Pioneer SX-980 Protection Relay Kicking Out

FWIW, grounding the PA3004 pin 4 (this is overload and dc offset detection, yes?) did not stop the cycling, also he said earlier he has replaced Q1. He also said he had replaced all the caps on the prot board.
 
Check FU6, or test short it or just replace it for now.

If it is old age failing, fu5 could carry the 13v dc load alone or smooth over the intermittent, showing up ONLY at the AC 20v output of the power supply.
 
FACT #1, when the protect circuit is reacting on and off FASTER than the timing interval, it's the relay DRIVE part of the circuit.
Which is WHY I asked about watching PIN 3 of the PA3004 protect IC.

Disconnecting AWM-124's pin 4 connection is NOT the SAME as pulling Q1.

1 to 2 seconds delay with a NEW CAP??
Going back to my third post of this thread, which states:

"Since Q2 on the protection board seems to be a common-failure item (according to other posts), I went ahead and replaced it with a Digikey 2N4401 transistor from some stock I had in the shop. It cross-referenced to an NTE123AP - same as the original 2SC1438. Still getting the cycling protection relay (with Q1 still removed) - same as before. Starting to wonder if the IC is bad....."

Caps have all been replaced per another previous post. The countdown delay for the relay does change with capacitance. It's normally around 2 seconds and roughly doubled when I added in another cap in parallel.

I'm at the point, now, where I'm looking for confirmation of operation of the protection relay with wires 4,5,6,7 & 8 disconnected from the protection board. My assumption is that, given voltages to the board are all correct and stable on pins 1,2,3,9 & 10, the relay should pull in and stay in after the initial delay. If not, like I'm experiencing, that means there are still issues on the board - and in my case two separate boards both tried with the same result.
 
Check FU6, or test short it or just replace it for now.

If it is old age failing, fu5 could carry the 13v dc load alone or smooth over the intermittent, showing up ONLY at the AC 20v output of the power supply.
Per a previous post, I already replaced FU6, but I'll try temporarily shorting it to see if I get any different readings. However, all my voltage readings at the board have always looked good, with exception of some ripple in the 65v supply, which appears to probably be normal, since I measured that same ripple on either side of the supply. Caps have been replaced for both the +65v and the -65v supplies.
 
PA3004 is a failure prone device, based on a lot of threads with this issue.
You have to verify if it is the PA3004 or an actual fault that is causing it to to drive the relay driver bjt.
Tests to be preformed
Do you have DC offset at a power amp channel?
Do you have the over current trigger activated, you can remove the bjt that drives this summing node at pin 4?
Grounding pin 4 will determine if there is a problem with PA3004
Does the relay operate correctly with the drive bjt operating properly?
Do you have a clean supply at pin 1, ~13VDC
Do you have -7.6VDC at pin 6?
Pin 7 is the ac presence detector, it should have a low voltage AC from the transformer secondary winding.

Good Luck
Rick
 
PA3004 is a failure prone device, based on a lot of threads with this issue.
You have to verify if it is the PA3004 or an actual fault that is causing it to to drive the relay driver bjt.
Tests to be preformed
Do you have DC offset at a power amp channel?
Do you have the over current trigger activated, you can remove the bjt that drives this summing node at pin 4?
Grounding pin 4 will determine if there is a problem with PA3004
Does the relay operate correctly with the drive bjt operating properly?
Do you have a clean supply at pin 1, ~13VDC
Do you have -7.6VDC at pin 6?
Pin 7 is the ac presence detector, it should have a low voltage AC from the transformer secondary winding.

