TOA W906-A amp blows fuses

ajm14120 · 12th October 2007, 08:47 PM

I need some help with a TOA W906-A amplifier as it keeps blowing the 3amp fast blow fuse. It is rated at 60w RMS and 100w peak. It's an old amp at my school and we are trying to get it up and working again. I think that there is a short somewhere on the boards, it looks like a complicated set up as there is an Eq and everything, I need help narrowing what boards would have the fault, any suspect components. I have the service manual and the part numbers I just need some help on finding the faulty components. If I put in a new fuse the amp turns on with no load attached, then blows about 5 seconds later when the amp engages. The manuals are attached, if they are any help.

Netlist · 12th October 2007, 08:51 PM

Quote:

Originally posted by ajm14120
The manuals are attached, if they are any help.

Please try again, I'll gladly have a look.
Let me know if you have trouble posting them.

/Hugo

ajm14120 · 12th October 2007, 10:24 PM

I guess the file is too big, here is a link
http://files-upload.com/files/557657/service manual.pdf

Netlist · 13th October 2007, 06:16 AM

First, disconnect the mains transformer from the Module Power Supply PCB and Condenser PCB to rule out the transformer.
If the fuses still pops, you don't need to look any further.
If it doesn't, measure the bridge rectifier D901 and suspect the capacitors on the Condenser PCB.
If these are fine, proceed with the output transistors Q901, Q902.

/Hugo

Original Burnedfingers · 13th October 2007, 10:42 PM

Use a light bulb in series with an AC cord to feed it power or use a variac.

Its been a while since I seen one but I believe the power amplifier portion can be separated via connectors to allow checking of the mix and EQ sections. If they come up and run ok then the problem is in the power amplifier module. If I remember correctly there is an op amp (8 pin dip) that can go bad when you overdrive the amp and cause it to take the fuse. Somewhere around my shop is a service manual and if I can find it maybe I can be of more help.

This is one of Toa's models of lesser value. Its meant to be a 60 watt amplifier with zero headroom. Don't count on 100 watt peaks
because this is one amp that will lunch if you try it.

This probably belongs in the solid state forum because it is not a chip amp but a in wall oscillator.

Original Burnedfingers · 15th October 2007, 10:29 AM

This surely doesn't belong in the chip amp section because it is a commercial piece without chip amps.

12th October 2007, 08:47 PM	#1
ajm14120 diyAudio Member Join Date: Oct 2007	TOA W906-A amp blows fuses I need some help with a TOA W906-A amplifier as it keeps blowing the 3amp fast blow fuse. It is rated at 60w RMS and 100w peak. It's an old amp at my school and we are trying to get it up and working again. I think that there is a short somewhere on the boards, it looks like a complicated set up as there is an Eq and everything, I need help narrowing what boards would have the fault, any suspect components. I have the service manual and the part numbers I just need some help on finding the faulty components. If I put in a new fuse the amp turns on with no load attached, then blows about 5 seconds later when the amp engages. The manuals are attached, if they are any help.

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12th October 2007, 10:24 PM	#3
ajm14120 diyAudio Member Join Date: Oct 2007	I guess the file is too big, here is a link http://files-upload.com/files/557657/service manual.pdf

13th October 2007, 06:16 AM	#4
Netlist diyAudio Moderator Emeritus Join Date: Jan 2003	First, disconnect the mains transformer from the Module Power Supply PCB and Condenser PCB to rule out the transformer. If the fuses still pops, you don't need to look any further. If it doesn't, measure the bridge rectifier D901 and suspect the capacitors on the Condenser PCB. If these are fine, proceed with the output transistors Q901, Q902. /Hugo

13th October 2007, 10:42 PM	#5
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Use a light bulb in series with an AC cord to feed it power or use a variac. Its been a while since I seen one but I believe the power amplifier portion can be separated via connectors to allow checking of the mix and EQ sections. If they come up and run ok then the problem is in the power amplifier module. If I remember correctly there is an op amp (8 pin dip) that can go bad when you overdrive the amp and cause it to take the fuse. Somewhere around my shop is a service manual and if I can find it maybe I can be of more help. This is one of Toa's models of lesser value. Its meant to be a 60 watt amplifier with zero headroom. Don't count on 100 watt peaks because this is one amp that will lunch if you try it. This probably belongs in the solid state forum because it is not a chip amp but a in wall oscillator.

15th October 2007, 10:29 AM	#6
Original Burnedfingers diyAudio Member Join Date: Nov 2002	This surely doesn't belong in the chip amp section because it is a commercial piece without chip amps.