Brivan
Well-Known Member
AC voltage to pin 7 of the PA3004 is 34mV. DC voltage to that same pin is 0v.
Pioneer SX-980 Protection Relay Kicking Out
- Thread starter Brivan
- Start date
Brivan
Well-Known Member
Gotcha. I've seen that posted before - I apparently was having a brain fart. No, no DBT connected. No speakers connected, no pre-out/in jumpers installed, wires to pins 4,5,6,7 & 8 of the protection board disconnected, no speakers selected, volume at 0.
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petehall347
the brandy coffee man
am wondering how much AC is on the other pins ? with AC supply disconnected from the board
Brivan
Well-Known Member
Interesting you're asking about that. I was just taking those measurements when I saw your question. With the AC connected, I get an expected AC signal on pin 7 of the PA3004, but I also get this waveform on pin 6 of the PA3004:
With the AC disconnected from the board, none of the pins on the PA3004 show any AC waveforms.
Edit: I installed my original PA3004 in the socket to see if it made any difference. With 21vac connected to pin 1 of the protection board, I no longer see any AC on any pins of the PA3004, except for pin 7.
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Brivan
Well-Known Member
Yeah, that was kind of a surprise for me, too. My normal voltage reading with a PA3004 installed is -7.53vdc at pin 6. I'd love to have a complete schematic of the inner-workings of the PA3004. Right now, that's where my journey has ended. There is just nothing else I can find wrong. I have one more new PA3004 that will be delivered tomorrow. It's an extreme longshot, but maybe the noisy ground I had compromised the other PA3004s I had installed. Waaaay doubtful, but it's all I've got to go on, right now. Since I have a handy-dandy SIP socket installed, putting in a new one will take a few seconds.
petehall347
the brandy coffee man
all i wondered is with it still cycling with AC disconnected it may have been getting the AC from elsewhere . it shouldn't be turning on the relay driver without it .
I looked at post #115, the block diagram, Ct (pin 8) should be charging up to some dc voltage?, I do not think it should be zero V as in your case, there is a CC gen used to charge the ecap so it must be toast or the ecap is shorted or a really low C to cause it to cycle.
Brivan
Well-Known Member
That's a good point I hadn't really thought about. I assumed the PA3004 was causing a relay cycle based on the fact that I was still seeing the timing capacitor charge/discharge at pin 8 of the PA3004. I just disconnected the AC input from pin 1 of the protection board, then probed pin 3 of the PA3004 with my o-scope, and it's definitely showing a brief 12vdc output. So, the PA3004 isn't behaving correctly to a removed AC source.
Brivan
Well-Known Member
The timing capacitor does charge up, then it rapidly discharges at the same time pin 3 of the PA3004 gives a quick 12vdc pulse (the voltage is high, but I have Q2 removed. When Q2 is back in place the pulsed voltage is only 0.7vdc). The timing capacitor drops to about 1vdc, then rapidly discharges once it hits about 6vdc. I always have that timing capacitor cycle as long as the correct input voltages are provided to protection board pins 2, 9 & 10. And ground to pin 3. My apologies if I noted 0v at pin 8 of the PA3004 when I shouldn't have.
merlynski
Curmudgeon Electronicist
It appears that the PB is working correctly (except removing AC). Pin 3 goes to the + rail (~+12vdc) because Q2 is removed, so there is no current sink. If you put Q2 back in pin 3 will only increase to one forward biased base junction voltage (~+0.7vdc). But according the posts Q2 in or out makes no difference to whether the circuit cycles or not. Does anybody see a different effect?
Brivan, can you connect your spare Prot Board to power supplies, etc to simulate the SX-980 without actually connecting it to a Receiver? i.e. ground, +65vdc, +13vdc and -50vdc and see if it still cycles?
Brivan, can you connect your spare Prot Board to power supplies, etc to simulate the SX-980 without actually connecting it to a Receiver? i.e. ground, +65vdc, +13vdc and -50vdc and see if it still cycles?
Brivan
Well-Known Member
I had thought about that. The +65vdc and -50vdc power supplies might be a little tough to find - I don't think I have any that go that high, but I'll look. Maybe someone here can recommend a reasonably-priced one that would give me the ability to provide both voltages. I was also wondering if I could substitute in a protection board supply voltage from an external source without damaging the receiver.
Brivan
Well-Known Member
Recapping the power supply this morning (for the caps that haven't already been replaced). The 2200uf cap has a third leg (like me - chuckle, chuckle) that appears to just there for stability - the trace on the board is just a round spot that doesn't connect to anything, so I assume that's electrically unimportant.
Brivan
Well-Known Member
Okay, thanks. Caps have all been replaced, resoldered leads to all of the resistors 1 watt and above, resoldered leads to the four, large diodes. Powered on and still have charge/discharge of the timing cap and the brief 12vdc transition on pin 3 of the PA3004. Checked voltages to the protection board and the PA3004 - all basically the same as before.
Brivan
Well-Known Member
Thanks for the schematic! I checked my variac and it doesn't appear to have isolation between input and output. My newly-purchased SX-980 will arrive tomorrow, so I might wait to see if I can do some comparisons between it and my problem child. I thought I would have another PA3004 by now, but it's taking longer than expected.View attachment 1285537 You have a variac, you can whip together a low current supply with that and a few components. Be careful though, if your variac is not isolated from hot/neutral you may be at risk of electrical shock from this circuit.
Brivan
Well-Known Member
Well, we've had some results here, this morning. I've always noticed how clipped that 21vac looked on pin 1 of the protection board, as well as the .75vac on pin 7 of the PA3004. I checked the other AC lines coming from the transformer, and they're also less than perfect. Most show irregular peaks - not quite clipped, but not smooth, either. The clipping is most obvious on pins 12, 13 & 14 of the power supply board.
I grabbed a 20vac old school wall wart, made sure it was isolated (it was), removed the 21vac supply from pin 1 of the protection board and subbed in a lead from the 20vac wall wart. Powered everything up and, miraculously, I saw my timing capacitor stabilize at about 6.5vdc. 12vdc coming from pin 3 of the PA3004. Glory, hallelujah! I promptly powered everything off, then soldered Q1 and Q2 back in the protection board. Powered it all up and the relay engages and stays that way - like it's supposed to!
So, I did some waveform checks with the o-scope. This is the 20vac from my wall wart while connected to the receiver - nice-looking AC:
This is the 21vac supplied by the receiver while disconnected from the protection board. It's clipped - especially on the positive swing:
This is incoming power from my power strip. Again, nice-looking AC:
I checked D6 & D7 on the power supply board - they tested fine. I also measured the voltage at the junction of D6 & D7 and got about 25.7vdc - just a tad high, but all my other AC voltages are a tad high, generally. So, what am I looking at here? A transformer with a crappy winding or two? I don't see where anything else can make a difference in the waveforms coming from the transformer.