Good Luck
Rick
Hi, Rick. Thanks for your reply. I will need to verify these things when I get back to the shop but, according to previous testing:
Regarding your question about DC offset - I went through the amplifier set-up procedure, according to the service manual, and was able to set offset and idle current correctly. I do have the wire from pin 4 of the protection board disconnected, which should eliminate any offset issues that might be happening.
Grounding pin 4 of the PA3004 does not stop the relay cycling.
Grounding pin 4 of the protection board does stop the relay cycling.
The relay cycles whether or not I have pin 4 of the protection board connected to the amps. Note: there have been a few times when the relay has engaged normally (usually first thing in the morning) and I have been able to connect all wires to the protection board and run audio through the receiver for maybe an hour or two before the relay starts to cycle again. At that point, even if I disconnect the wires from pins 4,5,6,7 & 8 of the protection board, the relay continues to cycle.
I do have clean 13.6vdc to pin 1 and clean -7.53vdc to pin 6 of the PA3004. I have 0.626vac at pin 7 of the PA3004 IC. Below are all my latest voltage measurements:

Q1
E 13.3vdc
B 13.3vdc
C 0v

Q2
E 0v
B 0 (relay off); 0.7vdc (relay on)
C 67vdc (relay off); 0v (relay on)

Protection Board
1 19.8vac
2 -53.06vdc
3 0v
4 disconnected
5 disconnected
6 disconnected
7 disconnected
8 disconnected
9 13.56vdc
10 67.3vdc

PA3004 IC
1 13.6vdc
2 N/A
3 0v (relay off); 0.7vdc (relay on)
4 -0.014vdc
5 0v
6 -7.53vdc
7 0.626vac
8 1.5vdc ~ 5.5vdc
 
Grounding pin 4 of the protection board does stop the relay cycling.
It keeps the relay off as it should, since it turns Q1 on to drive the summing node.
pin 3 should not be cycling.
PA3004 is faulty, get a spare, put in a SIP IC socket so it easy to change out if fails again.
 
It keeps the relay off as it should, since it turns Q1 on to drive the summing node.
pin 3 should not be cycling.
PA3004 is faulty, get a spare, put in a SIP IC socket so it easy to change out if fails again.
I already have a spare PA3004 on order. Hoping to receive it later this week. I'm hoping you're right about the faulty IC - it'll make my life easier if I can replace it and have my relay cycling problem go away!
 
What is the dc voltage at the anode of D1 on the Protection board? Is it clean DC looking at it with the scope?
I have -13.28vdc at the anode of D1 on the protection board. O-scope shows me a nice, flat line @ 5v/division.
 
A note on the PA3004 I ordered from Ebay: Only 1 seller was listed as being within the US (California) so, although it wasn't the cheapest, I went with them since the delivery date range was decent and I thought I would get it sooner since it was already in the US. I noticed my payment went to a company in Hong Kong. Then a shipping notification showed a label had been created in California, but the USPS was waiting for acceptance of the item. That was five days ago, and things haven't changed since then. My assumption is that the part is in China (same as all the other PA3004's available), but a shipping label was prepared by a partner company in the US, creating the impression that the part is in the states. Although I can't prove anything, this looks like what's going on, so just an FYI to others who might be purchasing something like this from Ebay.

Since I have two boards with the same suspected problem, I ordered another PA3004 from another company in China. Guess we'll see which one gets here first. If it turns out the IC isn't the issue, I'm okay with having a couple spares - these things probably won't be available forever.
 
I know they are expensive, too bad, Pioneers failure imo was to get into custom ics, I wish they just kept with the original discrete design that they used for years or used a standard ic mfg, even a later SX-D7000 uses a discrete protection ckt, go figure.
something to make/design one day is a small pcb that will replace it.
here's hoping the new parts work out for you.
 
I know they are expensive, too bad, Pioneers failure imo was to get into custom ics, I wish they just kept with the original discrete design that they used for years or used a standard ic mfg, even a later SX-D7000 uses a discrete protection ckt, go figure.
something to make/design one day is a small pcb that will replace it.
here's hoping the new parts work out for you.
Really, they weren't too bad. Most can be had for under $20, including shipping. I just have to wait for the slow boat from China. Either way this works out, I'm learning something.

