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SANSUI QSD-2 HUMMMM

maspadaro

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Hello everyone. I bought a Sansui QSD-2 QS-SQ Synthesizer for my system but I am getting a continual Hummm whenever it's turn on, or use it as a passthrough. Now its not a loud humm unless I start increasing the volume. I have opened it up and cleaned switches and pots. that said I still hear a pop whenever I switch the system on or pick 2channel or any other option on the dial
The question I have is : A) is there a grounding for this equipment? B) could it be any other reason for the humm or pop other than the lack of grounding, if so what?

Before I got this, I had a CD-4 demodulator in the same set up and did not have any humming coming from it (the TT was grounded to it).
I will have them both in a chain so I can switch back and forth. No room for a second TT, which is sad since I do have extra turntables.

Any help would be appreciated.

Regards,
Miguel
 

Sonik Wiz

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Hello everyone. I bought a Sansui QSD-2 QS-SQ Synthesizer for my system but I am getting a continual Hummm whenever it's turn on, or use it as a passthrough. Now its not a loud humm unless I start increasing the volume. I have opened it up and cleaned switches and pots. that said I still hear a pop whenever I switch the system on or pick 2channel or any other option on the dial
The question I have is : A) is there a grounding for this equipment? B) could it be any other reason for the humm or pop other than the lack of grounding, if so what?

Before I got this, I had a CD-4 demodulator in the same set up and did not have any humming coming from it (the TT was grounded to it).
I will have them both in a chain so I can switch back and forth. No room for a second TT, which is sad since I do have extra turntables.

Any help would be appreciated.

Regards,
Miguel
Is this a newly purchased unit & it made noise 1st use? Or have you used a while & just started humming?
Grounding, or the lack there of, can sometimes cause problems but it's probably easy for you to experiment & check it out.
If it has the original power supply filter caps on it there's a very good chance those are going bad. IIRC they are pretty easy to access & replace if you are good at desoldering & soldering. If not www.qrxrestore.com seems very highly respected on the forum to send the QSD-2 for repair.
 

DuncanS

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Is this a newly purchased unit & it made noise 1st use? Or have you used a while & just started humming?
Grounding, or the lack there of, can sometimes cause problems but it's probably easy for you to experiment & check it out.
If it has the original power supply filter caps on it there's a very good chance those are going bad. IIRC they are pretty easy to access & replace if you are good at desoldering & soldering. If not www.qrxrestore.com seems very highly respected on the forum to send the QSD-2 for repair.
I agree with Sonik, its often old electrolytic capacitors (they'll have a + terminal and a - one) in the Power Supply that fail, they must be 40+ years old.
 

maspadaro

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Is this a newly purchased unit & it made noise 1st use? Or have you used a while & just started humming?
Grounding, or the lack there of, can sometimes cause problems but it's probably easy for you to experiment & check it out.
If it has the original power supply filter caps on it there's a very good chance those are going bad. IIRC they are pretty easy to access & replace if you are good at desoldering & soldering. If not www.qrxrestore.com seems very highly respected on the forum to send the QSD-2 for repair.
I bought it used . I can do a good job unsoldering\soldering, the issue is knowing which one to replace.
Will contact vintage stereo restoration to see prices. if they are sensible in their prices i will send it in. since this is a synthesizer and not a full blown stereo hope the price are good.

Thank you of the link.

Regards,
Miguel
 

Sonik Wiz

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I bought it used . I can do a good job unsoldering\soldering, the issue is knowing which one to replace.
Will contact vintage stereo restoration to see prices. if they are sensible in their prices i will send it in. since this is a synthesizer and not a full blown stereo hope the price are good.

Thank you of the link.

Regards,
Miguel
I can't find a schematic on hand but notes I made when I worked on a friends QSD-2 say the P.S. Board is F2612. The main filter cap is 1000 mfd 25V & also a smaller cap parallel 10 mfd 25V. Probably just look for the biggest capacitor on the board & the next one to it.

