are the pics of the tester






 
Ok so.. "balls to the walls" right?




First attempt: I flip the switch after.... I must admit... a prayer or two, and nothing.

I look.. and no fuse in the back, duh I was in the middle of replacing it :)

Second attempt: I flip the switch and light comes on but I panic and turn it off... I notice it dimmed slightly

Third attempt: I flip the switch and let the light dim down and..






ACTION!!!!

IT LIT UP!!!!!!


AAAAAAHHHH!!!!! :banana::banana::banana::banana::banana::banana::banana::banana::banana::banana::banana::banana::banana::banana:


The lights in the front panel lit up, and I heard the relay click! But the bulb was still dim and I didnt leave it on for long (max 5 secs).



Now should I put all the boards back in place?!


IM SO EXCITED !!!!!!!!!!!!!!!!!!!! I hadn't seen those pretty lights in way too long :')


:tresbon:
 
Ok so I put everything back on.. minus the cardboard...... which... apparently was a mistake, because when I flipped the switch everything came on again but this time there were little crackling noises, almost like light welding :S So I put the cardboard on and then tried again.. no crackling this time.

Now I have a little test speaker (some cheap tiny thing that came out of computer speakers) hooked up to it. I didnt get anything through it.

So I tried the front headphones... nothing, but rear headphones i got sound. It was very scratchy and noisy.. kind of popping a little if I turned it up.. and I'd say quiet too. All VUs showed movement (albeit not all the same) when music was playing through it.. except for the front left (again.. like at the beginning).

No fuses blown. Oh and also.. i noticed that when I had the front headphone plugged in.. after a little while I saw a tiny trail of smoke coming from where the headphone connects (inside the unit).

So.. whats all this stuff mean? :S
 
Betomon said:
Ok so I put everything back on.. minus the cardboard...... which... apparently was a mistake, because when I flipped the switch everything came on again but this time there were little crackling noises, almost like light welding :S So I put the cardboard on and then tried again.. no crackling this time.

Now I have a little test speaker (some cheap tiny thing that came out of computer speakers) hooked up to it. I didnt get anything through it.

So I tried the front headphones... nothing, but rear headphones i got sound. It was very scratchy and noisy.. kind of popping a little if I turned it up.. and I'd say quiet too. All VUs showed movement (albeit not all the same) when music was playing through it.. except for the front left (again.. like at the beginning).

No fuses blown. Oh and also.. i noticed that when I had the front headphone plugged in.. after a little while I saw a tiny trail of smoke coming from where the headphone connects (inside the unit).

So.. whats all this stuff mean? :S
Click to expand...

First of all, I don't get it and can't figure what the cardboard is. :scratch2:

Ok, well, it certainly seems like progress. at least the fuse is not blowing. I think Kevin had some things he wanted you to do when you powered up. The reason you have no speaker output is because the unit is going into protection and is never turning the relay on to hook up to the speakers.

Using the headphone to listen is the right thing. What you do next is turn it on again, with a 1/4" stereo phone plug into the front jack, measure the voltage on the the left and right. then put it in the rear jack and measure the voltage there. Reach back and feel the heatsinks before you turn it off. If one of them is getting warm feel around til you can tell if it's from the right or left part of that heat sink. Then turn it off.

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.

Report back on your measurements, etc. And we'll go from there. And I'll check in several times tomorrow, so that I can give you some advice earlier in the day.
 
Betomon said:
Ok so I put everything back on.. minus the cardboard...... which... apparently was a mistake, because when I flipped the switch everything came on again but this time there were little crackling noises, almost like light welding :S So I put the cardboard on and then tried again.. no crackling this time.

Now I have a little test speaker (some cheap tiny thing that came out of computer speakers) hooked up to it. I didnt get anything through it.

So I tried the front headphones... nothing, but rear headphones i got sound. It was very scratchy and noisy.. kind of popping a little if I turned it up.. and I'd say quiet too. All VUs showed movement (albeit not all the same) when music was playing through it.. except for the front left (again.. like at the beginning).

No fuses blown. Oh and also.. i noticed that when I had the front headphone plugged in.. after a little while I saw a tiny trail of smoke coming from where the headphone connects (inside the unit).

So.. whats all this stuff mean? :S
Click to expand...

Im at a loss as to what this cardboard is too, Im with Jim on this one....you will have to explain what you mean.......

Now, bad idea to just fire it up and plug some signal into it and listen for some sound.....
You have replaced transistors and other components....you cant just turn it on and hope for the best....
What you need to do it fire it up, and if it all appears to be working with no fires and smoke coming out of it and crackling welding type noises, the FIRST thing to do is go immediately to the bias to check and adjust........

Measuring the bias is going to tell you a lot about the condition of the output transistors and driver section.....
If you have bias current flowing in the range it is supposed to be, you are in good shape.......
No bias current, too much and unable to adjust it down, not enough and unable to adjust it up is going to tell you to start looking into various things.....
You need to make these measurements and report back.......

Next you need to measure the DC offset, now you will have to do this as Jim said with the headphone socket, because the amp will be in protect mode and the relay will have disengaged the speaker outputs.....
I would imagine there is a lot of DC on some of the outputs, you need to find out which ones and how much, and report back..

Once we see what is going on we will know what we are dealing with........
 
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 :)
 
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