It would be nice to have a write-up on the procedure for checking protection board issues. Basically, check for proper, stable voltages (and ground) to the PA3004. Leave the preamp/power amp out/in jumpers disconnected. Disconnect speakers. Then it's down to pin 4 of the board and pin 4 of the IC. Not sure if the wire to pin 4 of the board should be disconnected or not (my guess is disconnect it). If the relay operates normally at this point, there's a problem with one or both of the amp boards. Continuing on, ground pin 4 of the protection board, then pin 4 of the IC - the results of the relay action during the grounding of these two pins should narrow down the problem to either the IC or the protection board.

Does that sound sort of correct?
 
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Really, they weren't too bad. Most can be had for under $20, including shipping. I just have to wait for the slow boat from China. Either way this works our, I'm learning something.

It would be nice to have a write-up on the procedure for checking protection board issues. Basically, check for proper, stable voltages (and ground) to the PA3004. Leave the preamp/power amp out/in jumpers disconnected. Disconnect speakers. Then it's down to pin 4 of the board and pin 4 of the IC. Not sure if the wire to pin 4 of the board should be disconnected or not (my guess is disconnect it). If the relay operates normally at this point, there's a problem with one or both of the amp boards. Continuing on, ground pin 4 of the protection board, then pin 4 of the IC - the results of the relay action during the grounding of these two pins should narrow down the problem to either the IC or the protection board.

Does that sound sort of correct?

Yes, I believe so. Grounding Protection Board pin 4 should cause the relay to turn off, as this is the overload fault input. Grounding the PA3004 pin 4 should not affect the relay UNLESS there is an overload or dc offset fault signal coming in causing the relay to be off. If so then the relay should pull in, as grounding PA3004 pin 4 swamps the incoming 'fault' indication.

It appears we have exhausted the tests and have nothing left to look at until one of your new PA3004s arrive. The real conundrum for me is that the second board behaves the same as the original. Perhaps that is why it was for sale:(:dunno:.

The least expensive (individually) I have found is to buy 10 PA3004s at one time, with free shipping, for $110. On our favorite auction site of course. Every other listing I have found is slightly to greatly more expensive.

I am hoping to acquire a protection board and set up a test bed to determine directly the limits and operational parameters of the PA3004. :idea:
 
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Yes, I believe so. Grounding Protection Board pin 4 should cause the relay to turn off, as this is the overload fault input. Grounding the PA3004 pin 4 should not affect the relay UNLESS there is an overload or dc offset fault signal coming in causing the relay to be off. If so the the relay should pull in, as grounding PA3004 pin 4 swamps the incoming 'fault' indication.

It appears we have exhausted the tests and have nothing left to look at until one of your new PA3004s arrive. The real conundrum for me is that the second board behaves the same as the original. Perhaps that is why it was for sale:(:dunno:.

The least expensive (individually) I have found is to buy 10 PA3004s at one time, with free shipping, for $110. On our favorite auction site of course. Every other listing I have found is slightly to greatly more expensive.

I am hoping to acquire a protection board and set up a test bed to determine directly the limits and operational parameters of the PA3004. :idea:
I'm going on the assumption the spare protection board I purchased has a faulty PA3004, as well. I'd like to connect and test that other board the same way I tested my original and get both boards so they can be connected up and function normally.

As I'm sure others have done, I've spent a fair amount of time scouring the internet for a schematic or data sheet of the PA3004, but have come up empty-handed. It would be nice to have a full understanding of the inner workings of it and, as Rick mentioned in an earlier post, have the ability to build a circuit that behaves the same using individual components for, if nothing else, a more-robust alternative to the PA3004.

While I wait for the replacement IC's, I biding my time upgrading the dial and indicator lamps to LEDs. I've also been doing some "body work" on the cover to hide some of the nicks and spots on the rear corners that are missing the veneer. My collection of wood putty, oils and furniture markers grows steadily as I work my way through figuring out the best way to patch up the missing veneer. I've got a Realistic STA-2080 that I'm itching to get into, although it will only entail an LED upgrade, cleaning and a little veneer work up front.
 
