NAD 7140 No audio, Preamp problem? New AK'er

[mbz]

Do you think I need a "bigger" regulator? I'm thinking "more robust", like if it could handle more input level than 40v.

Short answer is no, if it all works as intended then all ok.
Most/all "fixed" regulators that I know of have a 40Vmax input (others will correct me)
There are adjustable units like LM117HV, LM317HV and probably others that are better. These require some hacking to add the extra components.

What else affects voltage to IC902?

The +/-24V supply is mainly to supply the OPAMP (IC601=NJM2043). If this is working OK then it will draw 6-8mA which will cause
the input voltage to IC902 to drop by about 3volts (to +36V or thereabouts). There is an outside chance that IC601 (opamp) has died
(I would be surprised) and this has eventually led to IC902 dying (>40Vdc) then Q904 failing. As always we need to get to the root cause
as to why IC902&Q904 have failed.

I checked +/- 43v rail too, just like the 24v IN/OUT checks, and they were fine. -42.8 to +43.1. That's the power amp side, right? and the power amp was working.

Yep, the +/-43 supply has it's own/separate "regulators", Q901,2,3 and IC901. They supply the power amp and speaker protection circuitry.

NADs are great to learn on but... If you stumble across a cheap yamaha CA-800, CA-1000, CA-1010 and CA-2010 then pick it up.
The CA-800/-1000 are a real pain to work on. The 1010 and 2010 are easier and preferred by most. Keeping in mind the significant
price difference between the NAD7140 and the CA-1010.

 

[tusntuk2]

About recapping this unit - I would expect to concentrate on the main power/amp board, right? I mean, I really don't want to get into the FM board for fear of misalignment, and I might even pass on the phono preamps, although they don't scare me like the FM does. Any suggestions for brand, one being more musical or more reliable, perhaps?

 

[mbz]

Any suggestions for brand, one being more musical or more reliable

Your not afraid of asking difficult questions, volumes could be written about "best" capacitors.

I really don't want to get into the FM board for fear of misalignmen

I try and stay away from receivers for that very reason, don't have the tools. However, the problem I have is why do we recap and
aren't the receiver caps also affect. OK, understand your concerns, however any caps on the power rails should be replaced, regardless
of location.

My 2 cents on cap recommendations for a NAD would be along these lines, the goal is for best audio outcome NOT longevity...
Main filter caps Nichicon KW,... better than Nichicon KG type 1&2
C928,9 10000/50 KW's
Other power supply caps, Nichicon PW, eg C905.6, 7,9,,
Bipolar power supply caps, Nichicon EP
Bipolar audio path, Nichicon ES
audio path, Elna Silmic II's
local power resevoirs on phono, preamp,power amp rails, Elna Silmic II's
Noted that Rotel used black gates in their CD players for local opamp power supply
Low noise/leakage caps for phono/preamp (those orange ones usually), Nichicon KL, just about the only choice
Protection circuitry, Nichicon PW or whatever handy

If in doubt, Elna Silmic II's, Nichicon KL's or PW's

Stay away from MKS film caps for audio path, sadly MKP will not fit.

Nichicon KZ are very good however the Elna Silmic II's are better...

Most importantly, don't buy from ebay etc... only from a reliable source like mouser ...

I'm sure plenty will disagree/have their own views

I've recapped NAD 3150(x2), 3140, 3020(x3) have another 5-10 in the shed that need doing...

 

[tusntuk2]

Got the parts, put them in, powered up with the DBT and Bingo! Tuner came on and sounded clean. Actually, I had somehow pushed in the Tape Monitor button, so at first there was no sound and I was bummed - but then I remembered to check these things and switches, etc and success! I am planning to recap the main board, but in the meantime, oh my goodness, what a fine sound. So - many, many thanks to all who had a helping hand, with a special shout out to MBZ for getting me started. It's great to share your hard earned knowledge with a rookie, really almost unprecedented these days, and I am much obliged for the help and the education. I'll stick around and let y'all know how the recap for the 7140 and the SX-727 are going. (Oh yeah, IN voltage for the IC902 was about +20 with the DBT in circuit.)

 

[leesonic]

Sorry I'm late to this party.

For recapping, if the cap is in the signal path, use a Nichicon KL. If you can squeeze a film cap in, use WIMA MKS2. Elsewhere, use Nichicon KWs except where things get hot, then use a PW. Opinions on caps are just that, opinions. Check for feedback on my restorations by searching for my user ID in the title of posts. Talk is cheap, real feedback from satisfied customers speaks loudest.

Lee.