Amplifier repair
Guest
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Not really interested in having someone else fix the amp, I bought it for a learning project. If I can't get it up and running, no big deal...
There must be a way to test the powersupply?
[ March 01, 2004, 10:22 AM: Message edited by: Kilowatt ]
There must be a way to test the powersupply?
[ March 01, 2004, 10:22 AM: Message edited by: Kilowatt ]
Guest
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Here's what I dont understand about the amp...
I can see the 44VDC being passed on to the out put terminals through a shorted fet, but what would cause it to cycle on for 3 seconds (44VDC), then drop to 0V for 1 second, and back up to 44VDC in a cycle (with no input)? When it drops to 0V the power LED dims, and shuts off the right channel as well as far as I can tell. There must be another short, but why only every 3 seconds?
Hmmm...I'll have to take some more measurements in the power supply...
I can see the 44VDC being passed on to the out put terminals through a shorted fet, but what would cause it to cycle on for 3 seconds (44VDC), then drop to 0V for 1 second, and back up to 44VDC in a cycle (with no input)? When it drops to 0V the power LED dims, and shuts off the right channel as well as far as I can tell. There must be another short, but why only every 3 seconds?
Hmmm...I'll have to take some more measurements in the power supply...
Guest
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OK, I tested the amp again with the blown fets on the left channel removed to see if the right channel would work. Well I now have a weak output on both channels which is heavily distorted (no more 44VDC). The distortion on the left channel is most likely due to the missing fets I would imagine, but should the right channel be distorted as well?
1000 Watt CAFz'r
Joined: Aug 2001
Posts: 1,770
if you have removed all the transistors from the channel you should have no sound from that channel
that would indicate you still have transistors on that channel
p.s. if you have no input signal there should be no voltage at the speaker terminals
and voltage there indicates you still have damaged parts at that channel
that would indicate you still have transistors on that channel
p.s. if you have no input signal there should be no voltage at the speaker terminals
and voltage there indicates you still have damaged parts at that channel
Guest
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I removed 4 of the 8 from the left channel, so yes there were fets still on the board.
When I had no signal input into the amp, I read no Voltage on the output.
When I had a signal fed into the amp, the output was weak and distorted on both channels. I thought the right channel may still work?
When I had no signal input into the amp, I read no Voltage on the output.
When I had a signal fed into the amp, the output was weak and distorted on both channels. I thought the right channel may still work?
Guest
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mister steve-an amplifier adds DC to the incomming AC signal which results in an amplified AC signal.
My particular amplifier's output stage transistors (which add the DC to AC signal) are shorted dumping the full DC signal from the power supply on the output terminals. If I have no AC signal into the amp, I will have no AC signal comming out of the amp.
I am not measuring sound here, because the amplifier wont even amplify in its current state.
My particular amplifier's output stage transistors (which add the DC to AC signal) are shorted dumping the full DC signal from the power supply on the output terminals. If I have no AC signal into the amp, I will have no AC signal comming out of the amp.
I am not measuring sound here, because the amplifier wont even amplify in its current state.
1000 Watt CAFz'r
Joined: Aug 2001
Posts: 1,770
the transistors have dc as a power supply
when a input signal is applied to the transistor the transistor switches the dc into the same waveform the the input signal is
except its a larger output
when your output transistors fry then usually the dc that is the power supply for your outputs gets sent directly to your speaker outputs
because usually when they fry the transistor shorts out
when a input signal is applied to the transistor the transistor switches the dc into the same waveform the the input signal is
except its a larger output
when your output transistors fry then usually the dc that is the power supply for your outputs gets sent directly to your speaker outputs
because usually when they fry the transistor shorts out
50 Watt CAFz'r
Joined: Feb 2004
Posts: 295
so in other words at your speaker terminals you should not be reading 44v dc but a nice number in ac, your meter will read dc from an ac sorce but will get all goofy about it.
like you said, it wont amplify at the moment, you still have blown stuff, best way to cheak is to look for burnt stuff, grab your meter and measure continuity acrosse everything in the path, a skimatic of the amp helps at this point
that and your amp is ment to drive something, it dosent work to well if you just plug a meter into speaker outs and turn it on.
connect a speaker and use an amp meter, use ohms law to figure voltage in this case.
also you said you have s scope?
plug it in and play a test tone, see what the wave looks like.
and i aplogise if i sound preachy
[ March 02, 2004, 06:32 PM: Message edited by: mister steve ]
like you said, it wont amplify at the moment, you still have blown stuff, best way to cheak is to look for burnt stuff, grab your meter and measure continuity acrosse everything in the path, a skimatic of the amp helps at this point
that and your amp is ment to drive something, it dosent work to well if you just plug a meter into speaker outs and turn it on.
connect a speaker and use an amp meter, use ohms law to figure voltage in this case.
also you said you have s scope?
plug it in and play a test tone, see what the wave looks like.
and i aplogise if i sound preachy
[ March 02, 2004, 06:32 PM: Message edited by: mister steve ]
