SX-780 Issues / PA3004?
- Thread starter Mike Scaggs
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- no relay click pa3004 sx-780
Your Q22 isn't behaving.
Remove Q22 and do/post a six way test on it.
also remove Q20 and do/post a six way test on it.
also do/post a six way test on the ksa940 that you used to have in Q20.
do you have new transistors (of these types)?
Remove Q22 and do/post a six way test on it.
also remove Q20 and do/post a six way test on it.
also do/post a six way test on the ksa940 that you used to have in Q20.
do you have new transistors (of these types)?
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Mike Scaggs
New Member
merlynski
Curmudgeon Electronicist
"Brand New" components can be bad.
What are the results of a six-way test on the new transistor?
If the flat side of the transistor is facing the camera you have mis-identified the leads on the transistor.
From the video (if I am seeing correctly) you have the meter leads on the emitter and collector. A good KSA1013 will show open for either polarity between emitter and collector.
ALWAYS check the datasheet for lead configuration, it varies, sometimes between slightly different versions of the same transistor.
What are the results of a six-way test on the new transistor?
If the flat side of the transistor is facing the camera you have mis-identified the leads on the transistor.
From the video (if I am seeing correctly) you have the meter leads on the emitter and collector. A good KSA1013 will show open for either polarity between emitter and collector.
ALWAYS check the datasheet for lead configuration, it varies, sometimes between slightly different versions of the same transistor.
Mike Scaggs
New Member
merlynski
Curmudgeon Electronicist
The KSA1013 is a PNP transistor, to forward bias the junctions you have to have the negative (black) lead on the Base. With the red lead on the base you will get an OL reading because it cannot conduct.
Study this link about six way testing the two different transistor polarities (NPN and PNP): Bipolar Junction Transistor Testing Basics | Audiokarma Home Audio Stereo Discussion Forums
The way I learned (long ago) Was the PNP has the Pointing iN Pointer, NPN has the Not Pointing iN pointer. The N lead has to have the negative lead connected to forward bias it.
The other thing about the six way test, if it tests bad it is bad, if it does not test bad, it may still be bad. They six way test weeds out bad transistors, but does NOT certify it is good.
Study this link about six way testing the two different transistor polarities (NPN and PNP): Bipolar Junction Transistor Testing Basics | Audiokarma Home Audio Stereo Discussion Forums
The way I learned (long ago) Was the PNP has the Pointing iN Pointer, NPN has the Not Pointing iN pointer. The N lead has to have the negative lead connected to forward bias it.
The other thing about the six way test, if it tests bad it is bad, if it does not test bad, it may still be bad. They six way test weeds out bad transistors, but does NOT certify it is good.
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Mike Scaggs
New Member
merlynski
Curmudgeon Electronicist
You are welcome!
So the old one does not fail the test, and the new one appears good. The ultimate test is to install the new ones and test the power supply voltages.
NOTE: Transistors in power (supply or amp) circuits that are directly connected to each other, very often kill each other when one in the circuit fails. If you just replace one, the other failed (or damaged) one will take out the new one as well. They way to get past that is to replace all the direct connected semiconductors at one time.
So, to fix the -39.5vdc regulator, replace Q22 and Q20 at the same time without powering up between parts installation.
ALSO, Q24, the FET (Field Effect Transistor) rarely fails in these type circuits. FETs are easily damaged by static electricity when they are not installed in a PCB, so removing it to test it can damage it just by handling, it while it is uninstalled. The 2SK34 (Q24) is unobtainium, long out of production. There are ways to mitigate the risk by having a static conductive mat and a wrist strap. If you do not get the regulator working, and all other components are good, there is another type component that can be installed in place of Q24, but it is usually not necessary.
So the old one does not fail the test, and the new one appears good. The ultimate test is to install the new ones and test the power supply voltages.
NOTE: Transistors in power (supply or amp) circuits that are directly connected to each other, very often kill each other when one in the circuit fails. If you just replace one, the other failed (or damaged) one will take out the new one as well. They way to get past that is to replace all the direct connected semiconductors at one time.
So, to fix the -39.5vdc regulator, replace Q22 and Q20 at the same time without powering up between parts installation.
