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Technics SU 8080 relay

E

EC1

Super Member
Just acquired a SU 8080, I think I need to replace the relay, it says SSY-21 on the part list of Schematics, where can I get this part? See a couple of listings on fleabay from German, are they the right one, dependable source? And how much of work to replace it? Thanks. The symptom is when turn the unit on the first time, there is a loud popping sound from the speakers and seems the relay is always engaged. There is no a couple of wait seconds for it to engage.
 
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Can you read schematics?

If so, I would look for the voltage across the two coil terminals of the relay, to see if voltage is always present from when the amplifier is turned on.

If it is - it could be that the protect circuit is doing its job. Is there a "protect" indicator on the front of this amplifier?

I would then measure DC offset levels at the amplifier output terminals of the relay.

If your DC offset is OK, then I would look next at a fault with the protect circuit itself. This is usually pretty easy to diagnose - it could just be a capacitor or the relay transisitor
 
Not really, but kind of figure out what you said.
so I just measure from the solder points at the back, they are joint 13 and 14 on schematics.
There is no protection indicator at the front panel. When I turn on the unit, there is this popping sound right away at the speakers. Normally, I think it always will take a couple seconds to hear the relay kick in, but this unit doesn't that makes me think the relay is somehow engaged all the time.
So the DC measurement is done at test posts 412, J10 for left channel and 413, J11 for right channel per Schematics. Will try to post the schematics later.
This is the schematics. So is my understanding correct?
 

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Open this up. It is pretty clean. Measure point 13 n 14, set meter to 200v, it reads -22.9. The DC measurement between 412 n J 10, 413 n J 11, both are at about 0.0, meter set to 200mv. Do these sound right? What is next?
 
EC1 said:
there is a loud popping sound from the speakers and seems the relay is always engaged.
Click to expand...
Possibly the relay contacts have been jumpered. Or contacts welded. Or relay driver transistor is shorted E-C ( TR405 )
 
I'm assuming there is no sound other that the turn on pop.
 
Measure the DC voltage across the speaker binding posts.For both Left and right channel.
 
Are the pre-out/ main-in jumpers in place on the rear panel?
 
It plays nicely. Just the popping noise bothering me and it doesn’t seem right. The back side of the board pic was posted earlier, it looks really clean. The DC offset at the speaker terminals is about 20mv
 
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"Measure point 13 n 14, set meter to 200v, it reads -22.9. The DC measurement between 412 n J 10, 413 n J 11, both are at about 0.0, meter set to 200mv. "

Do these readings make any sense, any advice? Thanks.
 
@avionic, if it was yours, what would you do first? Relay or TR405? sorry to ask this way. I think I might have some spare KSA992, will try that first.
 
EC1 said:
if it was yours, what would you do first?
Click to expand...
I'd test the transistor. First measure the DC voltage at the base of the transistor. There should be zero volts at power up for a second or two, then there should be at least .7 volts.. Unplug the unit and pull the transistor from the circuit board. Then measure the resistance between the collector and emitter leads. Should be in the high megohms or infinite resistance if the transistor is good. If it is shorted. It will read close to zero Ω's resistance.
 
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EC1 said:
If the transistor is bad or shorted, will the unit sing?
Click to expand...
If the transistor is shorted. There will be no delay at power up before the relay "clicks" causing speaker " pops". There should be a couple seconds delay to allow your power supply to stabilize. If the transistor is shorted -- replace it with the A992.
 
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