output devices installed before testing?

KCC · 13th February 2004, 04:00 PM

Hi,
I am trying to work on my Yamaha M2 which one side is not working.I've replaced some fuse resistors and transistors and,yes,all the output transistors are fried. At $25 a peice I am somewhat hesitate to install the new ones before fire it up. At this point the voltage reading is incorrect as compare to what's provided in the schematics. Anyone has experiences in these situation please give me some ideas as to what to do.Thanks in advance.

Peter

dmfraser · 13th February 2004, 04:25 PM

The usual. Before you fire it up, connect it with a 100W lamp in series with the AC line. It will still work at low volume but if there are further faults, the lamp will prevent you from blowing the outputs.

KCC · 13th February 2004, 06:06 PM

Ok,Dan,I don't quite get what you mean.You mean connect the amp to a 100w light bulb in series and the light bulb to ac line.Right? If so,in what way the output devices are protected?

Peter

maylar · 13th February 2004, 07:45 PM

The light bulb acts as a current limit on the AC mains. Low resistance when cold (amplifier idling OK), high resistance when hot (amplifier drawing too much current). The more current your circuit tries to draw, the more the light bulb limits it.

Personally, I use a Variac.

millwood · 13th February 2004, 11:17 PM

I usually install a 10ohm 10w resistor in each rail just to be save. After making sure that the front stage works well, I then take the resistor on the emitter of output stage. You will still hear sound (of reasonably good quality). From there, I go down to 4.7ohm, and 1ohm.

It is NOT 100% fool proof but did save me more than a few times.

Tube_Dude · 13th February 2004, 11:35 PM

I usually use a variable Dual Rail Dc power supply...begining from 0 volts, i increase slowly the voltage looking at the current draw...if everything is ok...i connect the mains.

KCC · 17th February 2004, 01:59 AM

I finally installed the output devices and using the variac slowly bring up the power. The right channel does show problems as rail voltages show up in all three legs of all transistors in the driver board. This is the same situation prior to the installation of the output devices.I might have to test each and every components in the driver board.There are not that many of them anyways.

13th February 2004, 04:00 PM	#1
KCC diyAudio Member Join Date: Mar 2002 Location: Edmonton	output devices installed before testing? Hi, I am trying to work on my Yamaha M2 which one side is not working.I've replaced some fuse resistors and transistors and,yes,all the output transistors are fried. At $25 a peice I am somewhat hesitate to install the new ones before fire it up. At this point the voltage reading is incorrect as compare to what's provided in the schematics. Anyone has experiences in these situation please give me some ideas as to what to do.Thanks in advance. Peter

13th February 2004, 04:25 PM	#2
dmfraser diyAudio Member Join Date: Dec 2003 Location: Orange County, CA	Amp testing The usual. Before you fire it up, connect it with a 100W lamp in series with the AC line. It will still work at low volume but if there are further faults, the lamp will prevent you from blowing the outputs. __________________ Dan Fraser

13th February 2004, 07:45 PM	#4
maylar diyAudio Member Join Date: Jun 2003 Location: Connecticut	The light bulb acts as a current limit on the AC mains. Low resistance when cold (amplifier idling OK), high resistance when hot (amplifier drawing too much current). The more current your circuit tries to draw, the more the light bulb limits it. Personally, I use a Variac. __________________ dave

13th February 2004, 11:35 PM	#6
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	The final countdown... I usually use a variable Dual Rail Dc power supply...begining from 0 volts, i increase slowly the voltage looking at the current draw...if everything is ok...i connect the mains. __________________ Jorge

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13th February 2004, 06:06 PM	#3
KCC diyAudio Member Join Date: Mar 2002 Location: Edmonton	Ok,Dan,I don't quite get what you mean.You mean connect the amp to a 100w light bulb in series and the light bulb to ac line.Right? If so,in what way the output devices are protected? Peter

13th February 2004, 11:17 PM	#5
millwood Account Disabled Join Date: Apr 2003 Location: US	I usually install a 10ohm 10w resistor in each rail just to be save. After making sure that the front stage works well, I then take the resistor on the emitter of output stage. You will still hear sound (of reasonably good quality). From there, I go down to 4.7ohm, and 1ohm. It is NOT 100% fool proof but did save me more than a few times.

17th February 2004, 01:59 AM	#7
KCC diyAudio Member Join Date: Mar 2002 Location: Edmonton	I finally installed the output devices and using the variac slowly bring up the power. The right channel does show problems as rail voltages show up in all three legs of all transistors in the driver board. This is the same situation prior to the installation of the output devices.I might have to test each and every components in the driver board.There are not that many of them anyways.

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