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Looking for Nikko STA-5010 service manual or bias set procedure

P

P. S.

Active Member
Hi,

I am struggling to find the service manual for sta-5010. Seems like there's just one version of sta-5010 schematic only circling on the internet. I already recapped this receiver and quite happy with the sound. Now I need adjustment of the bias and dc offset.
If you have access to this procedure - can you share?

Thanks,
Peter
 
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Thank you. I will check the 5050 manual for the instructions. Seems like the same line of receivers after all...

I have not done anything to the transistors. The dc offset is just below 30mv though. That's my reason for readjust everything.
 
P. S. said:
The dc offset is just below 30mv though. That's my reason for readjust everything.
Click to expand...
again just check the Bias first, generally no adj. is required if outputs haven't been replaced but worth a check anyway.
DC offset at 30mv L/R is acceptable if adj. isn't possible.
 
It seems like the STA-5010 amp board has similar layout to STA-5050. Not sure about the component values though. Anyway - I decided to perform similar bias procedure as suggested earlier in this thread.

Description in service manual is pretty vague. I am not sure I did this right so please don't assume this is correct procedure (use on your own risk and read service manual 1st ;-).
Here's what I performed - maybe somebody will find it useful or correct me:

Turned off receiver, and detached from power. Put deoxit to the trimmer resistors and worked them several times. Let it sit until dry. Turn on the receiver.
In my case the adjustable bias resistors were at 20mA all the time (measured between leg of resistor and ground) so I went ahead and moved to checking terminal DC voltage. The manual does not mention measure points - but looking at the board - there are 2 pigtails soldered right next to the resistors for each output channel. I marked them on the photo I attached (please bear in mind this is STA-5010 amp board photo - not STA-5050). I attached multimeter to the pigtails and was able to set DC voltage to 10.9 mV by moving the bias trim pots.

After that was done. I adjusted the DC offset trim pots and was able to get down the offset to a fraction of mV in each channel.
I turned off the receiver and let it cool down ,turned on and then rechecked all the measure points.

Right now:
Receiver runs warm but not hot and I can hear improvement in sound - probably mostly due to cleanup of the trim pots.


Thank you all for help
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IMHO the trimpots that nikko used are not very good, and can cause weird intermittent problems. Upgrading them is a good idea if you plan on keeping or restoring the receiver. My 2 cents....
 
Did not know that. The receiver is fully recapped already - I used Nichicon brand. I will add the trimpots to my further improvements list. The receiver is very well laid out and easy to work with. Some other "upgrades" I am considering:
- bypass film capacitors for the power caps
- use Wima film caps instead of electrolytics for all values below 1uf (I already did this with my NAD 7225 for phono stage and tone board with quite good result - way more detail in sound)
 
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