Pioneer SX-9 Where to start, if at all

My manual showed up and I got a good meter.

The DC balance adjusted with VR1 and VR2 measures:
L 5mV
R 0mV

VR3 and VR5 adjust within specs at 56 and 70mV

VR4 and VR6 start at 136mV with both pots fully counterclockwise and only increases with any attempt at adjustment.

I have noticed that the transistors Q1 and Q2 are ECG033(black) and Q5 and Q6 are ECG034(green) while the ones at Q3 and Q4 are 2sc2526(black) and Q7 and Q8 are 2sa1076(green). The replacements (ECG033 and ECG034) are on the heatsink that gets really hot.
 
My manual showed up and I got a good meter.

The DC balance adjusted with VR1 and VR2 measures:
L 5mV
R 0mV

VR3 and VR5 adjust within specs at 56 and 70mV

VR4 and VR6 start at 136mV with both pots fully counterclockwise and only increases with any attempt at adjustment.

I have noticed that the transistors Q1 and Q2 are ECG033(black) and Q5 and Q6 are ECG034(green) while the ones at Q3 and Q4 are 2sc2526(black) and Q7 and Q8 are 2sa1076(green). The replacements (ECG033 and ECG034) are on the heatsink that gets really hot.


what about Q5 and Q6?

The diagnosis is easy, fixing it however, isn't.

The replacements require a lower base to emitter voltage than the originals. Which causes higher idle current.

I am surprised that I couldn't reference the ecg033, the speed is important.
It is a rectangular case, correct? Similar to the originals?

Could you post pictures of them?

I would need a schematic to try to see if the drive voltages can be turned lower with component changes. I haven't been able to find that, either.
 
Mark; I Have a xref for ECG from MOYER Electronics. It shows the ECG's as ECG33 and ECG34.

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Using the orginal part #'s (2sa1076 & 2sc2526), The NTE so called "equivalent" would be NTE 92 and 93. :tears: (see attached .pdf)

WEEBER! DO NOT USE THE ABOVE AS REPLACEMENTS! They were culled to verify existing parts in your unit. Once Mark has gone thru the manual and "reverse engineered" things, he'll come up with a solution to the problem parts. Patience is a BIG VIRTUE right now.

Larry
 

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From the service manual:
Q1, Q2, Q3, &Q4 should be 2SC2526
uploadfromtaptalk1405003554596.jpg
Q5, Q6, Q7, & Q8 should be 2SA1076
uploadfromtaptalk1405003588371.jpg

But here someone has replaced:
Q1 & Q2 with ECG33
uploadfromtaptalk1405003603952.jpg
Q5 & Q6 with ECG34
uploadfromtaptalk1405003619949.jpg

They look exactly the same and are physically the same size and shape.

MTF: I have a really nice manual from Rick, I can try to send you some good scans of whatever diagrams you need. If those won't work, I can send the original for you to look over and return after.

Larryderouin: you mean DON'T Use the NTE products, correct? I've heard they're not good.

I don't think these transistors are faulty, the amp works and plays music, but I suspect if it played for a long time bad things would happen. I've not used it for more than about 5 minutes.

Here's a picture of the bottom of the power supply board, specifically some hit looking spots. Do any of the Solders look like stuff had been replaced here? I will check for cracked solder joints too.
uploadfromtaptalk1405004285260.jpg

Sent from my Z10 using Tapatalk
 
all we will be doing is trying to reduce the base voltage of the output transistors a smidgen. If possible, on that channel.

Are you sure that the idle current pots were all turned all the way down?

Second - check their resistance (with the power off)

third - we check the voltages at the pots on operation, unfortunately we need to dial down the other channel to see if there are significant differences in the starting points for the adjustments - something else may be restricting the adjustment range.

Once we are sure that other than the output transistors, everything else is reasonably similar, then we start looking for "mods". Perhaps reducing the 7mA current delivered by the current source to the bias diodes slightly will get us the breathing room we need.

The NTE parts are there, so we try to use them, they DO have the appropriate cases.

otherwise we try Sanken 2sa1216 / 2sc2922 from ampslabs.com at 40 bucks for a set of 4.as long as we can get them to physically fit.

When you have scans ready to email, PM me and I'll send you my email address.
Scan the schematic as well as the board layout, both in rather high resolution.

Then I will be able to start giving you better directions on what to measure to figure this thing out. Like is that 7mA current high?
The current through the thermal bias diodes directly affects the voltage across the diodes, and the current is controlled by a current source, and THAT is controlled by a transistor and a few resistors. The resistors could have drifted in value, the transistor damaged by heat (THAT transistor tends to run HOT) or several other things could have happened. I am making a BUNCH of assumptions, that will change as I get the schematic.

We BOTH need the manual, or a very good copy. You might consider getting a second one sent to me.
 
