Alignment of Integrated Amp

[Balthazarr]

Is it best to set idle current first before DC offset or doesn't it matter?
I did offset adjustment, but wondering.

Now I'm warming up the unit again bc it took me such a long time to find the TP's if indeed I have.
Trace doesn't fully resemble my drawing and concerned I don't have the right points.

Any general rule of thumb to differentiate?
Tough to see even with dedicated lamp.

[Balthazarr]

So one slip of the test probe and now one channel out and the one that is working has a hum until protection circuit shuts everything down.
Head phones out work fine as expected.

Is it likely I have more than an output trans dead?

Wish I'd left the idle adjustment alone.

[bolly]

you should read here (http://audiokarma.org/forums/showthread.php?t=5634&highlight=offset) Balthazarr. :yes:

[EchoWars]

Perhaps that is the root of the problem.

Whatever is busted can be fixed. You didn't mention what the unit is.

Still, likely have smoked some outputs, depending on what got shorted. But you say that the HP jack works. Odd, since most HP jacks are driven from the output of the amp, with a simple dropping resistor in series to knock the voltage down.

[Balthazarr]

Bolly, thanks for the suggestion, but reading THERE is what got me into this mess.
A little knowledge is a dangerous thing and guessing is worse in my case.

So here is what happened.
Difficult to read diagram had to transpose locations in my head when I inverted the unit to access tp's to adjust for idle.
Sure I had found them, I proceeded to measure and adjust. Unfortunatley, a lapse in concentration allowed my probe to short to solder points in close proximity.
Sparks flew and I continued with idle adjustment.
After completion (or so I thought)-hooking up spkrs and deck to test I get a pulsation in rt channel accompanied by hum which is visible on LED panel.
Left channel is not working (at least the spkr wasn't), I hear relay clicking (very hard of hearing so had to put my left ear up to unit).
Each click shows up as pulse on meter.
So I'm thinking I must have fried something with that little fireworks show.
HP exhibit same symptoms although earlier I guess I was a little hasty in diagnosis so I posted in panic mode saying HP o/p worked properly.
You are right EW, mine is the same as any other amp.
Switched spkr not working r and l banks same problem. Spkr wouldn't fire. LT spkr would work, but selecting A or B would show problem dependent on which bank the
rt spkr was hooked to.
So, after scratching my head and fearing the worst, I envisioned trying to find a new trans and maybe a few other parts for my NAD 3140.
Not to mention the downtime and shame that I was sure to feel after thinking I could do this simple job myself.
Finally, I reached behind the rt spkr and tugged on the leads at binding posts on Heresy and the damn thing came to life.
Somehow I had managed to allow the uninsulated portion of wiring to contact each other shorting the spkr.
It had nothing to do with the light show afterall.
Glad to know my protection circuit works.
Realigned in newfound relief and cranked it up for a few seconds.
Now I can concentrate on playing with my new toys from ebay when they arrive.

Thanks for responding to my cries for help, I fully appreciate it.
I have an awful lot to learn.

[EchoWars]

Wow! Wierd problem...

I'm happy that all seems well now. Always depresses me when someone reads that thread and gets into an amp and something lets go.

Glad you are running! Be careful out there.... ;)

[webbb]

Balthazarr,
Do I understand that this is a NAD 3140 amplifier?
Do you have schematic or diagram/instructions for setting idle and dc offset?
I could not find the schematic for mine, so I did not try it (it needs it). The four pots that I remember finding did not have any logical connection visually and I did not want to make sparks....
But if you have a diagram I would love to get a copy !
Thanks
B

[Balthazarr]

Webb,
I can send a copy of manual, but I can't guarantee the quality as I received this from NAD in early 90's and it is a xerox of their manual and not a good one at that.

There are 6 pots if you count LED meter adjustment.
The latter are on the panel board behind the readout.

The 4 I needed for idle and offset are clustered in one group of 3 (VR601,602 and 604) and VR603 is separated. (To left if looking from above front)
601 and 602 will give you the offset. VR 601 is underneath some shielded bundles next to VR602 and VR604.
VR603 and VR604 are for idle current.

All 4 are where the output trans are located at rear edge of board. (SCXXXX or another alpha numeric).

For idle adjustment (unit off and cold) set both 603 and 604 fully cw (ccw for me upside down) and disconnect spkr (no load at terminals) also set Vol to 0.
Turn on and let heat for about 5 min
Using A+B setting on spkr selector, place probe of DVM (setting in mv dc) in + of Left speaker terminal and find tp 1 for left channel.
Best to find tp's first. lol
You can find tp 1 by counting over to second trans (there will be a small one first) and place 2nd probe tip on the last leg of 2nd one (emitter). If you choose any of the other 2 legs you will get an over-reading. Way over. I did and meter showed a lightning bolt in display.
Set to 6 mv (don't worry about a neg reading-probes are reversed if you get neg)
Do the same for Rt channel: probe in + of rt spkr and tp 2 located on leg closest to VR604 (to the rt if looking from above front in normal orientation)
I had to invert the unit to use the trace layout to locate tp's from diagram so everything from left to right was rt to left.
In the diagram the pots are superposed on the trace on bottom of PCB, but you can adjust if you know where the emitter legs are without turning unit over.

I let cool down between dc offset and idle adjustments even though idle is presented after offset in manual.
I figured setting VR603 and VR604 to max cw done prior to heating up by manual instructions that it be best to do each set of adjustments as if unit was previously unused.

HTH

If i made a mistake on the general approach, please feel free to correct.

[Balthazarr]

Where in Socal are you?

I can try to scan the pages for you and hope quality is good enough to send via email or just make a copy and send snail mail.
LMK how you want to proceed.

BTW, the aforementioned instructions are from a novice so best to wait until either confirmed by knowledgeable member or you receive a copy from moi.