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Sansui 2000, transistors question

T

tapedeck77

New Member
Sansui 2000, repair questions

Having recently acquired a Sansui 2000 from the local GW, I set about cleaning it up. Lots of static and scratchiness when first tested. Hosed it down with contact cleaner and after several applications it was much better. After listening a little bit, found the sound to be rather flat and hollow, not what I was expecting from this receivers reputation. There is also a small amount of noise even when nothing is playing. After searching the Internet, and multiple threads here, I found the info about the 2sc458 transistors going bad and needing to be replaced. Bought some ksc1845 replacements, downloaded the service manual and set to work.

I found 7 of the transistors. They have been replaced. According to the service manual, there should be 2 of these on the equalizer amp board (f-1037). Looking at the board, no bright orange little square things. Look at the diagram again. Find exactly where they are supposed to be. They are not 2sc458, they are instead 2sc281 so I didn't replace them. Did a little test after replacing and the noise is still there, but to my ears the sound is better, more detail and depth but that could just be wishful thinking. Which brings me to my questions.

Is the manual incorrect? Did someone just goof and put the wrong part in? Was this maybe one of those undocumented design change things?

Should I go ahead and replace these two transistors with the new ksc1845s?

I'm wondering if the low noise issue is maybe not related to the transistors and I need to look elsewhere, perhaps replacing capacitors?
 
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Sansui used both the 2sc281 and the 2sc458 in the 2000. Neither are good for long term noise reduction. Go ahead and replace them. And yes Sansui made all kinds of undocumented changes, IMO more so than any other manufacturer.

IIRC, Without digging out the scat, You should have 2 458's on the main amp boards total, 4 to 6 on the tone control board and 2 on the eq amp (or in your case 2sc281's).

If it's sounding bleh, and flat after replacing the transistors, a recap of the electrolytics will go a long way to rectifying that. After all it is 44-46 years old. Those elna's are pretty dry by now.

Larry
 
Cool, thanks for the info. I will go ahead and replace those two transistors and see if that makes a difference. I have a feeling a recap is in my future, which is not necessarily a bad thing. Gives me an excuse to spend some quality time alone with solder fumes and my thoughts.
 
Well, that didn't go so well. I replaced the two transistors with some difficulty, the back of the board was covered with some sticky substance which made getting the solder to flow difficult. Cleaned it with some alcohol, managed to get a decent solder connection and tested the sound. Very low volume with lots of static. Tested with speakers and headphones and multiple inputs. Same on all.

Since I was planning on recapping anyway, I set it aside while I ordered some parts. I went ahead and ordered two new transistors thinking maybe the KSC1845 were bad or not a good substitute for the 2SC281. I found a website that suggested a few substitutes and I went with a BC549C. I also order a bunch of caps.

Once the parts were in, I replaced the two transistors and all the caps on this board (f-1037) except for the two tantalum caps that I had trouble finding a replacement for. Took some time to try to make sure all the solder connections on the board were good. Put the board back in place and hooked all 21 wires back up. Tested with headphones. Same problem as before, very low volume and lots of static.

At this point I am kinda stumped as to how to procede. Any advice would be appreciated even if said advice is to toss my soldering iron in the trash and not make it any worse than it already is.
 
Sounds almost like you mis installed a couple of the transistors. The leg basing on the new ones IS NOT the same as the old ones. Which is why there are Data sheets you can download and they show the leg basing.

The sticky stuff is old flux or release film from the factory. Acetone will take it off easily.

The 1.5uf tantalums can be replaced with 2.2uf 50V ECQ stacked film caps (Panasonic). The tantalums have a bad hx of not working well in audio paths.

Get the Data sheets for all the transistors you replaced and double check the basing. Basing is from the front (writing on the front) and the legs DOWN, starting LEFT TO RIGHT. You may have to do some fancy bending on a couple to get them in the right holes but it can be done.

The KSC1845's are the preferred replacements for the 2sc458 (and the 281 that replaced it) since the 2sc2240 is now obsolete. The BC549 is ok too. In any event check the leg basing on all of them, then double check the capacitor polarity. You might have one or two in backwards.
 
I put this aside for a little while because it was frustrating me and I had other non-electronics projects to work on. I pulled it back out on Monday to work on it some more.

Replaced the tantalum caps with film and replaced the transistors again with new ksc1845 thinking perhaps I had fried the previous ones from too much solder heat. Still the same issues. I am pretty sure I have them in correctly. I looked up the pinout before doing the other transistors and they all worked fine after replacing. It was only after replacing the transistors on the equalizer board that I had any problems. I matched the legs to the labels on the board. I can try to get some photos so someone with more knowledge can see if they are installed correctly.

My theory at this point is that trying to desolder with all that crap on the board caused me to put too much heat into it and damage one or more of the traces and that's causing a bad connection. Does this sound reasonable and if so, what can I do?

Like I said, I'm thinking maybe I got myself in too deep. :sigh:
 
I've found the markings on the 2000, 2000A, and 2000X to be accurate on the Eq board and Tone control boards, actually all the boards. And I double check the pinouts of the old and new parts.

Let me open my 2000 and take a pic of the EQ board. Might be a day or so.

Also you don't need to remove the leads from the board to gain access to the underside. It's a bit tight but it can be rotated at least 90*. This may be your problem more than the transistors (removing and replacing all the wires.)
 