ALSO, Q24, the FET (Field Effect Transistor) rarely fails in these type circuits. FETs are easily damaged by static electricity when they are not installed in a PCB, so removing it to test it can damage it just by handling, it while it is uninstalled. The 2SK34 (Q24) is unobtainium, long out of production. There are ways to mitigate the risk by having a static conductive mat and a wrist strap. If you do not get the regulator working, and all other components are good, there is another type component that can be installed in place of Q24, but it is usually not necessary.
Mike Scaggs
New Member
Thank you for all the great advice and info. I plan to work on this this evening after work and see if I can get her going. I do have a new Q20,Q22 on hand. I will report my finding soon thereafter.
~mike
Mike Scaggs
New Member
merlynski
Curmudgeon Electronicist
Looks like you have Q22 installed incorrectly (flipped 180°), its emitter should be 0vdc (connected to the ground trace), its base about -0.6vdc and the collector about -40vdc.
The lead order of the KSA1013 is ECB, the lead order of the original 2SA904 is BCE, so the replacement Q22 will have the flat side facing the opposite direction from the original one, when correctly installed.
What is the 904 for Q20? Did you mean KSA940??
Q22 correct alignment:
The lead order of the KSA1013 is ECB, the lead order of the original 2SA904 is BCE, so the replacement Q22 will have the flat side facing the opposite direction from the original one, when correctly installed.
What is the 904 for Q20? Did you mean KSA940??
Q22 correct alignment:
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Mike Scaggs
New Member
She looks right to me??
Mike Scaggs
New Member
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merlynski
Curmudgeon Electronicist
She looks right to me??
That does look correct, then your drawing in post #31 is mismarked.
Are you measuring and writing down what you are seeing from this annotated picture of yours?
Did you take a picture of the original configuration, before any parts were changed?
Mike Scaggs
New Member
I did take pictures and you are right that the 1013 needs to be flipped. I missed that on the instructions. I put my last new one in and now it reads voltages that I listed. Now I am wondering if I blew up the B536/A940 when I put Q22 in wrong..errrrr. Should be simple but here I am. Thanks again for sticking it out with me.
merlynski
Curmudgeon Electronicist
You are welcome! Sometimes remote troubleshooting can be very frustrating, for both ends of the conversation. 
Do you have a KSA992F? I would use that instead of the KSA1013, if you have one, or need to order more parts. (512-KSA992FBTA, Mouser).
What other small PNP transistors do you have on hand? Maybe we can figure out another substitution . . .
I never trust transistors that have been installed incorrectly, I replace them.
Replace Q22 and Q20 with new, at the same time (installed correctly) and see what happens.
I have not given up on anybody yet . . . so we will keep going if you are still willing.
FWIW, I buy small transistors in 100 lots, to get the price break, and for when I do the same things you are doing (we all have at one time or another).
Do you have a KSA992F? I would use that instead of the KSA1013, if you have one, or need to order more parts. (512-KSA992FBTA, Mouser).
What other small PNP transistors do you have on hand? Maybe we can figure out another substitution . . .
I never trust transistors that have been installed incorrectly, I replace them.
Replace Q22 and Q20 with new, at the same time (installed correctly) and see what happens.
I have not given up on anybody yet . . . so we will keep going if you are still willing.
FWIW, I buy small transistors in 100 lots, to get the price break, and for when I do the same things you are doing (we all have at one time or another).
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Mike Scaggs
New Member
Yeah, I'm going to need to order some stuff I'm afraid. Tube stuff I have lots of, but this (new to me) SS stuff, all I might have in my stock is resistors and such.You are welcome! Sometimes remote troubleshooting can be very frustrating, for both ends of the conversation.
Do you have a KSA992F? I would use that instead of the KSA1013, if you have one, or need to order more parts. (512-KSA992FBTA, Mouser).
What other small PNP transistors do you have on hand? Maybe we can figure out another substitution . . .
I never trust transistors that have been installed incorrectly, I replace them.
Replace Q22 and Q20 with new, at the same time (installed correctly) and see what happens.
I have not given up on anybody yet . . . so we will keep going if you are still willing.
FWIW, I buy small transistors in 100 lots, to get the price break, and for when I do the same things you are doing (we all have at one time or another).