Q5 Resistor Replaced, SX-850 still clicking off
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'88Jetta16v
Member
Okay, I'm about to order new micas and thermal paste from Mouser so I can put the output transistors back into the unit and test then test the protection and power supply boards again. But I figured it makes sense to order the parts I need for the power supply board at the same time. I want to make sure I order correctly, since Mouser seems to present multiple versions (usually the last few letters of a part number) of a given transistor or diode.
Are these part numbers the correct option?
Q4: KSA1013: 512-KSA1013YBU
Q6: KSA1013: 512-KSA1013YBU
Are these part numbers the correct option?
Q4: KSA1013: 512-KSA1013YBU
Q6: KSA1013: 512-KSA1013YBU
repo_code
somewhere in the 20th c.
Just a data point. I had an -850 that would randomly toggle the relay off and back on. The power amp circuits were behaving themselves-- constant and low DC offset on both -- so that wasn't the trouble.
The +36.5V supply was stable. Except it would jump up a few 100s of mV when the relay opened. I decided that this was an effect of the relay opening, not the cause. There's less draw on this supply with the relay open.
I ended up replacing all of the transistors on the protection board, which solved it so far (knock on wood.)
I believe it was one of Q1-Q5 that fixed it. I started by replacing Q7 and adding a protection diode for it, but that didn't solve it. I didn't replace Q6 until after the problem had been gone for a while.
It's surprising to me that one of Q1-Q5 caused the trouble. These are not that close to the PSU, they are isolated from voltage spikes that come in on the mains. They're also pretty well isolated from the amp output rails. They don't carry a lot of current and shouldn't get hot, so I would not have expected any of these to fail. Yet at least one failed, I think.
The +36.5V supply was stable. Except it would jump up a few 100s of mV when the relay opened. I decided that this was an effect of the relay opening, not the cause. There's less draw on this supply with the relay open.
I ended up replacing all of the transistors on the protection board, which solved it so far (knock on wood.)
I believe it was one of Q1-Q5 that fixed it. I started by replacing Q7 and adding a protection diode for it, but that didn't solve it. I didn't replace Q6 until after the problem had been gone for a while.
It's surprising to me that one of Q1-Q5 caused the trouble. These are not that close to the PSU, they are isolated from voltage spikes that come in on the mains. They're also pretty well isolated from the amp output rails. They don't carry a lot of current and shouldn't get hot, so I would not have expected any of these to fail. Yet at least one failed, I think.
'88Jetta16v
Member
Ok, I'm finally back to this, unfortunately life has a way of forcing us to concentrate on things other than Pioneer SX-850s sometimes.
I built a dim bulb tester and with the output transistors all testing good, I reinstalled them with new thermal paste and new mica insulators. At that point, the receiver tests the same as always, it plays great until it starts clicking off and on.
Next as TSD and Watthour requested, I tested all the pins on both the Power Supply board and the Protection board, this time making sure not to confuse them. Results are as follows:
Protection Board
1) .04 VDC
2) -13.47 VDC
3) .013 VDC
4) 0 VDC
5).03 VDC
6) .05 VDC
7) .022 VDC
8) .003 VDC
9) 8.55 VDC
10) 36.77 VDC
11) 36.77 VDC
12) 7.53 VAC
Power Supply Board
1) 0 VDC
2) 5.461 VDC
3) 5.461 VDC
4) 13.93 VDC
5) 13.93 VDC
6) 51.32 VDC
7) 51.32 VDC
8) 36.75 VDC
9) 36.75 VDC
10) 36.75 VDC
11) 28.19 VDC
12) 0 VDC
13) -13.47 VDC
14) -50.90 VDC
15) -18.58 VDC
How do the numbers seem?
I built a dim bulb tester and with the output transistors all testing good, I reinstalled them with new thermal paste and new mica insulators. At that point, the receiver tests the same as always, it plays great until it starts clicking off and on.
Next as TSD and Watthour requested, I tested all the pins on both the Power Supply board and the Protection board, this time making sure not to confuse them. Results are as follows:
Protection Board
1) .04 VDC
2) -13.47 VDC
3) .013 VDC
4) 0 VDC
5).03 VDC
6) .05 VDC
7) .022 VDC
8) .003 VDC
9) 8.55 VDC
10) 36.77 VDC
11) 36.77 VDC
12) 7.53 VAC
Power Supply Board
1) 0 VDC
2) 5.461 VDC
3) 5.461 VDC
4) 13.93 VDC
5) 13.93 VDC
6) 51.32 VDC
7) 51.32 VDC
8) 36.75 VDC
9) 36.75 VDC
10) 36.75 VDC
11) 28.19 VDC
12) 0 VDC
13) -13.47 VDC
14) -50.90 VDC
15) -18.58 VDC
How do the numbers seem?
