Hi everyone.
I have a relatively new Vox Night Train NT15C1 that has not seen a ton of use, But a couple of months ago it started randomly turning itself off. I turned the amp on for the first time in a while today and it took about 20 min for it to happen again and from then on it takes about 2-3 min after I turn it back on to shut down again.
I noticed that the small fan at the back isn't turning on so it makes me think that this problem is a safety feature built into the amp to keep it from overheating.
Are there any amp techs on here who have experience with the Night Train?
Thanks!
I have a relatively new Vox Night Train NT15C1 that has not seen a ton of use, But a couple of months ago it started randomly turning itself off. I turned the amp on for the first time in a while today and it took about 20 min for it to happen again and from then on it takes about 2-3 min after I turn it back on to shut down again.
I noticed that the small fan at the back isn't turning on so it makes me think that this problem is a safety feature built into the amp to keep it from overheating.
Are there any amp techs on here who have experience with the Night Train?
Thanks!
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What checks have you done so far?
Does the power light work when in this condition?
Do the heaters go out?
Does the HT stay alive?
It is a very simple amplifier based roughly on the AC15.
There is no over heat protection apart from a non resettable thermal fuse within the mains transformer. When that goes due to overheating, it is permanently dead.
Does the power light work when in this condition?
Do the heaters go out?
Does the HT stay alive?
It is a very simple amplifier based roughly on the AC15.
There is no over heat protection apart from a non resettable thermal fuse within the mains transformer. When that goes due to overheating, it is permanently dead.
The fan is powered from rectified heater supply. If it doesn't run at all it is probably dead, or clogged with dust. The shutdown could be due to one of the internal voltage regulators shutting down from excessive heat, or the microprocessor brain itself shutting down. If the fan isn't working, that will cause too much heat.
My first course of action would be to open it up and clean out any dust that may be inside. I have fixed several PC's with nothing more than a good cleaning.
As previously posted, what happens when it shuts off. Does EVERYTHING go away, or do LED's and tube heaters remain on?
My first course of action would be to open it up and clean out any dust that may be inside. I have fixed several PC's with nothing more than a good cleaning.
As previously posted, what happens when it shuts off. Does EVERYTHING go away, or do LED's and tube heaters remain on?
The fan should run ALL the time. Don't keep toasting the amplifier. Fix the fan before you run it again.
As George says, low-price fans go bad because of dust or cheap oil. Or maybe kids sticking straws in the hole. Open the covers, get a finger on the fan, it should spin freely, maybe with minor "lumps" from the magnets. In old days I would take a stiff fan out, peel the label, work thin oil into the bearing. These days I would tend to copy the size, V, and A off the label, find a new fan.
As George says, low-price fans go bad because of dust or cheap oil. Or maybe kids sticking straws in the hole. Open the covers, get a finger on the fan, it should spin freely, maybe with minor "lumps" from the magnets. In old days I would take a stiff fan out, peel the label, work thin oil into the bearing. These days I would tend to copy the size, V, and A off the label, find a new fan.
I looked at the schematic again out of curiosity and this time I made it to the 4th page where there is some sort of system that can shut down the amplifier. It's wired in between the power receptacle and the power transformer. A relay can control the power in some amps. It appears that the relay driver is connected directly to an output on the microprocessor through a connector labeled "MIDI."
> system that can shut down the amplifier.
Yes. But do we want to second-guess the shut-down system?
The fan should spin all the time. He says it don't. I'd fix that first.
Repeated running to shut-down and quick re-set *could* uncover what burns-up next. I bet the PT is an expensive repair. None of it smells cheap. (Well, maybe inexpensive to the maker, but not to the customer.)
Yes. But do we want to second-guess the shut-down system?
The fan should spin all the time. He says it don't. I'd fix that first.
Repeated running to shut-down and quick re-set *could* uncover what burns-up next. I bet the PT is an expensive repair. None of it smells cheap. (Well, maybe inexpensive to the maker, but not to the customer.)
I totally agree. I just stated what I saw once I got to page 4 since it was said earlier that nothing except a thermal fuse was present.
The convoluted channel switching / muting system is what got my attention since I have been rethinking something similar that I made nearly 30 years ago with a PIC chip and some now extinct National Semiconductor SPI controlled audio chips.
The power switch (ON-OFF-ON) has 2 positions for power on. Position 1 directly connects the mains transformer to supply and position 2 by the power control circuit.
Try in the position 1 and see if the power automatically goes off. If the unit is switched off in position 2, then power control circuit may be the culprit.
Regards,
Mandu.
Try in the position 1 and see if the power automatically goes off. If the unit is switched off in position 2, then power control circuit may be the culprit.
Regards,
Mandu.
Just thinking aloud: I looked at the übercomplicated power on circuit on page 4, top left.
I don´t see a thermal protection switch or similar "safety" or "convenience"
features but a nerdy power switch.
Apparently Power ON toggle has 3 positions:
* Up: ON like on a standard circuit, it connects Mains Live to 1 end of power transformer Primary winding (the other end is always connected to Neutral)
* Center: "intelligent" ON . Called APEM something. (Automatic Power Management???)
