Pioneer SX-980 Protection Relay Kicking Out

[Brivan]

That was my assumption - by leaving the jumpers out, I was eliminating everything before the amplifier boards. And those were the only things I physically moved before the problem started. This morning, I moved wires, pressed on boards, etc - all while the relay was cycling, but I could never physically move anything that would definitely affect the relay cycle. One thing to note - the longer I leave the receiver on with the relay cycling, the more sporadic the cycling becomes - it might run for several minutes or only a fraction of a second. Since it's staying engaged for longer periods of time, I'll try to get some voltage readings and will post them. BTW I do have another "good" protection board coming from Ebay. I took voltage readings at the speaker terminals while the relay was engaged - both sides are at .1 - .2 mV.

 

[merlynski]

That was my assumption - by leaving the jumpers out, I was eliminating everything before the amplifier boards. And those were the only things I physically moved before the problem started. This morning, I moved wires, pressed on boards, etc - all while the relay was cycling, but I could never physically move anything that would definitely affect the relay cycle. One thing to note - the longer I leave the receiver on with the relay cycling, the more sporadic the cycling becomes - it might run for several minutes or only a fraction of a second. Since it's staying engaged for longer periods of time, I'll try to get some voltage readings and will post them. BTW I do have another "good" protection board coming from Ebay. I took voltage readings at the speaker terminals while the relay was engaged - both sides are at .1 - .2 mV.

Since this occurred after you did a recap/refurb (if I recall correctly) carefully recheck that any transistors replaced are properly oriented (ECB, EBC, etc.) by looking at the datasheet and the PCB connections (not just the labeling, sometimes printing is wrong on the board) and ecaps are not backwards (again don't blindly trust labels). Note that Pioneer shows boards from the foil side, this has fooled many of us in the past, because part orientation is flipped over in the picture.

 

[merlynski]

For what it's worth, most of the experienced techs here are not in favor of replacing whole boards unless it is physically damaged (burnt or broken beyond repair) because it will have the same "old" parts as the original, and disturbing the wire wrap creates more problems than it may solve. YMMV The only part you cannot replace with modern parts, as far as I know, is the PA3004. The resistors, caps, transistors and relay subs are available.

 

[Brivan]

I basically bought the protection board for the IC. I agree - it's far easier to replace components than to deal with the wire wrapping of a replacement board. I did pay attention to the orientation of the Q1 and Q2 transistors when I replaced them - thanks to another Audiokarma post. I grounded the collector of Q2, causing the relay to close, for the readings below. Voltages that changed when the collector of Q2 was ungrounded and relay was allowed to cycle off are noted.

Protection Board Pins:
1 19.72vac
2 -53.3vdc
3 0v
4 13.4vdc
5 -0.022vdc
6 -0.017vdc -0.092vdc (relay off)
7 -0.001vdc -0.112vdc (relay off)
8 -0.024vdc
9 13.73vdc
10 66.8vdc

Q1
E 13.73vdc
B 13.73vdc
C -0.017vdc

Q2
E 0v
B 0.002vdc 0.702vdc (relay off)
C 67.3vdc 0.059vdc (relay off)

IC
1 13.49vdc
2 N/C
3 0.35vdc 0.002vdc (relay off)
4 -0.014vdc
5 0v
6 -7.58vdc -7.51vdc (relay off)
7 -0.021vdc -0.03vdc (relay off)
8 1.5vdc ~ 5.5vdc (depending on capacitor charge state)

 

[merlynski]

Protection Board Pins:
1 19.72vac
2 -53.3vdc
3 0v
4 13.4vdc
5 -0.022vdc
6 -0.017vdc -0.092vdc (relay off)
7 -0.001vdc -0.112vdc (relay off)
8 -0.024vdc
9 13.73vdc
10 66.8vdc

Q1
E 13.73vdc
B 13.73vdc
C -0.017vdc

Q2
E 0v
B 0.002vdc 0.702vdc (relay off)
C 67.3vdc 0.059vdc (relay off)

IC
1 13.49vdc
2 N/C
3 0.35vdc 0.002vdc (relay off)
4 -0.014vdc
5 0v
6 -7.58vdc -7.51vdc (relay off)
7 -0.021vdc -0.03vdc (relay off)
8 1.5vdc ~ 5.5vdc (depending on capacitor charge state)

PCB pins all look OK to me.

