SX-690 - No Output - Repair Thread - Help & Guidance Requested-Please

PTL-Pioneer

Super Member
Hi All
I have purchased a non-working SX690, same as the SX680 but different dial face (I think).
A really nice looking unit, well built, no idea what they sound like, but i got it to try and fix up without going for the shotgun approach. I know the STK-0039 modules are considered a weak point of this unit.
I just wanted to request some help with this and hopefully with your patience and guidance i can bring this unit back to life. I will then gift it on to a friend who will enjoy it.

So first things first. I took it apart and deoxed all the switches and pots.
Next thing i suppose is to try and get the voltages from each STK and post them here.
To do this, do i just take each reading from the pins on the underside of the board with one lead of my meter connected to chassis of unit, the other on the 0 9 8 and 3 2 1 pins?

One thing i did notice straight away is that the schematic shows 2 fuses beside the stk modules which are not present in my unit?
I would really appreciate some help with this, this will truly be the first foray into actually using some level of diagnostics in fixing a unit. Thanks in advance folks
 

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  • stk fuse.jpg
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Are you looking at the sx-680 or sx-690 schematic? if it is the 680 sch then there maybe more differences that just the dial face.
 
Yes your right, there is a supplement 690 schematic which shows no fuses, thanks.
It does not show the voltages though for the pins, are these the same no matter the unit?
 
Voltages Q1
1 - 0.49 v
2 - 29.2 v
3 - 1 mv
8 - 2.8 mv
9 - 28.9 v
0 - 0.48 v

Q2 voltages
1 - 0.5 v
2 - 29.2 v
3 - 0.1mv
8 - 1.9 mv
9 - 28.9 v
0 - 0.494 v

These were taken with multimeter set to autovolt, using red probe with black connected to chassis, unit on DBT.
Am i doing this right?
 
Am i doing this right?

Yep, your on the right track.

I'm not familiar with the STK-0039, maybe others will chime in.

The pinout appears to be,
0...signal input
1...signal input
2...power rail (-30V)
3...signal output
8...signal output
9...power rail (+30V)

You should redo the measurement on pin 9, -28.9 must be a typo.
The rest don't raise any red flags with me.
 
Not sure those stk modules are original. Usually they read Darlington on the original modules don't they? I've only ever worked on a few pioneer SX models, so I'm no expert, just an observation.
 
I took every fuse out of unit and checked for continuity, all good.
No resistors look burned or anything like that, visually checked only.

The pin voltages for the STKs i have provided contain no typos, that is the measurements that i got, does that mean i have big problem?
Pin voltages are as the numerical order on the STKs in the picture i have provided. I am no expert but it does not seem like anyone was in here before me.
That said they might leave very little footprint if they only replaced the STKs??

Thank you for your help
 
Can you also check the main fuses, FU3, FU4, 5A
Apologies, this was a dumb idea, if fuses were gone you would not have any voltages.
Too early in the morning, need coffee.
Will look at schematic again.
 
Pin 9 is connected to the positive rail, it should be nominally +30V.
You've measured -30V, that is a bit difficult for me to recocile (multiple faults).

Taking it one step at a time, check for +30V at the rectifier ie,
Measure dc voltage at the 2 big filter caps C413, C414 8000uf/50V
You can measure all 4 pins, black probe conned to chassis, you should get
+30V, -30V, 0V ,0V. I'm not familiar with the SX-690 layout, you might be able
to do this from underneath.
Alternatively you can measure at D404 and D405 or R408, look at the schematic
and you will see what I'm after (the +34.5V rail)
 
mbz, do you have a clear copy of the schematics for the 690 ?
The hifi engine copy I have is really hard to read. Gets fuzzy when you expand it and hard to read the placement numbers.
 
Sorry your right pin 9 in both is 29 not -29
OK, voltages to STK appear reasonable.

Maybe you should explain exactly what problem you have and what you have tried eg,
no sound on either channels, same through spkrs and headphone. Tried various inputs
AUX, PHONO, TUNER... No noises/hums/static...
 
input voltages are low to the modules .
is this one of them units that the power supply transistors run hot and de solder themselves ?
 
input voltages are low to the modules .
is this one of them units that the power supply transistors run hot and de solder themselves ?

Funny you mention this.. I found a hotspot on the underside of the pcb at the exact location you mentioned. I assumed someone had gone in there previously and had replaced the Transistor with shoddy solder work.
Now I think of it, what you say makes sense. I suspect the heat actually bubbled the solder to create that shoddy look. I desoldered it and clean with Isopropyl alcohol then re soldered back in. Maybe this would explain the low level hum/buzz. I haven't powered it back up as I have yet to rebuild my DBT. I had to scavange the cord plug sometime ago. Hopefully this week I will have the DBT sorted so i can power up and take voltages as described here.

Before.jpg

BEFORE (ignore the red circle to the left)

Cleaned and re soldered.jpg

AFTER

20170227_063523.jpg after clean.jpg
 
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