Merry Christmas!!
I have a 7.1 channel Pioneer Elite VSX90 receiver that has a failed output transistor in one of the front channels. This amp uses the obsolete Sanken SAP17 Darlington pair transistors with 5 pins. The P channel device is blown which has internal thermal compensation diodes so I can't really just make my own Darlington pair like I have done before from two discrete transistors.
I only use the two front channels of the receiver and so I do not need all the channels. My question is can I just remove both N and P transistors from a channel I won't be using as donors to install in the bad front channel? My thoughts are as long as I don't connect a load to the channel where I removed the output transistors from nothing bad should happen. With both N and P devices removed there should be no DC present at output to trip protection. So long as there is no load connected the driver transistors shouldn't blow up when signal is present. I may even be able to disable the rear channel that I plan to take the transistors from within the settings of the amp, that way there no signal even goes through that channel that has the output removed.
What concerns me is the feedback loop. I don't have a schematic for the amp so I'm not sure if there is DC feedback that will damage the drivers if the outputs are removed.
What say the experts? Will this work or am I losing my mind?
I have a 7.1 channel Pioneer Elite VSX90 receiver that has a failed output transistor in one of the front channels. This amp uses the obsolete Sanken SAP17 Darlington pair transistors with 5 pins. The P channel device is blown which has internal thermal compensation diodes so I can't really just make my own Darlington pair like I have done before from two discrete transistors.
I only use the two front channels of the receiver and so I do not need all the channels. My question is can I just remove both N and P transistors from a channel I won't be using as donors to install in the bad front channel? My thoughts are as long as I don't connect a load to the channel where I removed the output transistors from nothing bad should happen. With both N and P devices removed there should be no DC present at output to trip protection. So long as there is no load connected the driver transistors shouldn't blow up when signal is present. I may even be able to disable the rear channel that I plan to take the transistors from within the settings of the amp, that way there no signal even goes through that channel that has the output removed.
What concerns me is the feedback loop. I don't have a schematic for the amp so I'm not sure if there is DC feedback that will damage the drivers if the outputs are removed.
What say the experts? Will this work or am I losing my mind?
Without studying a diagram its impossible to say.
No load and no output transistors should mean no current can flow. There may still be a DC offset though if the drivers have a problem and connect to the main output line... in which case pull the drivers as well. If you are not using that channel just remove as much as needed if there should be an offset issue.
No load and no output transistors should mean no current can flow. There may still be a DC offset though if the drivers have a problem and connect to the main output line... in which case pull the drivers as well. If you are not using that channel just remove as much as needed if there should be an offset issue.
That makes perfect sense and confirmed my suspicion that if the drivers do connect directly to the main output line I could still end up with DC at the output.
I think what I will do is try it first with just the outputs removed, if it goes back into protection then the next step is to either remove the drivers or maybe at that point I'll just order a pair of SAP17's from somewhere. Since the devices are obsolete they are hard to find and expensive, even used and pulled transistor pairs are selling for $20 on epay. I'm a cheap bastard and if I can get the amp running without having to spend $10 per transistor I'd be happy since I don't care if all the channels work.
Yes that would be the easiest solution if each channel were on their own board/heatsink assembly but the way they have it setup is 3.5 channels per board/heatsink assembly. They must have done it this way because there is only one set of complimentary pairs per channel. I cannot find the datasheet for the Sanken SP17 but the SP15 is rated for 150 watts. I'm guessing the SP17 is rated for more than 150 watts. The seventh channel has the N channel device one board/heatsink assembly and the complimentary P channel device on the other board/heatsink assembly.
Definitely a strange setup.
So far so good.
I removed only the two SAP17 complimentary pair output transistors for the rear surround as donors for the front channel and after a reset it no longer says "amp error" and doesn't go into protection mode.
I haven't input a signal or hooked it up to speakers. I will button it up and put it in service and hopefully I"m good. I'll report back after that's done.
I removed only the two SAP17 complimentary pair output transistors for the rear surround as donors for the front channel and after a reset it no longer says "amp error" and doesn't go into protection mode.
I haven't input a signal or hooked it up to speakers. I will button it up and put it in service and hopefully I"m good. I'll report back after that's done.