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Yes that's what i meant. Don't use the NTE's as replacements unless there is absolutely no replacement to be had in any case configuration. Mark and Echowars have been doing this for ages and their replacements tolerances/specs are way better than anything NTE could even dream of. It might get pricey at times with the higher ended units, but when done they are damn near nuke proof!!!

Mainly I posted that for clarification of the ECG to NTE #'s for Mark.

Larry
 
You can always swap the original outputs and ecg replacements to see if the problem moves to the other channel with them. OR NOT!!! (as in the problem stays put..)
 
Yes. The pots were turned all the way down counterclockwise.

The resistance on each pot (using the ohm meter) from one side is the same as the pot on the other side with VR5 & VR6. That is they start at zero and go up as they are turned to 43000 on VR5 and 37000 on VR6.

VR3 goes from 0.4 to 50 and VR4 ends at 50 too, but all the way clockwise gives anywhere from 12 to 38 to start and then drops to about 5 with a tiny bit of movement. The value never goes lower than 5 though.

I'm not sure how to measure the voltage at the pots. I moved them all counterclockwise and put a probe on each side, but they all read 0 volts (with unit on). Should I be reading from different points?

I working on making copies of the schematics. I'll pm you when I've got that done. I'll just send you the original manual.
 
Well there goes that

I consulted with my father in law who knows about electronics and he said to test the voltage at the pots, one lead would be on ground and the other on one leg of the pot.

So I clipped the negative lead to the chassis and plugged the receiver in. I hadn't turned on the DMM yet and the other lead was no where near the amp, but when I pressed the power button sparked flames and smoke fizzled out from the power amp board. I freaked out and yanked the cord out of the wall.

Could it have done this on its own? Did I do this? Nothing was touching anything other than a clip on the chassis.

I guess I'll take it apart and see which components are crispy. Most likely this will have caused a chain reaction of fried components, am I right?
 
Yes a DC amplifier design tends to fry a lot of parts. I would guess you accidentally shorted something.
 
Just when the experts had started down the path of providing a solution....

sorry, man. MarktheFixer and larryderouin could have steered ya right.

Best of luck.
 
Who would have thought two tiny resistors could make such a fireball!

e3yva8yb.jpg

e8ezuby5.jpg


Sent from my Z10 using Tapatalk
 
The hot spots are on the power supply. These are on the amp board

Sent from my Z10 using Tapatalk
 
I think I see where I went wrong. Before I turned it on to test the voltage, I made sure that all the adjustment pots where turned all the way counterclockwise. But I see now that I missed VR5 which was turned all the way clockwise.

Could that have caused this?
 
Yes, that will certainly let out the magic smoke. You should never mess with the pots on a working amplifier. If you must, just trim the values a little. If offset is under 30 MV you are better off just leaving it as is. just out of curiosity why did you do that? (turn them to the extreme of rotation)
 
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Oh boy... bloooooiiiiieeeeeeeeeeeeeeeeeee............ That's NOT good.

Look at that board, there is a number on it that I can't quite read, if it is NOT awh-097 you are going to NEED to buy a Service manual from Rick at stereomanuals.com - that kind of damage can't be swag'd.

The resistors are most likely 100 and 200 ohms voltage summing resistors for the idle current measuring point, and THAT means that the white square resistor is also blown to hell. And probably because shorted output transistors took it out. The little resistors connect some places that are only millivolts apart, UNTIL that white resistor blows, then they can have a hundred or more volts across them because the outputs short (outputs short first - that blows the white resistor, which then vaporizes the two little ones). Sometimes the cascade continues, and invisibly crosses over to the other channel via the protection system.

As far as the amplifier, it can be repaired, but not easily. New outputs, lot of other transistors, some resistors and diodes. Blown NSA amps are always difficult and finicky. Basically because it is controlling all that power. But coupled with the dynamic power circuitry, it may NOT be a DIY effort. That adds a whole new dimension of damage to the overload.

May have to drill and possibly tap mounting holes for replacement transistors, depending upon the fit.
 
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Wow. If it's that bad it may not be worth me continuing. On the other hand lots of learning could be had.

Do you think that pot turned all the way clockwise did this?

Also, forgive my innocence, but the protection circuit keeps the voltage away from the output resistors until it clicks, or please set me straight. I ask because this nastiness happened the instant I pressed the power button. Way before the relay clicked. Or in situations like this it all goes bad regardless?
 
turning the pots to their extremes did blow the channel, never do that. If you are going to continue the repair the first thing is to restore the pots to their original settings. You may kill the other channels as well during future power up cycles. The protection circuit protects your speakers. It does not prevent the amp from starting. There is tremendous voltage and current in the power supply, When applied to an amp with the operating parameters unbalanced the destruction occurs in milliseconds.
 
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