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Naim NAC62

Ian Rogers

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Hello. I don't do amps.. But I have a pre amp that has no output

The dual solid state relay ( I think that is what it is ) isn't turning on.. There is a two transistor darlington pair ( both ZTX214 ) just at the bottom of the picture

Injecting a signal it arrives left channel pin 8 and should leave on pin 5 right channel is on pin one and should leave pin 4.. Pin 2 and 7 are 12v and pin 3 and 6 are ground. Injecting 12v on to pin2 and 7 and it runs... As these seem superflous as the relay should work 24/7... why should I replace them.. I could just bypass... Whats the opinion of the group..
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Nigel Goodwin

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Is it actually a solid state relay?, I would imagine it's FAR more likely to be a reed relay - a Naim is a high quality (and expensive) unit, so you don't want anything in the path that will reduce audio quality - and a simple pair of mechanical contacts is as good as it gets, better than any solid state solution. Another option could be an LED and LDR combination?.

I would imagine it's there simply for muting, perhaps to stop any clicks when you switch inputs etc.
 

Ian Rogers

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The fault has been traced to a tantalum on the 24v supply.. short circuit.. Which is funny as its rated at 35v but the input is 40v+ and even I know that's not good.

It is indeed a reed relay.. Once the amp is fixed, I will retry.. But I need to map out this reed circuit as there isn't a voltage on pin 2 and that PNP pair is supposed to supply it..
 

Nigel Goodwin

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The fault has been traced to a tantalum on the 24v supply.. short circuit.. Which is funny as its rated at 35v but the input is 40v+ and even I know that's not good.
In my experience tantalums have always been VERY unreliable - the usual 'excuse' is that you should never exceed even half of the rated voltage - so the rated voltage is obviously completely wrong.
 

Ian Rogers

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One question.. Now I know what it is.. In the datasheet there is a "dotted" flyback diode shown... Now the diode immediately to the left of the large cap goes across the voltage rail.. Is this a recommendation or is it within the reed relay?
 

Nigel Goodwin

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One question.. Now I know what it is.. In the datasheet there is a "dotted" flyback diode shown... Now the diode immediately to the left of the large cap goes across the voltage rail.. Is this a recommendation or is it within the reed relay?
I bought some similar looking reed relays a few months back, and they had an internal diode - so you had to ensure you connected them the right way.

And I've just checked the datasheet for one right near me now, and that apparently has a diode in as well:

 

Ian Rogers

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I put a 65v electrolytic in... I now have a nice stable 24v... I just need to wait for a TO220 insulating kit as it cannot be grounded to the case..

Worst case.. I'll stick a 12v zener in to supply the relay.. The "mute" is a simple switch on the front that just disconnects the input.. I cannot see ANY circuit that connects to the base of the PNP.. other than a potential divider
 

Nigel Goodwin

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That's about right. There was a time frame where they were very unreliable and a lot of Tektronix stuff is affected/ They have apparently gotten better. They are not tolerant of overvoltage.
You mean not tolerant of voltages more than half their rating :D

In fact not even that, the vast number of failures were mostly 25v or 35v tantalums on 12V regulated rails.
 

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