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Technics SU-V4X problem - no click from relay but indicator lights OK
Technics SU-V4X problem - no click from relay but indicator lights OK
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Old 9th January 2019, 04:54 PM   #21
Briedonis is offline Briedonis
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Originally Posted by SVI2004A View Post
In this amp the manual is incorrect... near on -50 or -43v is no load condition

The -V is fed from a digital transistor UN4211 (Q606) under overload, the SVI will pull up the -V towards ground, which turns on Q606, triggering overload detector feed to IC601
What can cause overload if no load is attached? Short?
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Old 9th January 2019, 05:06 PM   #22
SVI2004A is offline SVI2004A  New Zealand
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Technics SU-V4X problem - no click from relay but indicator lights OK
No overload then... a short is very bad

So 50V you have is fine... if you have too low impedance or short, as Amplifier makes signal, pins 7 and 10 will head toward 0V (maybe you’ll see it dip toward -20V or So)

I recommend not trying to short outputs...these are unobtanium


If amplifier will not come out of protect on power on (safety continuously flashing) check for DC offset
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Last edited by SVI2004A; 9th January 2019 at 05:09 PM.
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Old 9th January 2019, 06:43 PM   #23
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Originally Posted by SVI2004A View Post
No overload then... a short is very bad

So 50V you have is fine... if you have too low impedance or short, as Amplifier makes signal, pins 7 and 10 will head toward 0V (maybe you’ll see it dip toward -20V or So)

I recommend not trying to short outputs...these are unobtanium


If amplifier will not come out of protect on power on (safety continuously flashing) check for DC offset
By accident i shorted main speaker output left directly into right! top stupidity, amplifier was idle, no signal going out at that moment, but amplifier was turned on. after this accident amplifier was still working, until it was switched off, after switching on relay was not working anymore.
just tested IC601, exactly 2.8V on pin 12.
R630 is ~560 ohm
it is 28.6v on relay pin from R630
SV1 2004A is warm now.
Q701, q703, q602, q604 are really hot. q603 is so hot cannot keep the finger on.

both yellow and green lights are nicely on, relay is not. it is quite strange.
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Old 9th January 2019, 07:00 PM   #24
SVI2004A is offline SVI2004A  New Zealand
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Technics SU-V4X problem - no click from relay but indicator lights OK
Check voltage drop over the relay coil should have 24V or so

What voltage is at collector of Q608... should be 0.6v or so

Your amp is ok as its safety light is stable...

Check voltages above... also try gently wriggling/tapping relay to see if it has intermittent/ broken connection to coil
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Old 9th January 2019, 07:58 PM   #25
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Originally Posted by SVI2004A View Post
Check voltage drop over the relay coil should have 24V or so

What voltage is at collector of Q608... should be 0.6v or so

Your amp is ok as its safety light is stable...

Check voltages above... also try gently wriggling/tapping relay to see if it has intermittent/ broken connection to coil
voltage drop over relay coil is 0,1v
at Q608 collector is 0,1v
tried gently and not very gently tapping and wriggling relay, no action.
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Old 9th January 2019, 09:43 PM   #26
4V8s is offline 4V8s  United Kingdom
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Hi, ive just been testing mine also, using the schematics in the service manual ad the advice in this thread.

IC601 pin 12 C04 is 0v at switch on and 2.71v when the safety light goes solid amber. So I guess this is OK (voltage lower than the 2.8v you mentioned SVI2004)

I then measured all three pins of Q608 but I don't know which is which but going off the labels on the circuit board:

E is always 0v
the middle one with the semicircle is always 0v
B is 0v at switch on and 0.66v when safety light goes amber.

So am I right in thinking B looks normal, ie power from IC601, but one of the other pins should then emit a voltage to the coil but isn't?

I havnt removed anything so cant get at the pins for the relay so instead I measured either side of D603 and this was also 0v either side at all times suggesting to me the problem isn't the relay but something to do with Q608 either being faulty, or not enough voltage to switch it on? Where does it take it's power from to send a higher voltage signal to the relay?

(Oh and @ SVI2004, the serial number is FF4J23B221 and the number under the SVI 2004 by the right hand pin when looking from front is 16, if that's what you meant?)
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Old 9th January 2019, 09:49 PM   #27
4V8s is offline 4V8s  United Kingdom
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Oh and also, when I am doing these measurements I don't have any speakers plugged in. Just to check, would there need to be speakers connected in order for the relay to operate? otherwise my tests might not be valid I guess?
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Old 9th January 2019, 09:51 PM   #28
SVI2004A is offline SVI2004A  New Zealand
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Technics SU-V4X problem - no click from relay but indicator lights OK
Sounds like resistor...

One side of resistor should be 50V other side should be 24V or so

Check also that D603 is not shorted
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Old 9th January 2019, 10:14 PM   #29
4V8s is offline 4V8s  United Kingdom
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do you mean R630, the big one? both sides of that are also 0v at all times.

So do I have a rectifier issue? just to double check having no speakers connected would make no difference? im gonna plug one in just in case.....

Anyway, I think it looks like im getting no dc power from the rectifier and also therefore not to the SVI2004 pins that share it, as Ive noticed its not getting warm at all.

tomorrow Im gonna start at the top, with the transformer and impedance switch which looks to select 2 different voltages depending on it's setting. Illl see if that has AC there. then work back from there.

Last edited by 4V8s; 9th January 2019 at 10:32 PM.
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Old 9th January 2019, 10:52 PM   #30
SVI2004A is offline SVI2004A  New Zealand
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Technics SU-V4X problem - no click from relay but indicator lights OK
Yes... 0V at R630, indeed is a feed issue... check for DC at main capacitors. Sounds like you know what you’re lookin for....

4V8s your amp was made on Oct 23rd 1984 1221st V4X produced that day

These tests don’t need speakers... we got to get 50V or 43V (4Ohm setting) to R630
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