Replacement output caps for 1992 NAD 5425 CDP

inspiredsports

I just received a very, very clean 1992 NAD 5425 CDP that I purchased from the original owner complete with manual, box, working remote (and even a CD left inside) for $34

It looks and sounds great, but I tore it apart as my intent is to experiment on this puppy with a with a tubed output amp.

The Output Caps look leaky to me, but I'm enough of a newb to not even know for sure

The originals are "Elite" brand 25V 2200uf.

Can anyone make a good recommendation as to what I can replace them with ??

Systems

Are you certain they are the output coupling caps and not for power supply decoupling?2200uf is extremely large for outputs, the usual values are in the 10-100uf range.Hard to tell from the pic but they may be leaking or that is epoxy used to reduce vibration.Is the brown gunk hard or soft?

inspiredsports

Thanks for being so polite! I'm a quick study, but truly new at the internal side of electronics.

They are the biggest caps on the board and just downstream (within inches) of the fuses and voltage pins where power arrives to the board from the power supply.

I then found the op amp circuits (clearly pairs) feeding the RCA jacks wherein the true, much smaller output caps are located.

The goo is in fact very hard and resembles what is apparently painted over the wire coils in the power supply.

I did not know they routinely use epoxy like this so I've learned something today.

That's what had me baffled as NAD is known to use high quality components, plus, the sound quality and width of the soundstage from the unit is very, very good which didn't make sense if the caps were "bleeding out".

I have more pics, but I think you have tactfully led me to the right answer.

Thanks,
Greg

Systems

inspiredsports wrote: »

Thanks for being so polite!

Your welcome Greg,and what reason would I have to not be.btw.nice snag for $34.

I then found the op amp circuits (clearly pairs) feeding the RCA jacks wherein the true, much smaller output caps are located.

There are lots of options for replacements preferably a film cap of some sort,but board space may limit your choices.By all means upload more pics.

I did not know they routinely use epoxy like this so I've learned something today.

Many Asian manufacturers use it at the base of electrolytic caps to reduce vibration so reducing the likelihood of the leads separating from the plates.Some times they are less than neat when applying it.

inspiredsports

Here are a couple more photos (taken quickly). I'll set up my photo tent and lighting when I pull the board for modding so better quality photos are coming.

The power supply is a decent (EWE?) QR575007 iron and copper 18-0-18, and op amps (2 of 4 shown) are Signetics NE5532N, but this is where bypassing with a tube rig is calling.

The second photo is a better shot of showing where power comes in to the board.

sucks2beme

A common mod is to replace the power supply diodes with FREDs
(fast recovery diodes) of similar ratings. Fast and cheap mod.

Systems

inspiredsports wrote: »

and op amps (2 of 4 shown) are Signetics NE5532N, but this is where bypassing with a tube rig is calling.

You will most likely need atleast one of the 5532's per channel as in all probability it is( depending on DAC chip used) either the current to voltage converter,or the buffer for the low pass filter. If the 2nd one is just a straight buffer to drive the output,thats were the tube stage will be best inserted.A schematic would be very helpful.If I get some time I will look on line for one.



What DAC chip does it have?Philips,Burr Brown?

inspiredsports

GV#27 wrote: »

You will most likely need atleast one of the 5532's per channel as in all probability it is( depending on DAC chip used) either the current to voltage converter,or the buffer for the low pass filter. If the 2nd one is just a straight buffer to drive the output,thats were the tube stage will be best inserted.A schematic would be very helpful.If I get some time I will look on line for one.

What DAC chip does it have?Philips,Burr Brown?

Obtaining a schematic is high on my list. I've found them online for about $16 but haven't pulled the trigger yet.

The DAC chip has me baffled. Every reference list I've ever found shows it should be an MN6471M (Wolfson; Scotland).

I spent over an hour last night with a high-intensity light and magnifying glass identifying the various chips and transistors.

There are 7 chips in the board. 4 are the Signetics NE5532N's in the op amp circuit.

There is a 16 pin chip marked 829400 M5290P (it has a 3 pronged logo forming a triangle (Mitsubishi ??)). The last 2 chips are mounted VERTICALLY with I believe 8 pins on each coming only out of the bottom. One is a Toshiba TA7256P (Japan 9041K) and the other is marked SK 0019 STA341M.

There's nothing in there showing the expected MN6471M :mad:

Systems

inspiredsports wrote: »

Obtaining a schematic is high on my list.

Yes highly recommended.

The DAC chip has me baffled. Every reference list I've ever found shows it should be an MN6471M (Wolfson; Scotland).

Yep its an MN6471 1 bit MASH chip.It's a surface mount device hidden on the bottom side of the main board.I found a pic.

inspiredsports

GV#27 wrote: »

Yes highly recommended.
Yep its an MN6471 1 bit MASH chip.It's a surface mount device hidden on the bottom side of the main board.I found a pic.

You know, I suspected it was underneath. I haven't removed the board yet and looked through a tiny screw hole on the side, but couldn't see much.

The plot thickens: I bought ANOTHER 5425 of of eBay for under $40 delivered that needs the light bulbs in the display replaced. This apparently is a very common fault (but about the only one) with this model.

When it arrives, I am going to do some double blind referencing to determine if they sound essentially identical. If so, I will be in the very rare situation of having a "control" model against which I can compare my mods!

I'll be back posting when I have everything in place and tested (2-3 weeks).

Greg

Systems

Its nice to have a reference for easy comparison.I ended getting a second identical univeral player and did different mods to each. http://www.polkaudio.com/forums/showthread.php?t=55733&highlight=pioneer+dv563