Naim NAC62

[Ian Rogers]

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..

 

[Nigel Goodwin]

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]

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]

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]

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]

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:

**broken link removed**

 

[Ian Rogers]

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

 

[KeepItSimpleStupid]

In my experience tantalums have always been VERY unreliable

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.

 

[Nigel Goodwin]

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

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