There is a small trimpot on the board used to adjust V+ to 20 volts. The other circuitry is very sensitive to having this adjusted right on. Too low & it functions wonky, & just a bit too high & you'll burn a chip so be careful. Wait perhaps 10 mins to temp stabilize & adjust while actually playing music through the decoder.

There's a lot of people on the forum with vintage gear & that includes me. But most of my stuff I bought new not 40 years later. There's a lot of appeal in vintage gear; some of it looks great & his a true piece of audio history. But honestly if someone asked my advice about what to buy before they spent the money, I would never suggest vintage quad gear anymore unless it had a really good history documentation & refurbished. Otherwise the only game in town is the Involve Surround Master far exceeding the quality of the olden days.

Good Luck!
 

Quadzilla

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Capacitors are the likely culprits, but there are a couple of easy things that you can check. First, try new cables. Then unseat, clean and reseat the multipin bus connector. Mine was a problem when I first got it. I think it was jarred loose in shipping. Next, use a wooden chopstick to poke the solder joints on the input and output jacks while you listen to it, and see if the hum changes or goes away. The solder joints are old too, but very easy to reflow if they need it. Good luck.
 

maspadaro

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I can't find a schematic on hand but notes I made when I worked on a friends QSD-2 say the P.S. Board is F2612. The main filter cap is 1000 mfd 25V & also a smaller cap parallel 10 mfd 25V. Probably just look for the biggest capacitor on the board & the next one to it.

There is a small trimpot on the board used to adjust V+ to 20 volts. The other circuitry is very sensitive to having this adjusted right on. Too low & it functions wonky, & just a bit too high & you'll burn a chip so be careful. Wait perhaps 10 mins to temp stabilize & adjust while actually playing music through the decoder.

There's a lot of people on the forum with vintage gear & that includes me. But most of my stuff I bought new not 40 years later. There's a lot of appeal in vintage gear; some of it looks great & his a true piece of audio history. But honestly if someone asked my advice about what to buy before they spent the money, I would never suggest vintage quad gear anymore unless it had a really good history documentation & refurbished. Otherwise the only game in town is the Involve Surround Master far exceeding the quality of the olden days.

Good Luck!
Thanks Sonik. I am running the QSD-2 on 2 Pioneer Systems SA9500 II (Front) and the 8500 II (Rear). Even though they are from the late 70s they are working great.
My other quad is the pioneer amp preamp qc800 with various quad accessories (8track\RtR\TT\Even DAC\JVC quad EQ). Oh and also the Kenwood quad display 3344 I think. all working well, although cleaning pots and switches is always a must.
I also have various quad pioneer receivers which are working but I believe I will sell them since I won't be using them. No room and I prefer for them to get a home.

Regards,
Miguel
 

maspadaro

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Capacitors are the likely culprits, but there are a couple of easy things that you can check. First, try new cables. Then unseat, clean and reseat the multipin bus connector. Mine was a problem when I first got it. I think it was jarred loose in shipping. Next, use a wooden chopstick to poke the solder joints on the input and output jacks while you listen to it, and see if the hum changes or goes away. The solder joints are old too, but very easy to reflow if they need it. Good luck.
Hmmm I might do that, its easy enough to do in a small equipment. Cables and pots were cleaned and checked but did not check the connections.
Thank you quadzilla
 

par4ken

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I can't find a schematic on hand but notes I made when I worked on a friends QSD-2 say the P.S. Board is F2612. The main filter cap is 1000 mfd 25V & also a smaller cap parallel 10 mfd 25V. Probably just look for the biggest capacitor on the board & the next one to it.

There is a small trimpot on the board used to adjust V+ to 20 volts. The other circuitry is very sensitive to having this adjusted right on. Too low & it functions wonky, & just a bit too high & you'll burn a chip so be careful. Wait perhaps 10 mins to temp stabilize & adjust while actually playing music through the decoder.

