Hi All,
I recently got a non-working NAD 326bee. It makes a loud buzzing sound through the headphones, regardless of volume. No music can be heard, only buzzing.
I went ahead and rebuilt most of the PSU board (all the capacitors, the two transistors, an optocoupler, and a DB105 IC). Theres a TINYSWITCH-III TNY274PN, another IC called DB104, and then several rectifier diodes that i didn't touch, only because i couldn't find the equivalents at Digikey. Mouser seems to have all but the tinyswitch, but i want to stop any more shotgun replacement and actually learn how to diagnose the thing.
When i power it on, i get buzzing (and blue power light) and then 2 seconds later the buzzing cuts off and i guess it goes into protection as i hear the relay click, and the blue light turns orange.
The DC volt readings at both speaker terminals are 0.005V right before the relay clicks.
I would like to go through the schematic and test for voltages here and there, but there are no voltages listed so i don't know what to do next, and need help.
Thanks for listening, and i look forward for guidance on where to start.
I recently got a non-working NAD 326bee. It makes a loud buzzing sound through the headphones, regardless of volume. No music can be heard, only buzzing.
I went ahead and rebuilt most of the PSU board (all the capacitors, the two transistors, an optocoupler, and a DB105 IC). Theres a TINYSWITCH-III TNY274PN, another IC called DB104, and then several rectifier diodes that i didn't touch, only because i couldn't find the equivalents at Digikey. Mouser seems to have all but the tinyswitch, but i want to stop any more shotgun replacement and actually learn how to diagnose the thing.
When i power it on, i get buzzing (and blue power light) and then 2 seconds later the buzzing cuts off and i guess it goes into protection as i hear the relay click, and the blue light turns orange.
The DC volt readings at both speaker terminals are 0.005V right before the relay clicks.
I would like to go through the schematic and test for voltages here and there, but there are no voltages listed so i don't know what to do next, and need help.
Thanks for listening, and i look forward for guidance on where to start.
Attachments
I checked the J601A / J601B connector's voltages, and found something interesting. The 22V rail, from standby, reads 22V, but when i power the unit on, it mumps to 38V.
It seems that the DB104 IC provides the 38V rail voltage.
Why is this voltage getting mixed-in with the 22V rail when i press power on and the relay clicks?
It seems that the DB104 IC provides the 38V rail voltage.
Why is this voltage getting mixed-in with the 22V rail when i press power on and the relay clicks?
Are you able to measure current flowing into the amplifier through a limiting device? A lightbulb would do. At this point it'd be favourable to avoid too much stress. If the current measured is very high then testing the output devices might be necessary to eliminate or diagnose an output short.
When you say the headphones output doesn't work, does that mean the speaker ones do?
When you say the headphones output doesn't work, does that mean the speaker ones do?
I don't have a lightbulb / limiting device to test with. I'm moving on Sept. 1 and have already started packing everything up!
I will go ahead and test the 4 main output devices this evening.
The buzzing comes through the headphone output. I have not connected the speakers since the headphone buzzing was so loud.
Also, if a moderator is reading this, i meant to post this in the solid state forum, but was reading a Pass Labs post, and used the wrong window to create this thread. Please move it to Solid state when you get a chance, thanks!
I will go ahead and test the 4 main output devices this evening.
The buzzing comes through the headphone output. I have not connected the speakers since the headphone buzzing was so loud.
Also, if a moderator is reading this, i meant to post this in the solid state forum, but was reading a Pass Labs post, and used the wrong window to create this thread. Please move it to Solid state when you get a chance, thanks!
I found a broken trace under the power board and bypassed it with a piece of wire. The unit is now out of protection and makes a constant "analog" buzzing sound. It definitely does not sound like a ground loop hum.
If you have blown off tracks then it sounds like a short somewhere.
Maybe an output transistor(s) gone ?
Maybe an output transistor(s) gone ?
It looks like this unit has had multiple repairs in the past. There are many lifted/destroyed traces on the bottom of the mainboard, through-hole diodes replacing SMD ones, bypassed traces...strange solder blobs to bridge lifted traces.
Even when i was redoing the PSU board, and ever so gently using solder wick, the traces would lift right off...even though they were under a layer of lacquer?!
I think the best course of action is to abandon the ship here, and get on board with a DIY power amp from this thread!! Hopefully i can reuse the transformer and PSU board from this unit!
Even when i was redoing the PSU board, and ever so gently using solder wick, the traces would lift right off...even though they were under a layer of lacquer?!
I think the best course of action is to abandon the ship here, and get on board with a DIY power amp from this thread!! Hopefully i can reuse the transformer and PSU board from this unit!
