NAD AMP.....sound distorted....fuses blown

[linton]

hi there, this is my first ever post !!!

I got the amp second hand, so I dont know its history.....

When connected up, it powers okay, but when you play a CD/record the sound is distorted......

when i looked inside, 2 of the interal glass fuses were blown....I replaced them and it was okay for a short while, but its happened again......

does anyone know what might be causing this, whether there might be a chance i could fix it myself......(I dont play the amp loud).....

thanks alot....

 

[poynton]

The distortion is obviously because the fuses are blown. The amp is not operating with the correct voltages when the fuses are blown.
Replacing the fuses gives correct operation until they blow again.

So, what is causing the fuses to blow.??

With the volume down and no input,

!. do they still blow ??

2. Look inside for signs of overheating near the output transistors.[burnt components or circuit board].

3. Does 1 or more of the output transistors get hot / hotter than the others ??

What model is the NAD ??

Andy

 

[Gold_xyz]

can you read the model of amplifier ?
what name have the burnt fuses? F1 or F2 ?
this is written on the pcb... perhaps

caution with high voltage

bye

 

[linton]

Thanks GOLD XYZ & POYTON...

Thanks GOLD XYZ & POYTON...

the amp is a NAD 3020e

I cant see F1 or F2, they look like P503 & P505....

I cant see any burnt components......

I will have to get some more fuses before I can test it again !!!!

andy, what would the output transisters look like ?? are they green & battery shaped ??

thanks again

 

[es44]

The output transistors are easy to recognise. The are sitting in the middle of the case, on a L-shaped aluminium.
4 shiny metal cases with "wings".

 

[Gold_xyz]

a schematics of nad3020 is posted on eserviceInfo
http://www.eserviceinfo.com/downloadsm/21315/NAD_3020.html

PSU : http://www.tcaas.btinternet.co.uk/nad3020ps.gif

on schematics i see 4 fuses on supply.
Fuse 1 and Fuse 2 = 1 Amp
Fuse 3 and Fuse 4 = 3 Amp

 

[linton]

FUSES.....

GOLD XYZ....hello.....................


i think it is Fuse 3 & 4.....(F501, F502)...but they are on the board it says T4A /250 V......

Not 3A ??

I think it is different because my amp is NAD3020e....... (e)...

 

[Gold_xyz]

Hi Linton

I have seen for schematics of NAD3020E but I have not found
anything
perhaps the "E" version is it differs only for some particular
but probably the schematics is almost equal.

The fuses surely supply the end stage and
I think that the end stage transistors should be verified.
On the original schematics (of 3020) the end stage transistors are
the 2N3055 & 2N2955

Check these transistor before replace fuses

Attention that the capacitor remain charged also when the amplifier
is disconnected from electricity

 

[es44]

You can find the service manual right here:
Nad 3020e
Good luck with it.
Ebbe

 

[linton]

GOLD xyz

Thanks for all your help....

Your english is okay/good.....

I dont have any technical knowledge !!

Do you know How I can I check the transistors ?? (in my amp, there are 2 x 2N3055 T8651 & 2 x MJ2955 T8706)

what does a capacitor look like ??

thanks for all your help/time.......

do you work in electronics ??

 

[Gold_xyz]

Hi linton

A first test of 2N3055/MJ2955 can be made with the multimeter
and you immediately can see if they are in short circuit.
http://www.allaboutcircuits.com/vol_3/chpt_4/3.html

Also some caps he could be to replace.
(an electrolytic capacitor)

An externally hosted image should be here but it was not working when we last tested it.

You try to ask the help of one technician friend of yours
(I have been working in the electronics for many years)

bye

P.S. Always unplug the apparatus before opening !