Help setting quiescent current nap 135

[Milspec1]

I just finished recapping my pair of CB 135's following this thread. https://pinkfishmedia.net/forum/threads/naim-nap-135-servicing-thread.165333/
Big thank you to Colasblue. Very helpful thread. In it he describes the way to set quiescent current. When connecting it to the resistors as shown I get about .9mv and am unable to make any adjustments that move the value . Measuring across the resistors picture below measures 15 mv and am able adjust down to 7mv. i am doing something wrong ?

https://imgur.com/UsezTcS

https://imgur.com/7SG8q7V

 

[Richard Lines]

@Milspec1 - Do you have speakers connected??

Regards

Richard

 

[Milspec1]

Yes. I did. Should it not have a load connected? The 2nd time I tried I removed the XLR cable . Although nothing had been playing.

 

[colasblue]

Older boards don't have the same layout so don't simply follow where I physically connected the meter probes visually, actually trace the circuit and connect across the two emitter resistors.

Your board layout looks the same as the one in post 31 here so the second picture seems to have the correct test points.

NAP140 Bias Problem

Murray - yes, you want to see at least 4.5mV across any ONE emitter resistor (ie at least 9mV end-to-end). Up to double that does no harm, but any more brings no benefit in terms of lower distortion, and wastes a little more energy in idle disspation. Going far beyond that point risks...

pinkfishmedia.net

There should be no signal or load connected when making the measurement.

 

[martin clark]

I think your 0.9mV is spurious , because you are measuring that across the in-series output resistor (also 0R22 value). For which you should read 0v! (excpet DVMS have such a very, very high input impedance, seeing something like a fraction of a single mV is just error, esp with economical DVMs)

Set for 7- 8mV in the way you can, and try that. Looks good to me.

 

[Milspec1]

Ok. So the first picture is right ? it is the only way I could get it to set. I found location on another thread of someone setting there cb 25o but could not find it again to go back and read it. Checking my search history seems that I have spent more time on this site than I had thought.lol

 

[James Evans]

Don’t do this with speakers connected. If you slip with a probe and accidentally fry an amp board it can take the speaker out with it.

 

[Milspec1]

i just seen this

Older boards don't have the same layout so don't simply follow where I physically connected the meter probes visually, actually trace the circuit and connect across the two emitter resistors.

Your board layout looks the same as the one in post 31 here so the second picture seems to have the correct test points.

NAP140 Bias Problem

Murray - yes, you want to see at least 4.5mV across any ONE emitter resistor (ie at least 9mV end-to-end). Up to double that does no harm, but any more brings no benefit in terms of lower distortion, and wastes a little more energy in idle disspation. Going far beyond that point risks...

pinkfishmedia.net

There should be no signal or load connected when making the measurement.

thanks you sir.