Miniwatt N3 not turning on!

vkengeri · 12:55 AM

Hi, I have a 2year old Miniwatt N3 that had been working quite well but just stopped working. I thought it was the fuse but the light on the switch would not work with out the fuse working. I removed the fuse and checked it and seems like it did not blow. Any one have thoughts on what may be wrong? Thanks.

- vkengeri

ballpencil · 11th February 2014, 07:25 AM

First, do the tubes light up, meaning that the heater works?
Can you trace voltages? The pins on the tube looks accessible to voltmeter probes without unplugging them. We need to understand how good you understand electronics before proceeding.

azazello · 11th February 2014, 07:26 AM

Is main transformer common for both channels? Are tubes light?
1. You can measure with voltmeter /in AC mode of voltmeter/ is there AC on taps of transformer - high and 6.3 v/...Is there DC +U /in DC mode/ after bridge rectifier. Maybe something is wrong in PSU?
Please, give us results. Next measuring advice - after first.

vkengeri · 11th February 2014, 04:04 PM

The tubes are not lighting up or getting hot. I am not sure what I need to open to measure the voltages but will give it a try by opening the tops of the two transformers.

azazello · 11th February 2014, 09:33 PM

I can't see power transformer. Maybe +U DC and 6.3 V AC are formed direct from AC net? IMO, it's dangerous and don't open amplifier, if it is connected to the wall. Maybe something is wrong with 6.3 former and/or power diode rectifier.
IMO, You can ask some person, who understand electronic and SS rectifiers.

lexx21 · 11th February 2014, 09:41 PM

Simplistic suggestion, though very valid.... fuses? Check the fuse with an ohm meter (not in the circuit of course)

azazello · 10:17 PM

miniwatt N3 | ???????????? - ?????
There is inside picture.....it seems something like HF impulse PS, maybe problem is here....with IC on Allum. cooler plate.

yagoolar · 11th February 2014, 10:10 PM

You mean SMPS. Thats odd...

ballpencil · 12th February 2014, 12:27 AM

Tubes not lighting up means there's no heater power supply. Now the problem is whether the plates are not getting power as well. Looking at the internal pic, I think plates are supplied directly from a rectified mains while heaters gets a stepdown transformer? So.. first thing i would do is to unplug all the tubes and check if there's supply for the plates. If plates are powered, then it could be the step down transformer for the heater.

ishiru · 12th February 2014, 08:26 AM

it's SMPS supply.that's why the mains was directly rectified.(i assume SMPS used for smaller case and lighter weight

)

10th February 2014, 11:36 PM	#1
vkengeri diyAudio Member Join Date: Feb 2014	Miniwatt N3 not turning on! Hi, I have a 2year old Miniwatt N3 that had been working quite well but just stopped working. I thought it was the fuse but the light on the switch would not work with out the fuse working. I removed the fuse and checked it and seems like it did not blow. Any one have thoughts on what may be wrong? Thanks. - vkengeri Last edited by vkengeri; 11th February 2014 at 12:55 AM.

11th February 2014, 07:26 AM	#3
azazello diyAudio Member Join Date: Aug 2008 Location: USA	Is main transformer common for both channels? Are tubes light? 1. You can measure with voltmeter /in AC mode of voltmeter/ is there AC on taps of transformer - high and 6.3 v/...Is there DC +U /in DC mode/ after bridge rectifier. Maybe something is wrong in PSU? Please, give us results. Next measuring advice - after first. __________________ Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

11th February 2014, 09:33 PM	#5
azazello diyAudio Member Join Date: Aug 2008 Location: USA	I can't see power transformer. Maybe +U DC and 6.3 V AC are formed direct from AC net? IMO, it's dangerous and don't open amplifier, if it is connected to the wall. Maybe something is wrong with 6.3 former and/or power diode rectifier. IMO, You can ask some person, who understand electronic and SS rectifiers. __________________ Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,...

11th February 2014, 10:05 PM	#7
azazello diyAudio Member Join Date: Aug 2008 Location: USA	miniwatt N3 \| ???????????? - ????? There is inside picture.....it seems something like HF impulse PS, maybe problem is here....with IC on Allum. cooler plate. __________________ Projects: SE GK71, SE 12BQ6, PP KT88, OTL-OCL 6AS7 Gen. Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, E84L Siemens, E236L Telefunken, headphone ampl. OTL Loftin White 6AS7 RCA,... Last edited by azazello; 11th February 2014 at 10:17 PM.

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11th February 2014, 07:25 AM	#2
ballpencil diyAudio Member Join Date: Nov 2013	First, do the tubes light up, meaning that the heater works? Can you trace voltages? The pins on the tube looks accessible to voltmeter probes without unplugging them. We need to understand how good you understand electronics before proceeding.

11th February 2014, 04:04 PM	#4
vkengeri diyAudio Member Join Date: Feb 2014	The tubes are not lighting up or getting hot. I am not sure what I need to open to measure the voltages but will give it a try by opening the tops of the two transformers.

11th February 2014, 09:41 PM	#6
lexx21 diyAudio Member Join Date: Mar 2011 Location: North Carolina	Simplistic suggestion, though very valid.... fuses? Check the fuse with an ohm meter (not in the circuit of course)

11th February 2014, 10:10 PM	#8
yagoolar diyAudio Member Join Date: Oct 2004 Location: Warsaw, PL	You mean SMPS. Thats odd...

12th February 2014, 12:27 AM	#9
ballpencil diyAudio Member Join Date: Nov 2013	Tubes not lighting up means there's no heater power supply. Now the problem is whether the plates are not getting power as well. Looking at the internal pic, I think plates are supplied directly from a rectified mains while heaters gets a stepdown transformer? So.. first thing i would do is to unplug all the tubes and check if there's supply for the plates. If plates are powered, then it could be the step down transformer for the heater.

12th February 2014, 08:26 AM	#10
ishiru diyAudio Member Join Date: Oct 2013 Location: Jakarta, ID - Nagasaki, JP	it's SMPS supply.that's why the mains was directly rectified.(i assume SMPS used for smaller case and lighter weight )

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