This calamity tells us that you forgot to power up via the Mains Bulb Tester.
When are you going to listen?
Please chose the main fuse when something goes wrong that burn or smoke not the whole amplifier or worst.
Remember safety first!
are you sure?
What tests have to run to check for a shorted turn in the secondary?
Yes, there are tests you as a low resourced amateur can do to check for a shorted turn.
There's continuity on each windings and they all measure no more than 5-7ohms.
On 200k ohm setting I tested between all of the windings for shorts. The primary and secondary is completely open, and between all secondaries they measure between 700k-1M+ ohms.
I haven't tested whether they are putting out 28V as rated.
Secondaries should measure very low impedance (or DC resistance even) it sounds as though your transformer is toast.
(unless you mean that's the resistance between the two secondary windings)
So according to the image - you should have low DC resistance between 1 & 2, 3 & 4, 5 & 6 - but nothing between the rest. (assuming your transformer has dual secondaries)
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Yes I mean the resistance between the secondary windings.
According to the image,
low DC resistance between 1 & 2, 3 & 4, 5 & 6,
completely open between 1 & 3, 1 & 5,
and
700k-1M ohm between 3 & 5.
The high resistance between 3 & 5 is a worry - are you certain you're not measuring your fingers? (holding the probes)
I would try and get an insulation test performed before using it again.
You are probably right, it might have been measuring my fingers instead. The test probes don't have alligator clips so I pressed them against the wires with my fingers.
Here it says the windings should measure hundreds of megaohms or more between each other, but I only got kilo ohms.
Transformer tests
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Not sure if I can help here too... what is the current situation ? The transformer looks fine. Did the transistors get rewired to the correct pin-outs ? Does the circuit still not work - do you have updated voltage measurements around the circuit ?
Did the board get cleaned properly to remove the flux (you can use acetone or alchohol to remove regular rosin flux) and can you post a photo of the completed board ?
Are you missing key parts or have some that are suspect fakes ?
Did the board get cleaned properly to remove the flux (you can use acetone or alchohol to remove regular rosin flux) and can you post a photo of the completed board ?
Are you missing key parts or have some that are suspect fakes ?
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1) I hope the transformer is fine, I'm gonna need to do some electrical tests on it and see if there's any leakage, shorts, or open circuits when there's power.
2) The transistors with the wrong orientations have been rectified.
3) The transformer only disconnected on the right channel. Left channel is left intact and last time I measured it was within 1-3mV from Algar's measurements. I will need to check again after I go through the parts in the circuit to see if there are other damages.
4) I always clean using electronic cleaner after soldering/desoldering and brushing them with a toothbrush. I'll post a photo when I get home, there are some solder points that had peeled off from the board, doesn't look very pretty. I think it's because my soldering iron is too hot. I'll need to invest in variable temp stations. A new board is probably due, so I might get this new updated board.
ZEROZONE】黑匣子 直刻naim后级NAP200功放板-PCB 2.0 加厚版-淘宝网全球站
5) I've replaced all transistors and capacitors with genuine parts except for 2SC2922. Those are confirmed fakes after comparing with genuine pictures. I'll replace it probably next month.
Hi,
Last month I'm bored and wanted to build something and I found zerozone nap-140 clone boards and ps pcb.
Followed 140 schematics and used sc2922 sanken outputs and 32v rails.
But somehow I cannot adjust bias at all.
Pot has no effect. Drivers (onsemi 15030&31) and outputs are all checked ok. When I try to measure bias at positive rail its around 17mA and does not change at all.
What am I missing?
Where to check?
Thanks..
Last month I'm bored and wanted to build something and I found zerozone nap-140 clone boards and ps pcb.
Followed 140 schematics and used sc2922 sanken outputs and 32v rails.
But somehow I cannot adjust bias at all.
Pot has no effect. Drivers (onsemi 15030&31) and outputs are all checked ok. When I try to measure bias at positive rail its around 17mA and does not change at all.
What am I missing?
Where to check?
Thanks..
