NAD 319 rebuild project

[cviller]

Hi

I have an old nad 319 amplifier, which unfortunately is completely screwed up. The protect circuit would not turn off. In the beginning, it was only the relay that messed up the signal, but when I got that fixed, the voltage wouldn't drop on the TA7317 (protection circuit). After days of soldering measuring and burning components, I have come to the conclusion that I need a new psu-pcb. The only thing keeping this pcb together is the soldering mask. There is a +/-67V and a +/-60 V on the board. The 60V, which supplies the emitter-followers appears to be very stable, but the 67V running the protect circuit and signal amplification is very unreliable. This is the bottom view of the pcb:



(I have added some resistors to discharge the capacitors, while trying to fix it).

The question is: Do you think I should try to make an exact copy of the old layout or should I just make sure the connectors are placed correctly?
Before I start my pcb program - has anyone else done this before? The pcb is the same as the one in nad 317.

Regards
Christian

[Leolabs]

To be place safe,follow the old layout

[pinkmouse]

I would ask myself, is it really worth rebuilding?

[cviller]

I think it is worth rebuilding, because I really liked the sound when it worked.
I know there are many in here that don't like nad, but besides the bad pcb quality, I think it is a matter of taste and I think the sound is very good compared to the price.

I have another question. In the 67psu, there are some 100 Ohm fusible 1W resistors that died during repair.

The part of the schematic with these resistors can be seen here:
Part of psu schematic

I can't find the components in Denmark. Do you guys think it will safe to use regular power resistors?
Some of the resistors in the amp are "flame proof". Are most power resistors not flame proof?


Christian

[Tube_Dude]

Originally posted by cviller


I have another question. In the 67psu, there are some 100 Ohm fusible 1W resistors that died during repair.

I can't find the components in Denmark. Do you guys think it will safe to use regular power resistors?
Some of the resistors in the amp are "flame proof".

Hi Christian

If you can't find "flame proof" resistors , change the R203 FP resistor for the place of the R205 resistor and use a regular resistor in the place of R203 , because this last one , is not in a so critical position , as R205 , in case of a short in the + 67 Volt rail.

Cheers

[cviller]

I have finished the all the layout work. I might change something before i do the actual pcb, but it won't be much. It took me forever, because I had to draw schematics and footprints also.

Tube dude: Thank you very much for providing a solution. It was not flame proof, but fusible, but the idea of using ordinary power transistors for the none critical parts should stil be valid.

I really hope I can make it work now. Someone interested in the pcb.ps when it's working?

[Kärpänen]

I have also problems with 319 psu, and might be interested in making a new pcb. If you have finished with the layout, I'd be very glad to get that as well.

Thanks a lot and regards,
Petri

[cviller]

I did complete the layout and I found only one mistake (the schematics from the service manual had some errors). I can correct that mistake and give you the layout. I've done the layout using the GPL program called "pcb", but I can export to ps, pdf and gerber - whatever you prefer.

[Kärpänen]

I think pdf is the best choice, I can be sure that I will get it opened.

[cviller]

I have placed the pdf ps files here:
PCB and schematics
(The files won't be there forever, but mail me if they are gone and you need them)

I recommend using the ps files if you have access to a postscript printer, but the pdfs should also work.

Use of this layout is at your own risk. I cannot be held liable for any damages to humans,property,animals etc., caused by using the layout. Nadelectronics holds the copyright for the schematics and layout structure. This is a reproduction of the psu-pcb and only intended for repair purposes.

The layout does work for me. The sound appears to be like before - no distortion. An important thing to do if you plan to use my layout is to make sure that there are no shorts. I had some shorts I needed to scratch away using a knife, but it might have been because I didn't gave the board enough time in the developer-fluid.
I have made most of the drill holes smaller than they should be to make sure the solder pads would be completely covered with copper, but if you do the pcb drilling your self, you can just look on the original pcb.
My program does not have a symbol for all those shorts on component side, so I have drawn them on the componentside as copper traces. You'll need to print the component side to get those locations. All components and shorts are placed very close to the original, so you can just take one at a time.
I think it is a good idea to start with all the psu stuff for the 5V, +-60 and +-67, and then make sure you have the correct voltages and no smoke.
Remember to discarge the big capacitors before you start soldering!

Why do you need to make a new pcb? Is it because the the solder pads are falling apart?