Mains goes nowhere through switch but Relay K1 *can* (if so ordered) connect Mains Live to PT Primary.
* Bottom : "Intelligent OFF" (again [rolleyes] smilie)
It sends mains live to an Opto which I *guess* turns K1 relay OFF, no matter what.
My point is that rather than a FAIL condition (which anyway may be possible) I guess somehow the Power ON switching is failing.
Might be any of:
* bad/flaky power switch SW1
* bad/flaky K1 ... which might be as simple as having it poorly plugged in if in a socket, or cracked solder on its pins, or weakened/pitted contacts
* damaged relay drive circuit, built around Q1/Q2/Q3 and associated components OR simply -15V supply might be missing , or +8V line
* OR for some unknown reason Microprocessor might be ordering Q1 to turn K1 OFF
BUT at least as shown, SW1 does have a "straight ON" position, where 2 metallic contacts connect PT primary to Mains, "like in the old days" ... this switch *might* be weak/flaky.
I would check all circuit possibilities, including "direct turn ON" through SW1 , would even bypass it with a regular switch, just vto confirm/discard this possibility ; measure voltage across K1 coil; check whether Q1 gets turned ON by microprocessor (check that it gets around 700mV BE or not).
Just suggesting a few few possible issues to be checked.
And yes, it may be a reaction to a yet unknown prioblem.
Me? ... I am a minimalist, love simple straightforward solutions to problems, even if now and then I have to .... ugh!!! .... think
In general "intelligent devices" trying to "help" me scratch me the wrong way.
NOTE: be careful, part of that circuit is connected to live Mains voltages.
I don´t see a thermal protection switch or similar "safety" or "convenience"
features but a nerdy power switch.Apparently Power ON toggle has 3 positions:
* Up: ON like on a standard circuit, it connects Mains Live to 1 end of power transformer Primary winding (the other end is always connected to Neutral)
* Center: "intelligent"
ON . Called APEM something. (Automatic Power Management???)Mains goes nowhere through switch but Relay K1 *can* (if so ordered) connect Mains Live to PT Primary.
* Bottom : "Intelligent OFF" (again [rolleyes] smilie)
It sends mains live to an Opto which I *guess* turns K1 relay OFF, no matter what.
My point is that rather than a FAIL condition (which anyway may be possible) I guess somehow the Power ON switching is failing.
Might be any of:
* bad/flaky power switch SW1
* bad/flaky K1 ... which might be as simple as having it poorly plugged in if in a socket, or cracked solder on its pins, or weakened/pitted contacts
* damaged relay drive circuit, built around Q1/Q2/Q3 and associated components OR simply -15V supply might be missing , or +8V line
* OR for some unknown reason Microprocessor might be ordering Q1 to turn K1 OFF
BUT at least as shown, SW1 does have a "straight ON" position, where 2 metallic contacts connect PT primary to Mains, "like in the old days" ... this switch *might* be weak/flaky.
I would check all circuit possibilities, including "direct turn ON" through SW1 , would even bypass it with a regular switch, just vto confirm/discard this possibility ; measure voltage across K1 coil; check whether Q1 gets turned ON by microprocessor (check that it gets around 700mV BE or not).
Just suggesting a few few possible issues to be checked.
And yes, it may be a reaction to a yet unknown prioblem.
Me? ... I am a minimalist, love simple straightforward solutions to problems, even if now and then I have to .... ugh!!! .... think
In general "intelligent devices" trying to "help" me scratch me the wrong way.
NOTE: be careful, part of that circuit is connected to live Mains voltages.
Attachments
The supplied schematic shows two versions.
Page 1 is the standard PSU version and page three shows the remote standby PSU version.
Would be useful to find out which one is employed as there will be totally different possibilities.
When fault finding, never get so involved with theory that it confuses you. I see many experienced engineers getting lost. Look at it as a circle. In the centre is the fault. Always, without exception, stay on the outside of the circle.
Keep it simple and methodical.
Fan; yes/no.
Heaters; yes/no.
HT; yes/no.
Low voltage supplies; yes/no.
etc.
It is so easy to fault find that way.
Page 1 is the standard PSU version and page three shows the remote standby PSU version.
Would be useful to find out which one is employed as there will be totally different possibilities.
When fault finding, never get so involved with theory that it confuses you. I see many experienced engineers getting lost. Look at it as a circle. In the centre is the fault. Always, without exception, stay on the outside of the circle.
Keep it simple and methodical.
Fan; yes/no.
Heaters; yes/no.
HT; yes/no.
Low voltage supplies; yes/no.
etc.
It is so easy to fault find that way.
Once you have established that these already listed are not at fault, then and only then, dig a little deeper.Excellent way to find faults in a "normal" amplifier, such as 99.999% of them.
But in this crazy one, a problem in the area I suggest to check will not even feed mains voltage to power transformer so you will find:
even if none of them is at fault
We do not know, we haven't the amplifier on our work benches. We are trying to make constructive comment that should help those with less experience, fault find without having a nervous breakdown.
If one has little experience and is lead into the 'deep end', one will drown.
When the fan stops, it was described as intermittent, check for supplies.
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