Technics SA-5760

[Gary88]

I have a Technics SA-5760 that I bought new in 1977. It has served me well all these years but a few years ago I started getting crackling/hissing and popping out of one channel. I installed a fuse inline to my Klipsch speakers so as not to harm them. This symptom comes and goes and when it does it blows the fuse, (2 amp fast blow). When it happens, I turn the volume down all the way and you can still hear hissing from the speakers. I must turn it off and back on to get it to stop and then it may do it again right a way or wait two or three songs before doing it again. I have had it in factory repair and other repair shops 4 times and no one can get it to act up in there shop but it does just a few moments after I have it back home. I would love to get this unit fixed, weather I do it or find someone to do it. HOW THE HECK DO WE FIND OUT WHAT IS WRONG when it won't do it in the servicers shop??? I'm not giving up on this. Does anyone know of a good servicer in the Dallas or Oklahoma City areas?

 

[73's de Edd]

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Sir Gary88 . . . . . . .

Which is your problem channel . . .the right one or the left one ?

73's de Edd



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[Gary88]

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Sir Gary88 . . . . . . .

Which is your problem channel . . .the right one or the left one ?

73's de Edd



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Thanks for typing. It starts in the left channel then may stay in it or may bleed into the right. Yesterday it started out by the volume increasing in the left channel before it started going fuzzy, and making its regular noises. I turned it off before it could go full force and blow the fuse. I was playing a cassette tape through tape 1 but it will do it through as far as I know any media, record, real to real, tape, or cd.

 

[Gary88]

Thanks for typing. It starts in the left channel then may stay in it or may bleed into the right. Yesterday it started out by the volume increasing in the left channel before it started going fuzzy, and making its regular noises. I turned it off before it could go full force and blow the fuse. I was playing a cassette tape through tape 1 but it will do it through as far as I know any media, record, real to real, tape, or cd.

Also, I do have the factory service manual and electrical schematics from Panasonic for this unit, the real McCoy's not aftermarket ones.

 

[elebish]

Check the line voltage for overvoltage and noise. May need a scope to do that and will really know how to use it for proper triggering and source.

 

[Gary88]

I have got my hands on a meter. Simpson 260-8 and now I think a signal generator would help. If a signal generator would help which type would I need? Function type or some other? Any thoughts on this would be welcomed.

 

[73's de Edd]

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Sir Gary88 . . . . . . .

You r r r r r e b a a a a a a ck !

Your Simpson should suffice.

Now . . . . . do you read "schematicese" ?

You probably just have a problem with that left channel alone BUT with it secondarily affecting the other channel a mite , due to their shared power supply.
Particularly, considering that your fault is demanding enough to take out a fuse.

Vice a signal generator or function, if a constant monitoring is needed, an audio source can be used.
HOWEVER if a referenced constant level, using po' boy technology, we can use a capacitor for DC isolation and a voltage divider network and a sampling of power supply 120 cycle ripple as an audio signal test source.

Will take me a bit to find that units schematic in my archives again . . . . . . but you can confirm that unit is HEAVEEEE.





73's de Edd




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[Gary88]

Mr. Ed, I do have the factory service manual and schematic so i'm good there. Yes, the problem currently is affecting both channels. I moved the stereo from one room to another last month and now both channels have no sound, just crackling and popping and hissing and at times nothing at all and neither fuse at either speaker has blown this time, but I am keeping the volume knob turned all the way down. When I do turn it up a little nothing changes so I go back down all the way. I am bran new to checking stuff on a circuit board. I have experience checking pins going in and coming out of the board but on the board its new to me but I am going to learn it. I not sure where to start.

 

[Gary88]

Hello Mr. Ed, I have the factory service manual and the factory schematics so i'm good there. I moved the stereo from one room to another last month and now I have both channels doing the same thing. No sound, crackling, hissing, and popping in both with the volume knob turned down all the way or turned up a little. And it comes and goes but no sound at any time from the music. I don't know where to start. I am experienced at checking connections going in and coming out of circuit boards but no real experience at checking components on the board. I think the music works fine out of the head phones but I'll need to check again before I say more on that.
Thanks for any help.

 

[elebish]

Hello Mr. Ed, I have the factory service manual and the factory schematics so i'm good there. I moved the stereo from one room to another last month and now I have both channels doing the same thing. No sound, crackling, hissing, and popping in both with the volume knob turned down all the way or turned up a little. And it comes and goes but no sound at any time from the music. I don't know where to start. I am experienced at checking connections going in and coming out of circuit boards but no real experience at checking components on the board. I think the music works fine out of the head phones but I'll need to check again before I say more on that.
Thanks for any help.

You will probably have to troubleshoot the power supply as this is the most common problem that will affect both channels with the same noises. Clean the volume control if you have a dusty environment. Next, the main filter electrolytic capacitors should be disconnected and temporarily substituted with similar value caps. There will be one for the Negative and one for the positive voltages that feed the main output transistors and could feed the drivers also. Look for neg and pos 35 to 60 volts dc. Observe polarity of meter leads when checking voltages with the 260. The largest capacitors will be the ones to check, Be careful, these store voltages that can zap a person. Bleed the caps with a 1k ohm resistor at 2 to 5 watts. A scope is always the best way to troubleshoot a system but requires knowhow. I highly recommend someone with experience to help you.
Note: You won't be able to test those caps effectively with the 260. That is why I suggest to substitute them. I can't tell if the caps might be temporarily shorting or opening because both can cause your problem. Also check the solder joints at the capacitor leads on the circuit board and wiggle some of the components with a wooden stick to see if you can duplicate your problem.
Good luck.