Q1 normal readings for non-overload conditions.

I was unclear about Q2, what I expect to see:
Q2
E 0v
B 0.002vdc(relay off) 0.702vdc (relay on)
C 67.3vdc(relay off) 0.059vdc (relay on)
if so Q2 appears OK, and relay itself functioning normal.

IC
1 => 6 look OK
7 should be constant ~ 0.75vac, this is the immediate AC detect pin to mute the output quickly at power off.
8 1.5vdc ~ 5.5vdc (depending on capacitor charge state) This one concerns me. It controls the relay ON delay time and should charge up to ~+7.2vdc and stay unless an input causes it to drop. When you shorted the Collector of Q2 to ground how did pin 8 act? Make sure C4 and/or C5 are not reversed or leaking, either might cause the relay to cycle without affecting the other inputs. If the caps are good and not reversed I suspect the IC, as you were leaning toward.
If you don't mind my asking what was paid for the whole prot board?

 

[Brivan]

PCB pins all look OK to me.

Q1 normal readings for non-overload conditions.

I was unclear about Q2, what I expect to see:
Q2
E 0v
B 0.002vdc(relay off) 0.702vdc (relay on)
C 67.3vdc(relay off) 0.059vdc (relay on)
if so Q2 appears OK, and relay itself functioning normal.

IC
1 => 6 look OK
7 should be constant ~ 0.75vac, this is the immediate AC detect pin to mute the output quickly at power off.
8 1.5vdc ~ 5.5vdc (depending on capacitor charge state) This one concerns me. It controls the relay ON delay time and should charge up to ~+7.2vdc and stay unless an input causes it to drop. When you shorted the Collector of Q2 to ground how did pin 8 act? Make sure C4 and/or C5 are not reversed or leaking, either might cause the relay to cycle without affecting the other inputs. If the caps are good and not reversed I suspect the IC, as you were leaning toward.
If you don't mind my asking what was paid for the whole prot board?

A couple pics of the protection board. All caps on the board have been replaced (except the cap across pins 2 and 3), and they appear to be in correct orientation. With Q2's collector shorted to ground, the relay holds closed, but I'm still seeing a charge/discharge cycle on pin 8. In fact, any voltages measured on Q2 and the IC continue to vary in the same pattern as if the relay was cycling. Only pins 6 & 7 on the protection board are now holding steady. I paid $31, including shipping, for the board. I didn't think that was too bad, considering the value/rarity of these receivers continues to climb. Sorry for the mix-up - I appeared to have the Q2 measurements turned around between the off- and on-state measurements.

 

[merlynski]

View attachment 1268525 View attachment 1268527
A couple pics of the protection board. All caps on the board have been replaced (except the cap across pins 2 and 3), and they appear to be in correct orientation. With Q2's collector shorted to ground, the relay holds closed, but I'm still seeing a charge/discharge cycle on pin 8. In fact, any voltages measured on Q2 and the IC continue to vary in the same pattern as if the relay was cycling. Only pins 6 & 7 on the protection board are now holding steady.

OK, that is what I expected, but not what it should be doing. If you ground pin 4 does it stop cycling? Probably not since Q1 removed did not stop it . . Pin 8 grounded should stop it. I would not ground any other pins. Do you have an oscilloscope? There may be signals on the IC inputs that are too fast to see with a DMM. Look at each pin for unexpected transients, especially 1, 4, 6, 7, & 8.
Looking more like it is the IC: the internal constant current drive to charge caps on pin 8 flaking out.

