Hi all,
I've got a non functional NAD 304 for free in order to repair it.
The owner said that it suddenly stopped working in the middle of a party.
I thought it'd be a simple fix like a power supply issue/fuse or even some kind of overload protection kicking in because of a short but it turns out I might have an open primary on the power transformer.
I desoldered the secondary of the transformer going to the board and tried to power it up with no luck.
I even tried to power it up (with a lamp in series) directly from the primary (bypassing the switch) but again no signs of life.
I get absolutely no ohm reading (OL) between the red (hot) and neutral (black) of the primary.
The transformer has other windings for 110V operation but I only tried the 220V so far.
I might try the 110V taps too which might be okay but I'm very curious what might be the issue here.
I opened up the transformer (broke the external shield plate and removed the insulating tape) and nothing seems or smells like it's burned up.The enamel wire seems okay so I suspected a thermal fuse might have opened.
Thing is there is no thermal fuse there (not within reach anyways) so it's kind of strange that the transformer primary "opened" with no signs of overheating etc..
Does anyone know if that's really the case with these amps?
I've got a non functional NAD 304 for free in order to repair it.
The owner said that it suddenly stopped working in the middle of a party.
I thought it'd be a simple fix like a power supply issue/fuse or even some kind of overload protection kicking in because of a short but it turns out I might have an open primary on the power transformer.
I desoldered the secondary of the transformer going to the board and tried to power it up with no luck.
I even tried to power it up (with a lamp in series) directly from the primary (bypassing the switch) but again no signs of life.
I get absolutely no ohm reading (OL) between the red (hot) and neutral (black) of the primary.
The transformer has other windings for 110V operation but I only tried the 220V so far.
I might try the 110V taps too which might be okay but I'm very curious what might be the issue here.
I opened up the transformer (broke the external shield plate and removed the insulating tape) and nothing seems or smells like it's burned up.The enamel wire seems okay so I suspected a thermal fuse might have opened.
Thing is there is no thermal fuse there (not within reach anyways) so it's kind of strange that the transformer primary "opened" with no signs of overheating etc..
Does anyone know if that's really the case with these amps?
The black wire does not have continuity with any other wire indeed.
Black is the only wire that looks like it's not connected directly to the magnet wire and I've tried to pull it out to see to what it's connected too(hoping to be a fuse) but unfortunately I broke it
The other end is deep inside the transformer so I guess I'm screwed.
Whoever made that transformer didn't really want anyone to fix it if it fails I guess..
I've seen transformers with their fuse easily accessible (just under the insulation tape), this one probably had the fuse to protect only the user and not the transformer itself.
I might have to make a new transformer for this if the cost is not too high.
But I don't think that's possible without knowing the amperage ratings of the individual secondary taps..
Black is the only wire that looks like it's not connected directly to the magnet wire and I've tried to pull it out to see to what it's connected too(hoping to be a fuse) but unfortunately I broke it
The other end is deep inside the transformer so I guess I'm screwed.
Whoever made that transformer didn't really want anyone to fix it if it fails I guess..
I've seen transformers with their fuse easily accessible (just under the insulation tape), this one probably had the fuse to protect only the user and not the transformer itself.
I might have to make a new transformer for this if the cost is not too high.
But I don't think that's possible without knowing the amperage ratings of the individual secondary taps..
Attachments
I would think carefully before taking on a project like this. The service manual shows it is designed for high peak envelope power of about 120W from what is only a 35W RMS continuous rated design. There are two power supply voltages, the higher one switching in to permit the peak power for transients. There is much to go wrong there, apart from your transformer probably needing a rewind - an expensive one, I think.
I hazard a guess that the main secondary windings would be 2 x 36VAC in series, tapped at 25VAC each. That is, 36-25-0-25-36VAC. It is only a 35W/channel 8R rated amplifier though, so it takes its rating from the lower voltage supplies of about +/-35VDC. On lower impedance loads, I couldn't guess how much more power was available. Knowing NAD's reputation for minimal power supplies, the transformer might not rate more than about 180VA.
NAD 3020 - Manual - Stereo Integrated Amplifier - HiFi Engine
I hazard a guess that the main secondary windings would be 2 x 36VAC in series, tapped at 25VAC each. That is, 36-25-0-25-36VAC. It is only a 35W/channel 8R rated amplifier though, so it takes its rating from the lower voltage supplies of about +/-35VDC. On lower impedance loads, I couldn't guess how much more power was available. Knowing NAD's reputation for minimal power supplies, the transformer might not rate more than about 180VA.
NAD 3020 - Manual - Stereo Integrated Amplifier - HiFi Engine
Sorry, wrong manual (funny, I selected 304 and got that??)
NAD 304 - Manual - Stereo Integrated Amplifier - HiFi Engine
NAD 304 - Manual - Stereo Integrated Amplifier - HiFi Engine
Check if you have continuity from,
- WHITE(pin 15?) to BROWN(13)
- WHITE to YELLOW(12)
- WHITE to RED(11)
The WHITE and BLACK wires are at the same potential, connected by
the fuse. You could bypass the fuse by moving the return power cord
wire (Neutral) from Pin 15(BLACK) to Pin 14(WHITE). From a safety
point of view this is not on however in theory(?) it should work.
- WHITE(pin 15?) to BROWN(13)
- WHITE to YELLOW(12)
- WHITE to RED(11)
The WHITE and BLACK wires are at the same potential, connected by
the fuse. You could bypass the fuse by moving the return power cord
wire (Neutral) from Pin 15(BLACK) to Pin 14(WHITE). From a safety
point of view this is not on however in theory(?) it should work.
I bypassed the black wire and the amp now works!
Thanks..
Should I maybe put a slow blow say 1 amp fuse between the white and red?!
I don't know at what amp draw the thermal fuse should open; maybe try to simulate that draw with a 4ohm load and measure temperature inside the transformer?
Or it's just easier to try different fuses at different volumes
Thanks..
Should I maybe put a slow blow say 1 amp fuse between the white and red?!
I don't know at what amp draw the thermal fuse should open; maybe try to simulate that draw with a 4ohm load and measure temperature inside the transformer?
Or it's just easier to try different fuses at different volumes
Remove your bypass modification, return the wiring to original, and connect a 1 Amp slow blow fuse from white to black wires. This assumes a 230VAC mains. The back panel of the amplifier lists power as 230VA so the first fuse to try is 1 Amp. If that opens due to start-up surge or other peak power demand, try 1.5 Amp or 2 Amps. If powering from 120VAC, double the fuse rating.
That's what I've also suggested to the owner. I've told him that it is fixed and he can take it back but only for casual listening.
If he decides to leave it to me could anyone recommend any quality speakers that go well with this amp?
I've used borrowed speakers for testing purposes but I don't have any passive speakers around ; only active monitor speakers.
If he decides to leave it to me could anyone recommend any quality speakers that go well with this amp?
I've used borrowed speakers for testing purposes but I don't have any passive speakers around ; only active monitor speakers.