Yes, that seems elusive. The block diagram seems to be the only readily available info:

PA3004Pinout.jpg
 
Yes, that seems elusive. The block diagram seems to be the only readily available info:

PA3004Pinout.jpg
I had a look at the protection circuit for an SX-950 this morning, thinking it might be similar-enough to adapt to an SX-980. Not so much - not without a lot of adaptation, anyway. I finally received a shipping confirmation for my first PA3004 - I should be able to install it by the end of the week. Hoping that closes this chapter of issues.
 
Yes, I believe so. Grounding Protection Board pin 4 should cause the relay to turn off, as this is the overload fault input. Grounding the PA3004 pin 4 should not affect the relay UNLESS there is an overload or dc offset fault signal coming in causing the relay to be off. If so then the relay should pull in, as grounding PA3004 pin 4 swamps the incoming 'fault' indication.

It appears we have exhausted the tests and have nothing left to look at until one of your new PA3004s arrive. The real conundrum for me is that the second board behaves the same as the original. Perhaps that is why it was for sale:(:dunno:.

The least expensive (individually) I have found is to buy 10 PA3004s at one time, with free shipping, for $110. On our favorite auction site of course. Every other listing I have found is slightly to greatly more expensive.

I am hoping to acquire a protection board and set up a test bed to determine directly the limits and operational parameters of the PA3004. :idea:
The slow boat from China must have had a tail wind - my new PA3004 arrived yesterday. I installed it first thing this this morning, double-checked my solder connections and my jumper wires to the protection board, turned on the power and.......the relay continues to cycle! OMG. I disconnected wires from pins 4,5,6,7 & 8 of the protection board. I rechecked voltages on the PA3004 - all the same as my last check - everything checks normal. Grounding pin 4 of the protection board prevents the relay from engaging. Grounding pin 4 of the PA3004 does nothing - relay still cycles. Everything tests and behaves exactly the same as before. It appears it's time to go back to square 1 and start over. I'll read over some of the old posts and start there. I might pull Q1 as Mark advised and see what result I get.
 
Hmmm, that stinks, but it points back to power supply, as nothing else is connected. Do you still have that noise on the peaks of the +65v ripple? When you pull Q1, pull Q2 as well, then check PA3004 pin 3 to see if it is still cycling.
 
Grounding pin 4 of the protection board prevents the relay from engaging. Grounding pin 4 of the PA3004 does nothing - relay still cycles.
That is interesting. Look at the ground potential difference between the ACTUAL metal of the PA3004's pin 5 and the actual metal of the chassis. Watch it through a couple of "cycles" first.

Quite frankly, grounding the AWM-124 protection board's pin 4 is just signalling a protect condition, as pulling it LOW is the function of both AWH-073 power amp channel's Q8s.


Hmmm, that stinks, but it points back to power supply, as nothing else is connected. Do you still have that noise on the peaks of the +65v ripple? When you pull Q1, pull Q2 as well, then check PA3004 pin 3 to see if it is still cycling.
I know there is a hankering to rush and "git er dunn", but PLEASE do this in a methodical order, you would be setting up a double double blind,
so please do q1 first, then see if pin 3 and q2 are behaving.
 
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That is interesting. Look at the ground potential difference between the ACTUAL metal of the PA3004's pin 5 and the actual metal of the chassis. Watch it through a couple of "cycles" first.

Quite frankly, grounding the AWM-124 protection board's pin 4 is just signalling a protect condition, as pulling it LOW is the function of both AWH-073 power amp channel's Q8s.

I know there is a hankering to rush and "git er dunn", but PLEASE do this in a methodical order, you would be setting up a double double blind,
so please do q1 first, then see if pin 3 and q2 are behaving.

Mark, I agree things need to be done methodically. Please take the lead, if you wish, and I will learn from your procedures.
 
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