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Technics SU-3500 fault search

J

John Furlow

New Member
Hi, nice to be on this forum.
A friend of mine asked me to take a look at her Technics amp. I am no electronics whiz but looked for burnmarks on components, bulging capacitors. Everything looks fine. The power on light is lighting but otherwise everything is silent, no hum, no hiss from the speaker. I thought it might be a faulty relay. I read it is supposed not to click.
I appreciate your thoughts
Greetz, John
 
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Hi, thanks for your reply. The links are in place. There is a relay beside the coil isn't there?
 

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Thanks, i checked all the fuses. I could check voltages but where to begin?
What if the relay is faulty. The point is that i thought there should be some sound (hum) coming from a big trafo like this.
 
John Furlow said:
Thanks, i checked all the fuses. I could check voltages but where to begin?
What if the relay is faulty. The point is that i thought there should be some sound (hum) coming from a big trafo like this.
Click to expand...
I've never had a relay fail. It's operating as it should and the amp section is at fault.
Technics units tend to have corrosive glue and overheating caps and resistors.
 
Hi, thanks for the comments.
Measuring 40 Volts on the 2 big capacitors.
The transistors beside trafo are cold.

I read that there is an issue with capacitors on this model ( must be over 40 years old by now) but i don't see any bulging capacitors. Before I have to measure all the components i'd like to have somewhat of an notion where to look
 
John Furlow said:
Hi, thanks for the comments.
Measuring 40 Volts on the 2 big capacitors.
The transistors beside trafo are cold.

I read that there is an issue with capacitors on this model ( must be over 40 years old by now) but i don't see any bulging capacitors. Before I have to measure all the components i'd like to have somewhat of an notion where to look
Click to expand...
Check all power supply output voltages, and an emitter resistor to ground. Report back.
 
The 2 resistors on both preamps measure 9 ohm instead of 47 ohm. Is that normal?
 

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The relay suddenly came to life when i switched on the power, i guess it was stuck since it had been in storage a long time. I guess it's the speaker protection which kicks in?
 
John Furlow said:
Hi, i'm not sure if you meant the AC outputs on the back?
I looked on the parts list but it's not specified which one of the resistors are emitter resistors.
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You should not be working on audio gear if the inference to my comment cannot be made, nor research can be done.
 
inductor said:
thats a rectifier in the picture, the resistors are on the power amp and should be .47ohms
this will take a while ! or better still get it to someone who can repair it
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This is what you wrote
the relay could be o\c but is unusual. see if there are any volts on the 2 big capacitors, and\or are the 2 regulator transistors on the small h\s hot

I have a basic knowledge of electronics, i am interested in the subject and eager to learn new things. Have been a theatre engineer for about 20 years. Do hands on electric repairs. Handle software to control audio, lighting and flybars.
I thought a forum is a way in which people who know stuff share their knowledge with people who are interested in learning stuff.
You could have referred to the service manual which i have on my laptop, so that I could have learned a thing or 2 and i could have done something, i do know how to weld components which in the end will repair this amp, Instead you choose to react arrogant. Clearly this is a forum for snobs, i will be looking elsewhere for info. Thanks for nothing!
 
ivandezande said:
You should not be working on audio gear if the inference to my comment cannot be made, nor research can be done.
Click to expand...

I have a basic knowledge of electronics, i am interested in the subject and eager to learn new things. Have been a theatre engineer for about 20 years. Do hands on electric repairs. Handle software to control audio, lighting and flybars.
I thought a forum is a way in which people who know stuff share their knowledge with people who are interested in learning stuff.
You could have referred to the service manual which i have on my laptop, so that I could have learned a thing or 2 and i could have done something, i do know how to weld components which in the end will repair this amp, Instead you choose to react arrogant. Clearly this is a forum for snobs, i will be looking elsewhere for info. Thanks for nothing!
Je moet gewoon zelf lekker solderen, jij hebt niks te zoeken op een forum
 
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