EDIT: more text

 

[Brivan]

Grounding pin 4 does not stop the cycling, but grounding pin 8 does stop it. I have an o-scope, so I'll check the pins on the IC and can maybe post pics of anything unusual - if I can get the o-scope image to stabilize long enough to get a photo.

 

[Brivan]

OK, that is what I expected, but not what it should be doing. If you ground pin 4 does it stop cycling? Probably not since Q1 removed did not stop it . . Pin 8 grounded should stop it. I would not ground any other pins. Do you have an oscilloscope? There may be signals on the IC inputs that are too fast to see with a DMM. Look at each pin for unexpected transients, especially 1, 4, 6, 7, & 8.
Looking more like it is the IC: the internal constant current drive to charge caps on pin 8 flaking out.

EDIT: more text

Voltages on all IC pins noted above are stable, with exception of pin 7, which gives me a square-ish wave of about 1.5 volts with a cycle of about 15mS. Since this is fed from pin 1 of the protection board, which is 21vac, the waveform makes sense. I went through all the pins on the IC and made sure I had good contact with my probe, but nothing strange seen on the scope screen, other than the capacitor charge/discharge on pin 8.

 

[merlynski]

Voltages on all IC pins noted above are stable, with exception of pin 7, which gives me a square-ish wave of about 1.5 volts with a cycle of about 15mS. Since this is fed from pin 1 of the protection board, which is 21vac, the waveform makes sense. I went through all the pins on the IC and made sure I had good contact with my probe, but nothing strange seen on the scope screen, other than the capacitor charge/discharge on pin 8.
View attachment 1269000

Looks exactly like what I expected to see on pin 7, 16.6 ms (60Hz) rectifier-clipped wave. Looks like we have eliminated everything except the PA3004. Internal failure. I have seen it said here on the forum that the IC rarely fails, guess this is one of those times . When your good board arrives and you swap the IC we should know for sure. When do you expect it?

 

[Brivan]

According to Ebay, I should have it waiting for me in my mailbox today. I'll hopefully get it installed tomorrow. I'm on the fence as to replace just the IC or the whole board. The board wiring will be more involved, but unsoldering/resoldering an old IC might be hard on it, too.
Also, I read some older posts you provided links to. According to markthefixer, pin 3 of the IC should have 0.7vdc on it in order to activate Q2 (also shown in the service manual). When I took my original Q2 base reading, the relay was still holding in long-enough on it's own to get an accurate reading - hence the .702vdc I posted earlier. By the time I got to taking readings from the IC, the relay had started to cycle again and I got about 0.35vdc on pin 3 of the IC - less than what is needed to keep Q2 activated. Some of this can probably be attributed to the brief amount of time I have to take the reading (considering how quickly the relay jumps from off, to on, to back off again) but I'm hoping I'm we're on to something with a bad PA3004.

 

[merlynski]

According to Ebay, I should have it waiting for me in my mailbox today. I'll hopefully get it installed tomorrow. I'm on the fence as to replace just the IC or the whole board. The board wiring will be more involved, but unsoldering/resoldering an old IC might be hard on it, too.
Also, I read some older posts you provided links to. According to markthefixer, pin 3 of the IC should have 0.7vdc on it in order to activate Q2 (also shown in the service manual). When I took my original Q2 base reading, the relay was still holding in long-enough on it's own to get an accurate reading - hence the .702vdc I posted earlier. By the time I got to taking readings from the IC, the relay had started to cycle again and I got about 0.35vdc on pin 3 of the IC - less than what is needed to keep Q2 activated. Some of this can probably be attributed to the brief amount of time I have to take the reading (considering how quickly the relay jumps from off, to on, to back off again) but I'm hoping I'm we're on to something with a bad PA3004.

