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Technics SU-V4X Dead?
Technics SU-V4X Dead?
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Old 8th January 2008, 10:53 PM   #1
bitbandit is offline bitbandit  United Kingdom
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Unhappy Technics SU-V4X Dead?

Hi, I have a Technics SUV-4X that I have had since new in 1984. It has begun intermittently shutting down to safety mode. Sometimes it runs for a few hours, other times a few seconds.

I have replaced Q501-504 but still the same. Also checked over the main board for dry joints. All psu voltages look to be correct and stable as far as I can tell.

Does anyone have any suggestions as to how I can tell if it is the dreaded SVI2004A that is dying?

I'd hate to pension the amp off - I love it and I have yet to find a modern amp that sounds anything like it. Latest audition was Arcam A70 which sounded like the bass rolled off below about 500Hz!

Any suggestions welcome.

Cheers.
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Old 19th August 2008, 02:13 AM   #2
SVI2004A is offline SVI2004A  New Zealand
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Technics SU-V4X Dead?
There is a way to id the fault.

check that pins 3 and 14 are 0V

then check pins 7 and 10 should be near -rail voltage

- i have a V4X of mine doin this to me at the moment, its getting DC offset on both channels (bout 2 - 4V) - hard to trace at the moment but definately toward the front end i suspect an elusive dry joint on the front end earthing strap.
definately not the SVI
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Old 26th August 2008, 04:09 PM   #3
David Everett is offline David Everett  United Kingdom
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Default Technics SU-V4X

Hi, it sounds like I have the same fault with my original SU-V4X as you described in your post and I wondered if your request for suggestions earlier this year provided you with an answer that resolved the problem?

Any help would be much appreciated.

Thanks.
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Old 26th August 2008, 04:09 PM   #4
bitbandit is offline bitbandit  United Kingdom
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Hi, thanks for the reply.

I have a couple of these amps now and I have temporarily left the one that is cutting out to one side as I don;t have much time at the moment. Hopefully soon....

From memory, 3 and 14 are at 0v with a slight rise (80mv and noisy on the scope) to pin 3 when the fault appears. Everything else seems to stay as was when no fault, so possibly a fault further back as you suggest. If I get a chance I'll run it up and let you know what I find.

I have a second one with a slightly distorted left cd input. Only shows up on vocal harmonies, like on the first track of not too late by Norah jones - very selective and specific fault! I switched to the tape input which was fine but 6 months later that now seems to be doing the same. I think it is probably the input switch chip. Nothing to do with the switch to safety though!
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Old 26th August 2008, 05:32 PM   #5
Shaun is offline Shaun  South Africa
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Technics SU-V4X Dead?
I have a SU-V2 that has the problem of cutting out when using a certain input. I also now use TAPE instead of AUX. Seems to be a selector switch problem. The selector switch is a specialised design. Anyone know if a replacement is available?
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Old 11th June 2011, 11:45 PM   #6
hbc is offline hbc  United Kingdom
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For the record, believe I have just fixed one of these, replaced the Vas transistor Q502 with 2SA1208 as it is what I had. Old one seemed to be going open circuit and putting amp into protection. Worse on the hi Z option.
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Old 2nd January 2018, 09:01 AM   #7
ssi is offline ssi  United Kingdom
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I had one channel cutting out from time to time in an SUv4x - especially when cold. Spent ages finding the fault including resoldering lots of joints and replacing the relay. In the end it was a dry joint on the speaker terminal. All good now!

Old thread but may help somebody.
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