Pioneer SX-750 Protection Relay not Clicking

[vega2k]

I have read through the various older threads that are related to my issue, but I am not getting to a solution. I proactively recapped the Power Supply & Protection Assembly (AWR-099) on my previously working SX-750, with much regret because when I was done, there were sparks!... I found a trace bridge. After I repaired bridge, replaced R25, which looked burnt and then checked just about everything else, I tried turning it on again with a DBT, but protection relay does not click. From other thread recommendations, when I remove Q6, the relay DOES click normally. Since relay clicks normally without Q6, does that automatically mean Q6 is bad? I assume not, because, I have tested this transistor and I cannot detect anything wrong with it. When I measure Q6 voltage drop from BE, l get 0.684v, BC drop is 0.678v. When I reverse leads, I get OL, so looks normal. Here's what may be a stupid question, What should I be measuring when I measure EC (emitter-collector) on Q6??? Should it read OL or a value? With the Q6 transistor In circuit but unit turned off, on EC I am getting a reading of 1.9v and a different value when I reverse leads. Am I incorrect in assuming transistor is working ok based on measurements? Can anyone offer direction to where I can go next? I would really appreciate any help. I feel like a moron for messing-up a beautiful working unit!

 

[markthefixer]

where was the trace bridge? gotta look at both sets of circuits affected.
R25 is a 68k ohm resistor - that's pretty hard to hurt. too much resistance to push enough current through for destructive heating.
I don't see many possibilities for mistaken identification with that part, located like that in the corner of the board...

Q6 is not necessarily automatically bad, and in fact there is a LOT of things going on with it.

Did you use any ksa733 (q5) or ksc945(q6) transistors? I have not found a SX-750 transistor list.
If you did, they have an EBC pinout EXCEPT if they are the "C" variant (ksa733C, ksc945C) which then makes their pinout ECB.
The C variant transistors do NOT have any external markings to indicate their special status - you need to use an ohmmeter to "find" the base lead.
https://www.audiokarma.org/forums/i...lar-junction-transistor-testing-basics.43186/

so

remove q5 and reinstall q6. that's the continuing test,
without q5, there is no DC or overcurrent protect, yet the other on / off and timing functions should work.
q5 tells q6 to discharge c8.

 

[merlynski]

 

[vega2k]

Hey there mikethefixer. Thank you for the reply.

The solder/trace bridge occurred at the PS & Protect Assembly board corner by C7 and C8. After reading your response, I did notice C8 appeared to have some residue underneath, which was not there when I recapped. Perhaps it overheated? leaked? was fried?.... So I did change it out for a new one, but that did not fix the problem.

I then removed Q5 and as you said, the protection relay DID click. These are my measurements of Q5 (out of circuit FYI - I determined it is a PNP transistor because voltage drops occur when I connect the negative probe to the Base (B) and the positive probe to the Emitter (E) and to the Collector (C) pins.
- BE: 0.645v
- BC: 0.632v
- EC: LO
To me, this seems to indicate that Q5 is fine.... Am I wrong?

I have not changed out any of the transistors yet. They are all original. Based on research in AK threads, I did proactively place a Digikey order yesterday as follows:
Q5 - KSA992FBU
Q6 - ordered two options: KSC1845FTA and/or KSC2383YTA
I also ordered transistors for Q1 to Q4 and Q9 and Q11, mainly to optimize shipping cost.

So, so far:
- when I remove Q6 (with everything else in place), relay clicks.
- when I remove Q5 (with everything else in place), relay clicks.
- I replaced C8 (looked damaged)
- I replaced R25 (just in case)
- I replaced R33 (looked burned after trace bridge)

I assume my next steps will be:
- Just in case, replace Q5 and Q6...

What else can I try? Please "fix" me!!!

 

[merlynski]

Here is what I would use for the protection circuit transistors:
Q1, Q2, Q3, Q4: 512-KSC1845FTA
Q5: 512-KSA992FTA
Q6: 512-KSC2383YTA
Q7: 512-KSC2690AYSTU
D5, D6, D7: 1N4148,
Diodes probably do not need replaced unless they have failed.

