| Omegasteffy |
Hi, im am trying to repair an older Pioneer surround amplifier (VSA-805S) and are in need of a schematic. I would be happy if anyone were able to email it or link to it.
The problem is that the Left channel does not work if it is loaded and a signal is applied. If i connect a speaker the amplifier will report "Overload" and enter standby mode, once i turn the volume knob.
I tried to measure voltage at the Collector of the NPN output transistor and the at the driver. Here the supply drop from 47 V to 44.3 V before the amplifier report overload.
The power amplifiers are mounted on a pair of prints which are sperated from the remaining amplifier (signal processing, control and PSU). There is a overload line from the power amplifier which seems to be digitally controlled. A negative pulse occur on the overload line before the amplifier goes into standby.
I think it could ease the the repair a lot if anyone had a schematic or a service manual.
PS. On the amplifier modules there are made room for an extra output transistors and i guess that the same modules might are used for larger surround amplifiers from the same year 1996. I am not aware of which models this might be. |
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| Leolabs |
| Try to check for shorted semiconductors and dry sloder joints. |
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| Omegasteffy |
I will try to resolder any doubtful solderings.
Yesterday i found a bad connection on the emitter resistor of the left channels power transistor. It is a shared power resistor and i resoldered all three pins. Thereby forgot to note whether it was the positive or negative part where the connection was gone loose. |
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| Omegasteffy |
Uff! It seems i might have found the flaw. It tried testing with a variable power resistor and it did not seem like it got overloaded until i went down to approx 2 ohm. I tried swiching speakers and now it seems to output sinus tones just fine. I guees i fried the speaker before i found the bad emitter resistor connection or maybee the speaker was already fried. So i think have spent a few days wondering why the amplifier did not work with this speaker, when the problem actually was the speaker :rolleyes:.
I will bring it home from the lab and test with music and other speakers. |
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