All the voltages look fine, they match the schematics within the tolerances.
I can not see why the relay is cycling if what you are reading are steady voltages. for the relay to turn off,Q7 has to turn off, so q6 has to be on, bringing Q7 base close to ground.
the power amp DC offset voltages are fine
Protection Board
1) .04 VDC
3) .013 VDC
if these voltages above are stable, take it off the dbt. I have a switch in my dbt to bypass the lamp.
The relay is closing? I would think that it should with 36.77-8.55=28.55 volts across its coil.
I can not see why the relay is cycling if what you are reading are steady voltages. for the relay to turn off,Q7 has to turn off, so q6 has to be on, bringing Q7 base close to ground.
the power amp DC offset voltages are fine
Protection Board
1) .04 VDC
3) .013 VDC
if these voltages above are stable, take it off the dbt. I have a switch in my dbt to bypass the lamp.
'88Jetta16v
Member
All the voltages were stable when I took them (the relay wasn't clicking on/off at the time). Maybe it would have been different if the relay was clicking on/off, but that's random and hard to predict. Sorry, I'm not sure what you mean by "take it off the dbt".
do you have it working without the dim bulb tester (dbt)? does the protect relay engage? the relay intermittently, clicks off/on once and a while?
So to summarize, you have rebuilt the power supply. it still does the same problem?
have you checked/adjusted the bias/offset on the power amp pcb? Your offsets look okay, how about bias?
Need to figure out what is causing the protection to trip the relay, issue with the protection ckt, power amp.
Would not hurt to change those 0.22uF ecaps in the protection ckt, use some film caps this time.
So to summarize, you have rebuilt the power supply. it still does the same problem?
have you checked/adjusted the bias/offset on the power amp pcb? Your offsets look okay, how about bias?
Need to figure out what is causing the protection to trip the relay, issue with the protection ckt, power amp.
Would not hurt to change those 0.22uF ecaps in the protection ckt, use some film caps this time.
'88Jetta16v
Member
dbt went right over my head, yikes. Yes, the relay clicks off/on with or without the dim bulb tester hooked up. To summarize, when turning on from cold, the unit plays great for 5 to 10 minutes, then the relay clicks off. It clicks back on, music continues playing. It could be another 5 minutes or 30 seconds until the relay clicks off again. The process repeats. However, I do feel that it becomes more frequent if the volume is higher or the unit has been on for a longer period of time, in which case heat seems to be the common factor. At times, it would reach the point that the relay was clicking off/on almost constantly.
At this point, I have ONLY replaced the Q5 transistor, as advised in a previous thread, which did not improve the issue. I have NOT rebuilt the rest of the power supply board or done anything with the protection board beyond checking the voltages. I did remove all the output transistors and test them (tested out A-OK) and then I reinstalled with new thermal paste and micas.
Happy to check the bias on the power amp pcb, but you'd have to explain how to do that, sorry.
At this point, I have ONLY replaced the Q5 transistor, as advised in a previous thread, which did not improve the issue. I have NOT rebuilt the rest of the power supply board or done anything with the protection board beyond checking the voltages. I did remove all the output transistors and test them (tested out A-OK) and then I reinstalled with new thermal paste and micas.
Happy to check the bias on the power amp pcb, but you'd have to explain how to do that, sorry.
The protection circuit may be doing it's job correctly, there's a whole WORLD of things it could be. STARTING with a bad solder joint somewhere (heat is THAT clue) in either the power supply OR the power amplifier. Bad as in microscopically cracked and hard to find visually - but a POWER OFF wiggle test with the lead will reveal the "give" in a supposedly solid solder joint. Use a sharp instrument as a probe, firmly touch it to the wire sticking through the joint and try to MOVE the wire. Somewhere you will have success and it will move. When that happens resolder the joint with fresh solder and then KEEP GOING... where there's one cracked joint there assuredly are others.
The alternative is to catch it in the act of triggering the protection and figure out WHERE that trigger is coming from - then backtracking it into the misbehaving circuitry.
Now, there is one short cut possible - the transistor that drives the relay. It depends upon the timing of the interruption after the sound cuts out.