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Ok. I just opened up my 2000. I apparently did not replace the transistors but someone else did. 2sc945(2sc458) and BC 501(2sc650).

With the 1845 (ECB PINOUT LEFT TO RIGHT) all of the transistors will be facing approx the same way (toward the end with the Tantalums). The arrows on the drawing is how the face with the lettering is oriented. With a Center Collector PINOUT
bend the center pin back a little, then spread the E & B slightly to go in the holes.

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The other thing I would do is to trace out the wiring from the board to the other end on each individual wire, and correct any miswired leads.
 

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Thank you Larry for your help. I think I have transistors in correctly, but I will double check when I get a chance and also try and check the wiring and make sure it's all hooked up correctly.
 
I finally pulled this out and started working on it again a few weeks ago. I had ordered a replacement EQ board off eBay to test if I had messed up the old board. I had the same problem after installing the replacement board so I gave up on it for awhile. After pulling it back out and checking it, everything seemed to be working fine. Apparently sitting on a shelf for a couple of months fixed things.

I proceeded to finish my recap except for one cap on the ripple board that was a higher value than I was expecting. Got the rest of electrolytics replaced and the one higher valued cap has been ordered and will be replaced next time I work on it. All the 2sc458s have been replaced with ksc1845s. Sounds pretty good at this point but there is still a bit of noise with volume off, enough that's it is kinda annoying.

I know it has been stated in other threads that the 2000 should be pretty quiet if things are working properly so I was hoping the experts here could weigh in with things to check/replace in order to potentially lower the noise floor some more. All I have in the way of test equipment is a basic multimeter. I was wondering about the carbon comp resistors or some of the other transistors maybe being the culprit. Thoughts?
 
assuming the vol pot is grounding the signal when its turned right down the problem is further on .
if the unit has pre main connectors pull them and see if noise changes .if so insert shorting plugs into main in and see if any change .. if no pre main insert shorting plugs into an input such as aux and note the difference if any .
 
I would have thought if you had "noise" it would be caused by either a transistor or cap. Is this "noise" in both, or only one channel? As petehall states, check your volume pot too. Not familiar with this model - but also as Petehall states - if you can "seperate" the pre and power stages with jumpers at the back, do this to identify what stage of the amp is causing the issue. If you had issues with the soldering, you may also have a poor solder joint - you may need to reflow the work you have already done. what type of noise is it? can you describe it?
 
This model doesn't have the preout and main jumpers unfortunately, so I can't check it that way. I will try to find some shorting plugs and check it with them installed.

The issues with soldering where on the old EQ board which was a different type of board than the others for some reason and had lots of flux and crap on the backside. The rest of the boards were a lot easier. I have checked the joints on the stuff I did and there are no obvious problems, which doesn't necessarily mean they are all good. I will double check them.

The "noise" is a low hiss, what I would call white noise.
 
What speakers are you using with it? High efficiency speakers (>95db/1m/1w) will show up any or all noise in the unit more than a medium or low efficiency speaker.

When I connect mine to my SP-2500's (96-98db) I get some "white noise" with the volume all the way up on AUX with shorting plugs. But I'm less than a foot away from the speaker to hear it. on any other speaker I have (ADVENT NLA or Bozak 203's, KLH-20's) I can't hear it. So it may be speaker dependent.

Sansui apparently used a flux/solder/solder mask that had some impurities in it during the 2000-2000A-2000X era. Wave soldering didn't help with the boards either. Some have too much and some too little solder. The Brown boards are especially susceptible to bubbling solder and air pockets IMO and experience. Try and remove as much of the solder as possible with solder wick and resolder with good quality 60/40 or 63/37 tin/lead rosin core solder. DO NOT USE Lead-Free rosin core or plumbing(acid core) solder.

Larry
 
My speakers are Polk Monitor 60 series 2. They are rated at 90db sensitivity. The noise is noticeable several feet away, it's not loud but it seems louder than it should be if everything was good.

It may be a few days before I can spend some time working on it, but when I do I will check all the solder joints and redo any that seem suspect.
 
I had a chance to work on this a little bit over the weekend. I checked solder joints, redid a few that didn't look great. The two boards off the back of the faceplate that hold the push button switches had a lot of bad joints so I did my best to redo the joints on them. Tested with headphones and the noise was still there, hard to tell if it was better or not. Put the covers back on and carried it to the bedroom to hookup to the speakers for more testing. The old problem of very low staticy volume was back. Sigh.

Apparently the process of putting the covers on and moving it somehow brought the problem back. I took it back to my work area and fiddled with it. Worked all the switches until I got to the speaker selector. When changing speaker outputs, I would get a pop and then the volume came back. Switching back and forth would cause a pop and then it would randomly come and go. I let it sit and the next day went to work on it some more. Everything was working. Flipping the speaker selector, no pops and it didn't cut out.

Now I'm wondering if the problems are related, if there is something loose that is causing both. The problems are in both channels, so that indicates to me it has to be somewhere that would affect both channels. Beyond that, I'm stumped. Any suggestions on things to check are appreciated.
 
Get some DeOxit D-5 and go thru ALL switches, and pots VIGOROUSLY! Multiple applications are sometimes necessary on these older units. Follow up The DeOxit (D-5) with either Faderlube (F-5) or DeOxit Gold (G-5). Both will replenish the lubricants that D-5 washes out.
 
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