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Technics SUV-2X safety mode
Technics SUV-2X safety mode
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Old 16th March 2020, 08:42 AM   #1
JMJosse is offline JMJosse  France
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Default Technics SUV-2X safety mode

Hello everybody


A friend of mine given me a old SU-V2X. I've noticed that this amp runs very hot, even on low volume.



It was working fine until the moment it made a clic and enter into safety mode.


I had a look on the net on what could be the root cause and, to stay on the safe side, changed Q501-504.


But no, luck, the problem is somewhere else.


So i did check volatges ou the STK2038 and got strange results


Pin 12 gives 31,4V (supposed to be 1.8), pin 14 : 34.3 (suppesod to be 0) and pin 16, 35.2V (suppsed to be 1.8). All other are according to service manual.


I suppose that the safety feature is detcting this values.
Now, what could be the root cause ? Can you help ?




Any advices are welcome.


JM
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Old 16th March 2020, 09:12 AM   #2
SVI2004A is offline SVI2004A  New Zealand
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Technics SUV-2X safety mode
Letís look at core voltages

Pin 1 (1.8)
Pin 3 (0V)
Pin 5 (-1.8)


Pin 12 (-1.8)
Pin 14 (0V)
Pin 16 (1.8)
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Old 16th March 2020, 09:15 AM   #3
SVI2004A is offline SVI2004A  New Zealand
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Technics SUV-2X safety mode
Sounds like Q502 is short

can try and unsolder Q502 and Q504.... then connect COLLECTOR of Q504 to ground via 6.8K resistor

Check for safety operation.
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Last edited by SVI2004A; 16th March 2020 at 09:22 AM.
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Old 16th March 2020, 11:36 AM   #4
JMJosse is offline JMJosse  France
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Hello SVI2004A


Thanks for the reply.


Q502 and 504 where brand new ones (checked before install).(replaced following your recommendations from another post)



How do I connect Q 504 to ground if its unsoldered form the board ?
(sorry, i'm not a deep expert in electronics, but willing to learn)


I'll do it end of this week, if we are allowed to move (the amp is not where i'm during the week).



many thaks for your help, I'll keep you posted of the outcome as soon as possible.


BR


JM
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Old 16th March 2020, 12:17 PM   #5
SVI2004A is offline SVI2004A  New Zealand
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Technics SUV-2X safety mode
Ahh yes

Solder resistor to collector point (where Q504 would go) this straps -Rchin power IC to ground (stops output stage drifting)

Power ic sounds like itís driven to full output

So with Q502 and 504 removed, and 504 collector terminal connected to ground via 6.8K resistor

Pin 14 should be 0V
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