These are the inputs to the protection circuit . . .
Measure dcv on AWR-099 pins:
Pin 8:
Pin 10:
Pin 9:
Pin 11:
Pin 1:
Pin 4:
Pin 17:
Measure acv on AWR-099 pins:
Pin 6:
Pin 7:

Power Supply Voltages
Also measure dcv on AWR-099 pins:
Pin 24:
Pin 23:
Pin 22:


EDIT: more

 

[vega2k]

Here are the measurements I took. These measurements are with the relay clicked (Q5 transistor removed from the PS&Protect board):
">" denotes those pins you listed:
>1 30mv
2 30mv
3 26mv
>4 26mv
5 6.3vac
>6 6.3vac
>7 6.3vac
>8 35mv
>9 21mv
>10 24mv
>11 31mv
12 0.9mv
13 -0.1mv
14 -0.1mv
15 -0.1mv
16 -34v
>17 -33v
18 33v
19 1.1mv
20 1.1mv
21 1.1mv
>22 12.3v
>23 30v
>24 30v

In addition, just in case, amp board measurements:
22 ~26mv fluctuating
36 ~30mv fluctuating


Thank you all again for the help!

 

[merlynski]

You are welcome!
I reorganized them back to the way they were so I could read them easily. It is easier (for me anyway) if you just copy and paste the list as it is, then enter the measurements. The extra info and reordering make it harder to understand.

Measure dcv on AWR-099 pins:
Pin 8: 35mv
Pin 10: 24mv
Pin 9: 21mv
Pin 11: 31mv
Pin 1: 30mv
Pin 4: 26mv
Pin 17: -33v

Measure acv on AWR-099 pins:
Pin 6: 6.3vac
Pin 7: 6.3vac

Power Supply Voltages
Also measure dcv on AWR-099 pins:
Pin 22: 12.3v
Pin 23: 30v
Pin 24: 30v

Those first ones look just fine, they are the inputs to the protection circuit, the last three are a little low, but still within 10% of nominal.
Put Q6 (a new one if you have it) back in.
Measure dc volts on the cathode of:
D5:
D6:
D7:
please.

 

[vega2k]

Pin order matters, got it and it makes sense. Here's the measurements I took of D5. D6, D7(cathode side). I do not have the transistor replacements yet, so I am using the originals.

Measurements with Q5 transistor NOT INSTALLED on board (Relay clicked):
D5 ~5v fluctuating
D6 ~26v fluctuating
D7 ~8v to 10v fluctuating

Measurements with Q5 transistor INSTALLED on board (No Relay click):
D5 ~7 to 9v fluctuating
D6 ~28v to 30v fluctuating
D7 ~9v to 12v fluctuating

Thank you again!

 

[merlynski]

I forgot to specify no input signal, input set to Aux, volume to minimum. Those diode measurements should be stable dc voltages. I think we need to step back and have a look at power supplies' voltages.
Measure dc volts on AWR-099:
Pin 17, should be -37vdc:
Pin 24, sb +33vdc:
Pin 23, sb +33vdc:
Pin 22, sb +13vdc:
Emitter of Q5, sb about +17vdc:
Base of Q5, sb about +21.6vdc:
These should all be stable dc voltages, also.
If they are not stable, get a film cap of about 0.1µF to 1µF (not critical), connect it to the tip of your meter probe, meter on ac volts and measure the amount of ac with the other lead of the cap.

 

[vega2k]

Hey there. I finally had a chance to get back on this.

With unit set to AUX, volume all the way down and with Q5 installed (No relay click):

Pin 17, -35.3 vdc stable
Pin 24, +32.4 vdc stable
Pin 23, +32.4 vdc stable
Pin 22, +12.6 vdc stable

From this point however, Q5, Q6 as well as diodes D5, D6, D7 all fluctuating when I tried to measure any leg, especially Q5 and Q6, with Collector leg fluctuating all over the place neg to pos.

I will have to get my hands on the film cap to do the next step you suggested of measuring ac...