The procedure has been posted many times in this long thread but the burning question is 
- what and how are you measuring the bias current? You are looking to read only 5-7 mV across either large 0R22 resistor that connects directly to the output transistors. That is, to the emitter of TR11 and the collector of TR12. Don't confuse these resistors with the identical one that connects directly to the output terminal, as all 3 have a common connection but you'll read nothing useful there.
The measurement is a very small one and of course, requires a sensitive DMM set to the lowest DC voltage scale and don't connect any output or input to the amplifier (i.e. no speaker, no signal) whilst setting bias.
- what and how are you measuring the bias current? You are looking to read only 5-7 mV across either large 0R22 resistor that connects directly to the output transistors. That is, to the emitter of TR11 and the collector of TR12. Don't confuse these resistors with the identical one that connects directly to the output terminal, as all 3 have a common connection but you'll read nothing useful there.The measurement is a very small one and of course, requires a sensitive DMM set to the lowest DC voltage scale and don't connect any output or input to the amplifier (i.e. no speaker, no signal) whilst setting bias.
Re: New Board
If you plan to reuse the resistor on the new board, make sure the board thickness are the same.
Otherwise, reused component pins maybe too short.
There are two versions of the board with different thickness, 1.6mm and 2.0mm, RMB 60 and RMB 100, respectively.
By the way, thanks for the transformer wiring check.
I found a very good transformer manufacture recommended by HiFidiy member.
And it is located in Connecticut, US. 2 hour from my house.
Compared to the one build in China, US$ 20 more for the transformer . Probably $20 less for shipping. No need to ride on 747/777.
If you plan to reuse the resistor on the new board, make sure the board thickness are the same.
Otherwise, reused component pins maybe too short.
There are two versions of the board with different thickness, 1.6mm and 2.0mm, RMB 60 and RMB 100, respectively.
By the way, thanks for the transformer wiring check.
I found a very good transformer manufacture recommended by HiFidiy member.
And it is located in Connecticut, US. 2 hour from my house.
Compared to the one build in China, US$ 20 more for the transformer . Probably $20 less for shipping. No need to ride on 747/777.
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I've learned my lesson after that catastrophe and connected the light bulb current limiter. Couldn't find a 100W or 75W so I got a 60W. It still works fine though.
Transformer also works fine still, no smell no shorts. I guess I turned the power off quick enough.
However the faulty channel has a 30mV± DC offset while the ok L channel has about 1-5mV± offset. Is it too much of a difference?
I tested the rest of the components; transistors caps and resistors all are still fine except for the obvious burnt 0R22's.
Measurement with algar's circuit again yields within 1-2mV from his measurements.
Transformer also works fine still, no smell no shorts. I guess I turned the power off quick enough.
However the faulty channel has a 30mV± DC offset while the ok L channel has about 1-5mV± offset. Is it too much of a difference?
I tested the rest of the components; transistors caps and resistors all are still fine except for the obvious burnt 0R22's.
Measurement with algar's circuit again yields within 1-2mV from his measurements.
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Re : 2922
You should never power up the board without the heat sink for 2922.
Improper static current setting, or even oscillation, could ruining the transistors.
You should never power up the board without the heat sink for 2922.
Improper static current setting, or even oscillation, could ruining the transistors.
I think it is safer/better to start with a low wattage bulb, either a 28W, or 40W
That looks like you need further investigation.
It might be an overloaded resistor that has changed value.
I wrote that years ago in this thread, but it's obviously hard to read through it. It's very big now, so I'll repeat it for all people building this kit:
You should never power up this board with the power transistors!
First power-up should be with the drivers only. The circuit works fine on drivers only and output floating (no load)
That has several benefits:
1. If something burns, it will be cheap.
2. If nothing burns, but still the circuit is not working, you'll have generally more time to troubleshoot and measure before it fails permanently... In the worst case, something cheap will overheat and burn.
3. You can verify the whole circuit works - check output offset, check bias spreader work by turning the trimmer and measuring the voltage change between the driver transistors bases.
4. Leave the bias at something like 2V between base-to-base of the drivers. Then, add the power transistors and turn the trimmer up (by now you'll now what is the up direction) until current flows in the output resistors (5-7mV across). That's it!
Play some music.
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