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Sansui G-5700 "warm up" question


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Hello. I'm wondering if anyone has had similar issues and might be able to help me.

My father has a Sansui G-5700 that has been working just fine for years until a few weeks ago. Suddenly, it seems that the unit needs to "warm up" before it will actually work.

By this I mean, that I can turn on the power and see a display and change the tuner, switch to the tape, etc. but no sound will actually come out. After about 10 minutes, I hear a "click" and the sound turns on. I figured it might be some sort of capacitor that's having trouble building up a charge because if I turn it off, then right back on (before a capacitor might have time to discharge), the sound comes out right away.

Any idea how I might troubleshoot or repair this?

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The G series receivers employed protective circuitry to sense any DC appearing at the speaker terminals. If that condition exists, the relay which controls the output to the speaker terminals will not close, and you will not get any sound. Apparently, after the 10 minute interval, the situation corrects itself and operation is restored (hence the click that you hear shows that the relay is closing). Since both channels are affected, you probably have some electrolytic capacitor issues, although there could be other causes as well. If I recall correctly from having these come through the shop periodically, there's a display on the front panel which says "safe" when the receiver is operating properly and the relay is closed. In any event, this is not something that can be serviced by someone who does not have a great deal of technical expertise. I suggest that you look around for a qualified technician in your area who has experience with vintage solid state equipment (I'm mostly "retired" and now do this stuff only for friends or I'd try to help you out). It's a nice receiver, so if it can be resurrected at modest cost, it's worth doing so.

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You are correct in regard to the "safely operate" LED that illuminates when the relay gets switched on. Both are part of the "sansui f-2980" board within the unit. I may try to look up the schematic and poke around some to see if anything obvious pops out at me. My experience with circuits is more of a class-level than a real life level. So if that doesn't work out, I may try to get an estimate for someone to look at it.

Thank you for the information and for your help. If anything else comes to mind, please let me know.

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this is a very common , and I sell a solution for it. if you are handy with a volt meter, take some DC offset readings. Simply put the meter in the 2 volt range. Measure DC acros the + and - connections of the amp, or if it is easier, you can measure it on the speaker side. be careful not to short out the probe leads to each other. High DC offset will trigger the circuit protection system and it will stay triggered until the internals stabilize, then when the circuit protection system will release, and you hear sound. You will need to take various readings such as at turn on, 10 minutes after, 20 minutes after, etc. Normal reading are usally less than 50 mv. Some class A amps will go as high as 100mv. If you are having circut protection activation issues, your DC offset will come in between 100mv and 300mv. The device I sell is a DC offset regulator. Its inexpensive and will save you big bucks by avoiding having to do a major recap and re-biasing job on your unit. PM/Email me if you want to follow up.

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If the receiver has electrolytic capacitor problems, they need to be replaced if you are to avoid potentially catastrophic failures down the road. It's unwise to rely on fuses, or protective circuitry, to prevent this (i.e. I could have retired 30 years ago if I had a nickel for every device which came in for repair with intact fuses/protective circuitry which didn't do the required job!).

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Tube Fanatic,

Thank you. That version is a much higher quality and is more complete than the vesion that I was able to find.

Here's a link to what I was looking at (http://akdatabase.org/AKview/albums/userpics/10004/Sansui%20G-5700,%20G-6700,%20G-7700%20Service.pdf ) just in case someone is looking at this thread for answers years down the road and the other link is broken.

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