Output transistors keep blowing on SX-2500

I still have a LOT to learn!
I did notice that node Pin 4 was not connected (graphically) to the Output side of the output capacitor, which is half of the negative feedback path, through the two 15kΩ resistors. Was that deliberate or an oops?

That's an oops. :oops:
 
It looks like some cool conversation happened while I was gone. It's been busy on my end here lately. My bench has been consumed with paying work, and I had to go to the auction for my wife's store yesterday, so the pioneer had to move to the side. Got to pick up a traffic light for myself at the auction though. I figured it would look pretty cool in the display room at my shop. The problem is, I need to cobble together a controller to make it flash to music tomorrow during an event all the businesses are having in the downtown area. Building it, programming it, and getting it wired to go is likely going to take me the rest of the night.

Sometimes I wish I could just find one or two things fun and interesting in life. Now I have traffic lights to fiddle with too. Doing something like this might be too tempting:
open-sex.jpg
 
It looks like some cool conversation happened while I was gone. It's been busy on my end here lately. My bench has been consumed with paying work, and I had to go to the auction for my wife's store yesterday, so the pioneer had to move to the side. Got to pick up a traffic light for myself at the auction though. I figured it would look pretty cool in the display room at my shop. The problem is, I need to cobble together a controller to make it flash to music tomorrow during an event all the businesses are having in the downtown area. Building it, programming it, and getting it wired to go is likely going to take me the rest of the night.

Sometimes I wish I could just find one or two things fun and interesting in life. Now I have traffic lights to fiddle with too. Doing something like this might be too tempting:
View attachment 1349934
Yeah, I hate it when life gets in the way of AK. :rolleyes: :jump:
 
I may have found something we have been missing. There is a connection between the Main In jacks and the Main Amp Unit that is very difficult to see on the large interconnect schematic, of which there is more than one version, some that do not have it. The audio path loops through the Protector Unit AWM-004, which has a mute circuit on it that is not present in all the SMs that I have seen. From what PoDuck said in an earlier post I believe these match his unit:
SX-2500partial.png AWM-004.png
The connections are squeezed into the schematic to the left of the Main Amp, intermixed with the switch contacts, and just above the Protector Unit. I have added some color splotches to make it easier to see. They are labeled W, X, Z, and Y.
 
Good catch. Service manual and schematics I have do not have that protect circuit. Mine has board number W18-29 for the protector unit, which is a simpler circuit than the AWM-004. I'm wondering if my schematics are an earlier version of the SX-2500? The W18-29 is missing those W, X, Y, Z connections.
 
The muting FETs on the protector board at isolated by caps, so you could jumper in and out on the board to by-pass it. (7 to 10 and 11 to14)
 
The schematics I have show that module in the main interconnect diagram, but they don't have the schematic for that board. My question is how would that board be reducing the power on a single channel, and not cutting it out altogether? I'll bypass that board and see what happens though.

I'll be getting back to work on that a little later today. I have to clean up my bench from all the other crap I've had on it since I last worked on the Pioneer. I really need a better way of organizing things around here.

Unfortunately, I've been told I am required to go watch some chick flick tonight, so I won't be able to work on it late. At least I'll get a nap in.
 
The schematics I have show that module in the main interconnect diagram, but they don't have the schematic for that board. My question is how would that board be reducing the power on a single channel, and not cutting it out altogether? I'll bypass that board and see what happens though.

I'll be getting back to work on that a little later today. I have to clean up my bench from all the other crap I've had on it since I last worked on the Pioneer. I really need a better way of organizing things around here.

Unfortunately, I've been told I am required to go watch some chick flick tonight, so I won't be able to work on it late. At least I'll get a nap in.

If one of the jFETs was bad that one channel could be affected, but not the other. Both channels go through on separate paths, but both jfets are controlled by the same transistor, Q5..
 
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For those who use LTspice here is a zipped .asc with the Main Amp from @LesE and an added partial AWM-004 Protect circuit with a 1 second protect event.
 

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  • sx-2500 W23-004 wProt Main Amp Unit.zip
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The schematics I have show that module in the main interconnect diagram, but they don't have the schematic for that board. My question is how would that board be reducing the power on a single channel, and not cutting it out altogether? I'll bypass that board and see what happens though.

I'll be getting back to work on that a little later today. I have to clean up my bench from all the other crap I've had on it since I last worked on the Pioneer. I really need a better way of organizing things around here.

Unfortunately, I've been told I am required to go watch some chick flick tonight, so I won't be able to work on it late. At least I'll get a nap in.
did you fix sx2500
 
I am sorry I didn't update this at the time. I actually got this problem fixed. The problem appears to have been a cold solder joint. I am not sure what was not making a connection since I didn't find it formulaicly, nor did my eyes pick up on it. I just got so frustrated that I went over the entire amplifier board and added solder to each joint, on the off chance it was a missed cold solder joint. When I next tested things, it worked.

Thanks everyone for the help.
 
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