You don't say whether the DC voltage you are getting is positive or negative with respect to the polarity of the output.
We need to know that in order to work out which component(s) may be faulty.
Q465 and Q471 (2SD718 and 2SB688 respectively) are the outputs.
If the voltage is positive, then the Q465 and/or its side of the chain are suspect, conversely if it's negative, then Q471 and its side are suspect.
Meter both output transistors anyway to see if either are shorted.
Next you need to meter Q447 and Q453 which are the drivers. They are 2SC2690A and 2SA1220A respectively.
The amplifier stages in this unit are direct coupled (no capacitors in the signal path) so the bias and DC levels of the preceding stages are critical in terms of controlling the output.
We need to know that in order to work out which component(s) may be faulty.
Q465 and Q471 (2SD718 and 2SB688 respectively) are the outputs.
If the voltage is positive, then the Q465 and/or its side of the chain are suspect, conversely if it's negative, then Q471 and its side are suspect.
Meter both output transistors anyway to see if either are shorted.
Next you need to meter Q447 and Q453 which are the drivers. They are 2SC2690A and 2SA1220A respectively.
The amplifier stages in this unit are direct coupled (no capacitors in the signal path) so the bias and DC levels of the preceding stages are critical in terms of controlling the output.
ill check those tomorrow, i traced the circuit to other side of board from what transistors you referred to but ill theck those to be sure all the ones on the side i assumed was subwoofer output section were good
I have double checked the schematic and unless they made some changes to the design at some point, those part locations I gave above refer to the subwoofer amp section.
It shows the speaker output connector, and the sub outputs (+ & -) are on one end of that connector.
Now that we know the output is positive, we can narrow down the offending components a little.
I say a little, because this amp is quite complex in that it uses BTL (bridge-transformerless) output circuitry.
In a normal complementary output stage, the + of the speaker is fed by the output transistors and the - is grounded.
In a BTL situation, the - does not go to ground, it goes to another output stage identical to the first, only difference being the signal fed to it is 180° out of phase to the first stage.
So when the first stage is providing a positive output, the second (or opposing stage) is providing a negative output.
Both stages are identical in terms of parts and their locations. They effectively mirror each other.
The first stage consists of Q446 and Q452 as drivers, and Q464 and Q470 which are the outputs.
The second stage is Q447 and Q453, with Q465 and Q471 as outputs.
This is where it gets a little tricky. In the 'idle' state with no signal applied, both output stages should be sitting at or near zero volts.
Because the output is sitting at 27 volts, it suggests that both output stages are in fact working.
Use your meter and measure between the + speaker terminal and ground, and note that reading, then measure between the - speaker terminal and ground and note that reading. This should help us work out what's going on.
It shows the speaker output connector, and the sub outputs (+ & -) are on one end of that connector.
Now that we know the output is positive, we can narrow down the offending components a little.
I say a little, because this amp is quite complex in that it uses BTL (bridge-transformerless) output circuitry.
In a normal complementary output stage, the + of the speaker is fed by the output transistors and the - is grounded.
In a BTL situation, the - does not go to ground, it goes to another output stage identical to the first, only difference being the signal fed to it is 180° out of phase to the first stage.
So when the first stage is providing a positive output, the second (or opposing stage) is providing a negative output.
Both stages are identical in terms of parts and their locations. They effectively mirror each other.
The first stage consists of Q446 and Q452 as drivers, and Q464 and Q470 which are the outputs.
The second stage is Q447 and Q453, with Q465 and Q471 as outputs.
This is where it gets a little tricky. In the 'idle' state with no signal applied, both output stages should be sitting at or near zero volts.
Because the output is sitting at 27 volts, it suggests that both output stages are in fact working.
Use your meter and measure between the + speaker terminal and ground, and note that reading, then measure between the - speaker terminal and ground and note that reading. This should help us work out what's going on.
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Ah, right - sorry I should have been more specific - I need to know the voltage on each terminal with respect to ground.
Then I can see if the output is swinging high or low, which will hopefully indicate which output stage is crook.
Then I can see if the output is swinging high or low, which will hopefully indicate which output stage is crook.
MRV-F353 Service Manual
Hi, Anyone knows where I can get a service manual for the Alpine MRV-F353 Amp? Thanks
Hi, Anyone knows where I can get a service manual for the Alpine MRV-F353 Amp? Thanks
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