What does all this mean???!!! What does all this indicate????!!!! (emotions: worried, frustrated, anxious....)

I expect to get my transistor replacements for Qn delivered later this week. Do you think I should proactively order diodes too?

 

[merlynski]

It acts like leaky transistors imho. Any instability on the cathodes of D5, D6 & D7 will be passed through to Q5, then Q6, keeping C6 discharged and Q7 turned off. That is normal functioning.
Unsolder and lift one end of D5, D6 and D7, then power up. If the relay clicks in then Q5, Q6 and Q7 are most likely fine.
Until the Protection circuit is rebuilt there is nothing more to do, but wait for your parts. The inputs and power supplies are steady according to your measurements.
The diodes rarely fail in this circuit. I always keep some on hand, just in case but if they pass the diode test I would not make a special order.

 

[merlynski]

I would also replace C3 & C4. Here is a couple low impedance ones from Mouser: 232-25YXH330MEFC8X16 or 232-25ZLH330MEFC8X15. FYI, I have not used these but the capacitance is correct, and the voltage is higher than the originals (not a bad thing).

 

[vega2k]

I'm starting to think this thing is possessed! I went to get ready to pull the diode legs as you suggested. For the hell of it, I turn on the unit through the DBT. Relay Clicked! I did nothing to it. SO then I turned it off to reposition it for a better look, tried again - No Click!!. WTF!! Then after wiping my tears and waiting a while, I tried it again and after about 10 seconds, the Relay clicked again, but wait a few more seconds, the relay clicked off. I turned it off....

After a while, I came back and now it is clicking after between 3-6 seconds and staying on... I'm afraid to move the damned thing! Clearly it is not OKAY, but something "clicked" (pun intended)! I will revisit after several hours to check again...

 

[merlynski]

Flaky transistors, have become leaky or noisy with age. This (IMHO) supports that theory.. If it keeps doing this after rebuild then . . .
Go ahead and pull the diodes, if it clicks every time you will know the problem is before the diodes (or maybe the diodes, though I doubt it.)
The SX-750 I was helping with just before yours had a 'Lucy4Pad' problem, an open trace/pad on C4. Look for cold solder joints and/or trace damage.

 

[vega2k]

You confirmed an observation I have had with this Pioneer as far as what appears to be a very delicate board build quality. I have recapped two Marantz power supply units (2270 and 2238B) and I never ran into the types of problems I ran into with the SX-750. Although I have found the SX-750 access to the boards much easier and "user friendly" than the Marantz', the Pio board seems very susceptible to trace lifting, board burning, scratching, trace breaking, etc... Recapping this SX-750 PS & Protect board required almost no disassembly to get to it, but I ended-up "disfiguring" a few areas of the board (around C7 and around C6) because I had to repair damaged traces.

Based on your feedback, last night, I decided to check for continuity on each leg of the caps I replaced. Using my meter, I meticulously touched one probe to the cap leg and the other probe to the nearest next component leg. I found the damaged trace around C6 did not only lift the trace, but also, somehow broke or compromised the trace. My meter continuity beep came on/off as I tested the trace. I ended-up replacing the C6 capacitor, used the new long leg of the new capacitor, bent it and soldered the tip to the next nearest component leg, which was a resistor leg. This bypassed the mess-up trace and ensured a solid connection to the circuit. Once I did that, I have found the relay no longer clicks on/off/on/off and instead stays engaged (knocks on wood). Only once did the relay click off after a long time, but engaged almost immediately. I will be replacing the transistors once I receive them and hope that that resolves the problem.

Thank you so much for the help. I will follow up with a post once I get that done to either (hopefully) close-out the issue/thread or to continue seeking expert help!

 

[vega2k]

..... About a week later, after replacing transistors Q5 and Q6 and putting it all back together with upgraded LEDs (subtle is the key here - No BLUEEEEEE LEDS!!!), it is currently in my main basement set-up. No click/unclick relay at all so far (knock on wood). So the answer to my problem seems to have been trace/pad repairs and replacing leaky transistors! All seems good. Thank you for all of the help and direction!