I did see what you are referring to. My thinking was that if the relay was pulling in, even intermittently, then the voltage on pin 3 was sufficient to turn on Q2 (when it was on) and the cycling was causing the DMM to "average" the voltage, so it appeared lower. When grounding the collector of Q2 held the relay in it told me that the relay was not part of a feedback loop causing the cycling, plus you had replaced Q2 already . . . The last SX-780 I worked on had 'Q2' failed and pin 3 was at ~+13vdc (open BE junction). The constant current source into the B of Q2 had plenty of drive, and the (my) PA3004 was working correctly. Did you check pin 3 when Q2 was removed? That was where I was going when we started this and I erroneously said Q1 instead of Q2. My fault .

 

[Brivan]

I did see what you are referring to. My thinking was that if the relay was pulling in, even intermittently, then the voltage on pin 3 was sufficient to turn on Q2 (when it was on) and the cycling was causing the DMM to "average" the voltage, so it appeared lower. When grounding the collector of Q2 held the relay in it told me that the relay was not part of a feedback loop causing the cycling, plus you had replaced Q2 already . . . The last SX-780 I worked on had 'Q2' failed and pin 3 was at ~+13vdc (open BE junction). The constant current source into the B of Q2 had plenty of drive, and the (my) PA3004 was working correctly. Did you check pin 3 when Q2 was removed? That was where I was going when we started this and I erroneously said Q1 instead of Q2. My fault .

Not a big deal. I think I may have already replaced both Q1 and Q2 at that point, making no difference in the relay cycling problem. I just continuity-tested the original Q1 and Q2 transistors and they checked fine - which I know doesn't guarantee anything, but since nothing changed after replacing them, I'm fairly confident the replacement transistors are good. I now have the protection board removed, with plenty of photos and notes telling me where the wires go on the replacement board that I'll hopefully get installed tomorrow. I thought it was best to restart with a replacement board, so I can eliminate all the changes I've made to the original (caps and transistors replaced, IC and some resistors resoldered). The wires to the board are all a relatively small gauge, so I'm hoping it won't take much heat to get them attached to the outer ends of the pins, avoiding accidental desoldering of the pins where they attach to the board.

 

[merlynski]

I look forward to seeing the results of the board swap .

 

[Brivan]

I look forward to seeing the results of the board swap .

I think I'll try to temporarily connect the new board using jumpers - unless it gets too messy and the chances of things coming into contact with other things is too great. Then , if (please lord I hope not) the problem continues, I can go back to my original board for further testing.

 

[merlynski]

I think I'll try to temporarily connect the new board using jumpers - unless it gets too messy and the chances of things coming into contact with other things is too great. Then , if (please lord I hope not) the problem continues, I can go back to my original board for further testing.

Be careful, the outputs from your power amps go through that board. One slip could fry both of the power amps, the output transistors and the power supply. .

 

[Brivan]

Be careful, the outputs from your power amps go through that board. One slip could fry both of the power amps, the output transistors and the power supply. .

Well, I know what the problem isn't - the replacement protection board does the same thing - relay cycling. Heavy sigh. Oh, well - now I know what I don't have to work on! Connecting the jumpers wasn't all that bad - I just went through twice and verified my connections.

 

[Brivan]

I've now removed jumpers from pins 4, 5, 6, 7 and 8 of the protection board (all at the same time), so all I'm providing are the necessary voltages for the board to operate. Amazingly, the relay continues to cycle. I rechecked voltages going to the protection board - all look good and are the same as what I posted earlier when I measured them going to my old protection board. So, do I have another bad board? This is getting pretty insane.

 

[Brivan]

I rechecked voltages to the protection board using my o-scope so I could look for funny waveforms. Everything looks good, except for the 66v on pin 10. I've got almost a 5-volt ripple there. Do you think that would make my protection board crabby?

 

[merlynski]

That is wicked looking ripple for a power supply rail . Is it the same on pin 19 of the power supply board? Check PS FU3 and FU4, rectifiers D1-4 and C11 (reversed?).
Scope all the other outputs of the PS also, as well as DC voltages.