SX-880 with protection issues
- Thread starter dustmaker
- Start date
dustmaker
Active Member
Yes
dustmaker
Active Member
Reading -0.3…….. I either mis-read or it changed
dustmaker
Active Member
I’m looking at my notes
Reading my notes, this pin was always in the -.3 range before I touched a solder iron to anything
dustmaker
Active Member
merlynski
Curmudgeon Electronicist
The datasheet will tell you which leg is which on the transistors. You can test with your meter or component tester to verify the leads. The schematic and looking at the board artwork drawing (in the SM) and following the traces will tell you if the marking on the PCB is right or wrong. Then you just have to trust yourself to install it correctly. We have all installed components incorrectly, it just goes with the territory. It is a bit harder to deal with when it is vintage equipment with hard to find components.
I could probably come up with a way to mock-up a test or two to simulate some of the functionality. Let me think about this.
Do you have another PA3004?
If you get one of the DIY boards they are repairable. The through-hole one is easier to fix than the SMT one if you do not have SMT reflow capabilities, but . . .
I could probably come up with a way to mock-up a test or two to simulate some of the functionality. Let me think about this.
Do you have another PA3004?
If you get one of the DIY boards they are repairable. The through-hole one is easier to fix than the SMT one if you do not have SMT reflow capabilities, but . . .
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dustmaker
Active Member
Yes, I need to look at the schematic to determine if I am putting transistor correctly. I was relying on the ‘E’ etched into the pcb. Also, I put it in while the unit was on it’s side which always causes me additional conflict when inserting a transistor.
I do not have a replacement PA3004. I was planning on cobbling together your design but I am missing the Zener so this will take a week or so to proceed. In the mean time, I’ll put Q36 and Q37 back in and hopefully do it correctly
dustmaker
Active Member
Ok - I have all my components and t cobbled together a replacement for the PA3004. Because of the issue above, do I run any risk in installing my part? If a transistor or diode is backwards, will it simply not work or could it cause other problems? Also, above you commented that a pcb to replace the PA3004 has the advantage that it an be repaired. How do I know if part of it has failed, how do I test for that?
basically, I look at you schematic and see 4 separate circuits that link to a single connection that connects to a 100k resistor then to pin1. Although I did my best, I’m not 100% certain everything is right. Can I test each of these circuits separately or do I have to hook the entire thing up, put on my safety goggles, ready the fire extinguisher before turning on the 880? Also, should I disconnect Q36 first?
basically, I look at you schematic and see 4 separate circuits that link to a single connection that connects to a 100k resistor then to pin1. Although I did my best, I’m not 100% certain everything is right. Can I test each of these circuits separately or do I have to hook the entire thing up, put on my safety goggles, ready the fire extinguisher before turning on the 880? Also, should I disconnect Q36 first?
merlynski
Curmudgeon Electronicist
Pin 1 on the PA3004 is the power supply input for it. Unless you did something majorly wrong in constructing it I would just put it in place.
Q36 is the pull-up trigger for the overload detectors, pulling does not seem to me to be necessary, nor does leaving it seem risky.
As normal practice, use your DBT when powering up after significant change to your unit. Then check power supply voltages.
If the protection relay clicks after 3 - 6 second you did it right
.
I am not at the computer where the construction details are located.
EDIT: In order to test each section you would need to build test-bed / jigs that are equivalent to your SX-880. So far it has worked fine in every other unit it was tried in.
Q36 is the pull-up trigger for the overload detectors, pulling does not seem to me to be necessary, nor does leaving it seem risky.
As normal practice, use your DBT when powering up after significant change to your unit. Then check power supply voltages.
If the protection relay clicks after 3 - 6 second you did it right
.I am not at the computer where the construction details are located.
EDIT: In order to test each section you would need to build test-bed / jigs that are equivalent to your SX-880. So far it has worked fine in every other unit it was tried in.
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dustmaker
Active Member
Simple question here, is a 100watt bulb ok or should I use a lower wattage bulb when testing significant changes?Pin 1 on the PA3004 is the power supply input for it. Unless you did something majorly wrong in constructing it I would just put it in place.
Q36 is the pull-up trigger for the overload detectors, pulling does not seem to me to be necessary, nor does leaving it seem risky.
As normal practice, use your DBT when powering up after significant change to your unit. Then check power supply voltages.
If the protection relay clicks after 3 - 6 second you did it right
I am not at the computer where the construction details are located.
EDIT: In order to test each section you would need to build test-bed / jigs that are equivalent to your SX-880. So far it has worked fine in every other unit it was tried in.
dustmaker
Active Member
Pin 1 on the PA3004 is the power supply input for it. Unless you did something majorly wrong in constructing it I would just put it in place.
Q36 is the pull-up trigger for the overload detectors, pulling does not seem to me to be necessary, nor does leaving it seem risky.
As normal practice, use your DBT when powering up after significant change to your unit. Then check power supply voltages.
If the protection relay clicks after 3 - 6 second you did it right
I am not at the computer where the construction details are located.
“EDIT: In order to test each section you would need to bu.ild test-bed / jigs that are equivalent to your SX-880. So far it has worked fine in every other unit it was tried in.”