There's a lot of people on the forum with vintage gear & that includes me. But most of my stuff I bought new not 40 years later. There's a lot of appeal in vintage gear; some of it looks great & his a true piece of audio history. But honestly if someone asked my advice about what to buy before they spent the money, I would never suggest vintage quad gear anymore unless it had a really good history documentation & refurbished. Otherwise the only game in town is the Involve Surround Master far exceeding the quality of the olden days.

Good Luck!
The voltage should be set to+25V, I recently worked on my QSD-1. I don't see the QSD-2 Manual on HiFi Engine, but I downloaded it from someplace, my copy is a bit hard to read. I would replace the power supply filter capacitor with a higher value, new ones are much smaller than those of the 1970,s.
 

Sonik Wiz

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The voltage should be set to+25V, I recently worked on my QSD-1. I don't see the QSD-2 Manual on HiFi Engine, but I downloaded it from someplace, my copy is a bit hard to read. I would replace the power supply filter capacitor with a higher value, new ones are much smaller than those of the 1970,s.
Thanks for the correction of course you're right. I guess my memory was running 5 V too low.

Also agree that it would be worthwhile, space permitting, to upgrade filter cap to higher value & low ESR/low leakage.
 

maspadaro

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Has anyone ever seen the actual manual of the QSD-2? I know you can "buy" the schematics, which I think its crazy, but if anyone has its please let me know.
Since I will probably won't hear from Vintage stereo restoration till probably monday I will try to see if I can check to make sure nothing is loose first then I will check to see how hard to buy and replace does Caps, any specific brands I should look into?


Regards,
Miguel
 

Circular Vibes

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Just my 2 pennies but if the hum varies in volume with control changes, you don't likely have a power supply issue. Quadzilla suggested tapping around the PC boards and components to hear any difference. He said chopsticks, I prefer the rubber end of a pencil. Both are good. Also check that cables haven't had broken connections at the plugs and that the jacks are reasonably firm fitting both the outside ring and the signal pin. Tapping around switches and pots from the back can be good too. Might be a loose switch contact or a cracked pot element. Might also have a cold solder joint somewhere. You can also make sure all screws are snugged up. PC board screws that double as ground that have loosened or corroded over time can wreak havoc on signal paths Beyond that without schematic or diagnostic skills this is best left for a trusted professional. Keep us informed on your progress please.
 

Sonik Wiz

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Just my 2 pennies but if the hum varies in volume with control changes, you don't likely have a power supply issue. Quadzilla suggested tapping around the PC boards and components to hear any difference. He said chopsticks, I prefer the rubber end of a pencil. Both are good. Also check that cables haven't had broken connections at the plugs and that the jacks are reasonably firm fitting both the outside ring and the signal pin. Tapping around switches and pots from the back can be good too. Might be a loose switch contact or a cracked pot element. Might also have a cold solder joint somewhere. You can also make sure all screws are snugged up. PC board screws that double as ground that have loosened or corroded over time can wreak havoc on signal paths Beyond that without schematic or diagnostic skills this is best left for a trusted professional. Keep us informed on your progress please.
Good point as I remember the level control is actually at the 2 ch input, not 4 ch output where the hummm would be level controlled. This is why DIY electronics is easier than repairing. When you start a project you know what you have to work with, works. Repair is so much detective work, a mystery waiting to be solved.

I still think stuff this old needs some parts upgrading, adjustment of the vario-matrix pots, & off course there are the blend resistors that are best left out.
 

Circular Vibes

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I forgot to mention putting a piece of tape over the metal band om the pencil. I hope no one gets a new hairdo from my OOPS. This is especially true if you are tapping and prodding tight areas. Sonik Wiz, I agree on upgrading some parts as necessary over time. I prefer to troubleshoot and repair first then I am not masking a problem. Mods can be done after too as then you can compare the differences in a working system. Power supply caps in an amp or receiver can fail quickly without warning and take out unobtainium output devices but in decoders and preamps it's more about improved sonics and reliability. I had a Telefunken system taken from 20+ years in storage. It rocked for 15 minutes and then a major cascading fail. Thankfully not so much an Epic Fail as I want to get this system going again.
 
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