HOW does the sound come back, pay close attention to the time that the sound is missing, IS IT THE initial power up delay time? IF it is, it means the protection circuit is doing it's job, if it comes back FASTER, it's the relay drive transistor - which does tend to fail.
protection assembly awm-062
Q7 2SC1384-R
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
extra diodes: 2x 512-1n4004, one for D8, the other goes between pins 9 and 10 (banded end of the diode) of the protection board - to kill the inductive kick (possibly over 60 volts!!) of the 1 watt of magnetic field in the relay coil collapsing when the relay is turned off.
You will see that the replacement is a larger transistor, more robust and can shed heat better.
The leads will be a tight fit in the holes, but it's NOT the hole's fault if they don't fit, the hole has leftover flux residue that clogs it.
Heat or a cleaner (acetone) will dissolve the flux. Or you could poke something through to mechanically clean the holes.
The alternative is to catch it in the act of triggering the protection and figure out WHERE that trigger is coming from - then backtracking it into the misbehaving circuitry.
Now, there is one short cut possible - the transistor that drives the relay. It depends upon the timing of the interruption after the sound cuts out.
HOW does the sound come back, pay close attention to the time that the sound is missing, IS IT THE initial power up delay time? IF it is, it means the protection circuit is doing it's job, if it comes back FASTER, it's the relay drive transistor - which does tend to fail.
protection assembly awm-062
Q7 2SC1384-R
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
extra diodes: 2x 512-1n4004, one for D8, the other goes between pins 9 and 10 (banded end of the diode) of the protection board - to kill the inductive kick (possibly over 60 volts!!) of the 1 watt of magnetic field in the relay coil collapsing when the relay is turned off.
You will see that the replacement is a larger transistor, more robust and can shed heat better.
The leads will be a tight fit in the holes, but it's NOT the hole's fault if they don't fit, the hole has leftover flux residue that clogs it.
Heat or a cleaner (acetone) will dissolve the flux. Or you could poke something through to mechanically clean the holes.
Hello everyone - I just wanted to add my 2 cents to this discussion in the hope it might help someone. I have an SX-1050 that sits around on a shelf most of the time. Once in a while I get nostalgic and want to play it. In the past few years its been working OK as-is (mostly original/un-restored), but it's one of those 'when I have more time I'm going to restore this thing' type of projects..
Anyhow - my protection relay started doing the cha-cha a while ago which is why I stopped using the 1050. Just the other day I brought it down off the shelf to take a look at what might be causing the issue. I have read about how the caps can cause this problem, along with the relay actuation/drive transistors, but in my case it was something different.
It appears that in terms of design, there is some simple 'diode logic' going on with this board that allows more than one kind of failure condition to de-actuate the relay. Using the service manual downloaded from hifiengine.com and a DMM set to DC volts, I checked voltages both at the terminal pins and elsewhere on the protection board to see where the intermittent condition was originating. My DC offsets at the amplifier channel outputs were both very low, on the order of a few mV, and steady, so I was thinking that was not the issue.
In tracing backward from relay driver transistors, I was seeing a shaky/noisy all-over-the-place voltage at the cathode of diode D8 (I believe this is called D5 on the SX-850). This diode is driven by the tied collectors of Q1 and Q2. These appear to be able to pull down through the diode in events of over-current on the output devices.
I thought perhaps there was an issue with the 0.22uF 25V electrolytic caps from base to emitter on one/ both, so I replaced both caps with similar tantalums I had on hand, but this did not help. I then lifted the collector leg of Q1 to isolate the issue but got the same fluctuating voltage. I lifted Q2's collector leg and of course the problem went away because now there was nothing in-circuit at that point. I removed both Q1 and Q2 (2SC869), and replaced them both with some common BC337-16 transistors I had on hand, and the voltage is now steady with no more relay cha-cha.
I guess if there is a moral to this story, it's that it's usually worth spending some time with the schematic and a meter/scope to see what's actually happening during a failure, rather than wholesale replacement of components ('shotgunning'). Granted at this vintage, you might want to eventually replace some old parts anyway (usually caps) so that's why people tend to want to throw a bunch of parts at a repair like this, but it might leave you frustrated when it still doesn't solve the problem.
Anyways, I hope this helps..
Regards,
Dave
There is no such thing as a dumb question when one is new to any thing that he or she is not familar with, there are only dumb people who do not ask questions!!
Jetta16v - Don't know if you're still working on this SX-850 relay issue. But as Polaris26 posted above, just replace Q1 and Q2 (2SC869) on the protection board and this will likely fix your problem. I've seen them fail on numerous Pioneers with this protection circuit. After that, you can rebuild power supply if you want.
