Recapping Vintage NAD Receiver (7150)

[brada220]

I am beginning a new project regarding my 30+ year old receiver I have owned since day one. Due to amp in one channel going out I openned the case up and found a number of blown caps in the audio and tuner boards. I will be purchasing a new intergrated amp shortly, but I want to "play" around with my NAD just for experience sake.

I gotten the boards seperated from the case and will be sending for replacement caps (Mostly Elna caps) - however, I need advice on how to best remove the caps from the board - When one turns over the board there are no indicators on the board what device is on the other side - I do not want to be de-soldering any other item than caps - so how does one go about removing the caps without mistakenly desolders some othe device, say like a transistor?

I have downloaded the service manual but I do not find it to be much assisstance with helping to locate the caps from the underside - any recommendations as to best method??

 

[Bob]

couple of suggestions

1. try finding a parts layout picture (many service manuals have this - don't know if the 7150's SM has)
2. take a good picture of the components side

then grab the jpg or crop of the SM's parts layout and using a photo editor, flip the image left to right.
this puts the component side in the same (mirror) image as the solder side. size to match the board
(you can adjust the size through the photo editor and/or printer parameters). and have
rulers on all sides.

or doing it the hard way

1. mark the edge where there's a cap nearby, go perpendicular to the edge and measure the offsets
of the two pins from the edge. flip board over, go to the marked edge and use that offset to find the
two legs.
2. if the cap is in the middle of the board. do #1 but put a edging piece of masking tape
(peelable without leaving glue - comes in green or blue) across the board on top and bottom
with the tape on one side of the cap (and from the same side on the bottom). then measure
off the component from the edge and do the same on the bottom.

or if you're very flexible (and your equipment is even more)
1. mount board on pivotable clamp (ones you see holding up a PCB so you are hands-free)
2. shine light on one side, mark with marker on that side, and view the other side and mark
its bottom-side counterpart location.

or all three.

I use the top method for a variety of reasons, the first set of "prints", identify the resistors
I replace, then the second set is marked with the caps, etc. the idea is that you do the
resistors first since they are closer to the board, etc. and the trick is that you can see
the new resistor solder joints (vs the older "standard" factory joints) and avoid a
unnecessary de-solder.

see my guides for upgrading the haflers. On the dh101 I replaced all the original
carbon resistors with metal films, then got rid of the tantalums, ceramics, and most of
the electrolytics.

since you have them out of the unit, you are far (better) ahead than me - I left the boards in
hence I had to rotate the entire unit, not as easy as just the board.

good luck -- and please document with text and pictures as a way to help others in the future.

 

[teal'c]

I do not want to be de-soldering any other item than caps

Who does?
It's going to happen.
I used a bright light or sunlight and the shadow of my finger (occasionally a pencil on the crowded spots) on the component side for a lot of mine. A voltmeter with a continuity tone was helpful IDing other part's solder pads around the caps.
By the end of the board I was recognizing patterns and placements and could find most spots without too much trouble even without the lighting.
Practice, practice, practice.

 

[dzkfraser]

I read somewhere that a laser pointer would help by shining on one side of the board and noting where the light filters through the board on the opposite.

 

[brada220]

Thanks for the valuable suggestions - never thought of most - thanks again