I’m not questioning whether or not your design works. I’m questioning my ability to put all these pieces together in the right orientation without having a formal pcb to follow. If one single component is incorrect, the entire thing may not work and I won’t be able to track down the culprit without either voltages to check or by brute force, rebuilding the entire complete circuit. I guess first things first… hook up what I have and see if it works!
merlynski
Curmudgeon Electronicist
Now I get it! If you build it on a piece of perfboard or similar I might be able to help troubleshoot it, if needed. Give it a shot. After looking at the circuit again, I don't think a construction error would cause a major failure of the rest of the amp, as long as dc offset and bias are within spec before hooking up speakers.
dustmaker
Active Member
Merlynski- an update.
I’ve tried building this part, PA3004, about 8 times and have run into problems each time. Initially, I tried building without a perf board at all, just a bunch of parts soldered and shrink wrapped. Those attempts didn’t work so well. When I thought I had a working bundle, I would end up breaking off a leg on a transistor and essentially having to start over. I tried a couple attempts with perf board that has rails on either side and three holes connected throughout the board, but the board is too big. I tried cutting it down, but the 3 holes connected everywhere caused my design to be too big. I then tried several attempts on a perf board with no copper on it, simply soldering legs together. Seemed to work then it became unwieldy. The last attempt, I put copper foil strips on the blank perf board, with a power rail and a ground rail and in the center, a strip where I would connect the various circuits together from the diodes. I was doing this on a 1” by 1 1/4” board. Started out pretty decent, but then the foil started coming loose is some areas and as I was running out of space, I started adding some taller components. Finally got it together and when I went to install it, I realized I built it backwards and there isn’t enough room for the tall components. Right now I am thinking of starting over and I have a couple questions in your design.
I need to keep this simple in my mind. I’ve been studying the design and this is what I understand. There are 5 separate circuits that connect to the pins 3,4,6,7,8 in addition to a ground pin (pin5) and a power pin (pin1). circuits for pins 4,6 and 7 each have a 4148 diode and they all connect together on the anode side. They also connect to the base of Q7. So all 4 of these then connect to pin 1 (power) through a 100k resistor. If I understand this correctly, there are actually 4 separate circuits and they are only connected together to share the use of a single resistor to power.
Is my understanding correct?
I’ve tried building this part, PA3004, about 8 times and have run into problems each time. Initially, I tried building without a perf board at all, just a bunch of parts soldered and shrink wrapped. Those attempts didn’t work so well. When I thought I had a working bundle, I would end up breaking off a leg on a transistor and essentially having to start over. I tried a couple attempts with perf board that has rails on either side and three holes connected throughout the board, but the board is too big. I tried cutting it down, but the 3 holes connected everywhere caused my design to be too big. I then tried several attempts on a perf board with no copper on it, simply soldering legs together. Seemed to work then it became unwieldy. The last attempt, I put copper foil strips on the blank perf board, with a power rail and a ground rail and in the center, a strip where I would connect the various circuits together from the diodes. I was doing this on a 1” by 1 1/4” board. Started out pretty decent, but then the foil started coming loose is some areas and as I was running out of space, I started adding some taller components. Finally got it together and when I went to install it, I realized I built it backwards and there isn’t enough room for the tall components. Right now I am thinking of starting over and I have a couple questions in your design.
I need to keep this simple in my mind. I’ve been studying the design and this is what I understand. There are 5 separate circuits that connect to the pins 3,4,6,7,8 in addition to a ground pin (pin5) and a power pin (pin1). circuits for pins 4,6 and 7 each have a 4148 diode and they all connect together on the anode side. They also connect to the base of Q7. So all 4 of these then connect to pin 1 (power) through a 100k resistor. If I understand this correctly, there are actually 4 separate circuits and they are only connected together to share the use of a single resistor to power.
Is my understanding correct?
merlynski
Curmudgeon Electronicist
The problems you are running into are why a pro at circuit board layout (not me) made the circuit boards' layout.
Your description seems correct. There are interactive logic functions in this device. And a re-settable timer. The power pin 1 is also an input. They are not readily apparent until you study it in depth. I spent hours studying Pioneer discrete protection circuits, and the logic in them and the PA3004 to come up with the circuit design. Then Alex bread-boarded it, and used his prototyping device and skills to make a final board design. You may find it easier to just acquire a bare board and build it that way. I do not know if he has any left, you could ask him. The information is all there to order more of them if you want/need to, from the same source he used. I put in a request for a quote from a US based PC maker, I have not heard back from them.
EDIT: The only pins that are not 'multi-function/inputs' are ground (5), and the output (3).
Your description seems correct. There are interactive logic functions in this device. And a re-settable timer. The power pin 1 is also an input. They are not readily apparent until you study it in depth. I spent hours studying Pioneer discrete protection circuits, and the logic in them and the PA3004 to come up with the circuit design. Then Alex bread-boarded it, and used his prototyping device and skills to make a final board design. You may find it easier to just acquire a bare board and build it that way. I do not know if he has any left, you could ask him. The information is all there to order more of them if you want/need to, from the same source he used. I put in a request for a quote from a US based PC maker, I have not heard back from them.
EDIT: The only pins that are not 'multi-function/inputs' are ground (5), and the output (3).
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