Pioneer sx-650 right channel not working.

L

Lucaslz

New Member
Hello from Vienna, Austria. I pulled a sx-650 out of storage to fix up for a friend. I cannot recall when or where I picked it up but unfortunately i immediately started to regret my promise to my friend as the back connection panel looked very rusted and scratched up and the speaker connectors were gone, in its place a common plastic wire connector. I salvaged some speaker connectors from another pioneer donor and assembled them in the 650. I then decided to test the unit, (should have used a bulb current limiter but didn‘t). It turned on, relais clicked, but I only got sound out of the left channel and the lights flickered, (symptom of carbonized power switch). So I took off the bottom and front panels and removed the switch (luckily only held in with metal clips and not riveted), cleaned it thoroughly, replaced the elkos in the preamp board, checked the speaker selector switch and wiring to the speaker junction, gave all the other switches a dose of deoxit and put it back together. It looked okay inside, no obvious damage, just dusty. I tested again but this time with my bulb limiter. First test with a 25w bulb didn’t give any satisfactory results as the relais just clicked on and off. I then tried a 60w bulb and this time the bulb went dim until the relais clicked in, then it got very bright indicating a short circuit. Some sound only from left channel, nothing on right channel. The sound seemed to come on and off (maybe an oscillation) but the relais remained on and the light bulb remained bright.
I’m not sure what to do next, but I think replacing all the elkos and checking the other components on the GWR101 and GWH101 boards seems like a good idea. I am of course praying that the power ic’s (SP-40w) are still okay but I’m not sure how to check them and I don’t have any spares. I figure if I renew and check everything else first then I can test the sp-40w’s properly and replace them if necessary toward the end of the project albeit with something else since the sp40-w is not available anymore. Does anybody have any tips or advice on how I should proceed and does anybody have a BOM list of replacement parts or equivalents which I will be ordering (probably from mouser If they have everything I need). I would greatly appreciate any help offered.
many thanks,
Lucas
 
Register to hide this ad
You should not try to run the amps on the DBT. The bright bulb is the amp’s starving for current.
No volume when using the DBT.
Set the controls for a nominal condition and volume to min. 60 watt lamp is good. If it’s dim when powering on then you could check for DC Balance. Checking for any bias, you will see a lower reading due to the DBT. Only adjust it when on full line power. Only use the volume when on full power.
If the DBT stays dim your go to go to full line power and complete your checks.
 
@zebulon1 Thank you for the explanation, however the bulb remains bright after the relais clicks, so that would indicate that there is a short circuit somewhere, or? If the relais works that means the dc offset is within acceptable range. Also there are no adjustments for dc balance or bias on the sx-650.
I think I will pull out the sp40w’s and bridge pins 2, 4 and 6 on the board with some resistors to measure the voltages on pin 4. If the value there is close to 0vdc then the Sp40w is bad, if higher than 0.05vdc then the problem is somewhere else. At least that it what I have read in this post; https://audiokarma.org/forums/index.php?threads/frustrating-sx-650.937005/#post-14271732
 
My post was a general practice post. Was not near any good reference.
Check all the fuses with your meter.
I am looking at a blurry PDF now and see the STK's and amp circuits.
I would desolder the modules one at a time, install 1K resistors between pins 1-3 & 8-0. Give it another DBT test and check DC voltage readings on all the pins.
Something is weird. Solder bridge(?). Probably the STK's but eliminate them for now.
Double check your work on the preamp circuit.
You have to start somewhere.
 
You have to start somewhere Is true enough. You say I should connect resistors btwn pins 1-3 & 8-0, merlinsky suggested in the aforementioned thread to connect resistors btwn 2-4 & 4-6 on the pcb board to measure results. This of course confuses me a bit but I take it that both methods provide some useful results. What dc voltages am I looking for on those pins?
 
Pins 2 & 6 +- 1.2V with STK in circuit. Voltage will be higher with jumpers (5-9V? depending on resistor values) and STK pulled.

Pin 4 should be less than 50mv. Relay is engaging so there doesn't seem to be excessive DC offset.

+36V pin1. -36V pin 5.

Test on DBT with no load. Expect voltages to be somewhat lower on DBT.
 
Last edited:
I pulled out both of the SP-40w´s and it looks like the right channel module is toast as I measured continuity between pin 1 and pin 2 on that module. There is also the remnants of black soot on that area. I haven’t had any time to do further measurements but will continue after the weekend. In the meantime I will need to find another module. Doesn’t look like there is anything available in Europe. I will keep looking.
 
So, I have ordered some nos sp40w‘s from fleabay in the US. In the meantime with the sp40w’s pulled, i soldered 330ohm resistors btwn pin
2-4 and 6-4 on the pcb. I am assuming that pin 2 is next to the 36v pin 1 as on the schematic. However I’m getting the same readings on both left and right channels. All measurements done without DBT and without load.
pin 2 left = 32.11vdc
pin 4 left = 2.45vdc
pin 6 left = -12.85vdc
pin 2 right = 32.11vdc
pin 4 right = 2.41vdc
pin 6 right = -12.9vdc
According to Merlynsky and others, pin 4 should be 50mv or less, so this doesn’t look good. What about the other values?
pin 1 left = 37.44vdc
pin 5 left = -37.3vdc
pin 1 right = 37.35vdc
pin 5 right = -37.45vdc
what should I test next?
 
Oops, it looks like I will need to redo those measurements. I had 330k´s In there instead of 330 Ohms!
I thought something didn’t seem right. I hope I didn’t damage anything else in the process.
The readings are jumping around a lot, things seem to settle but after less than 2 seconds there is a jump, then the voltages again start to slowly settle on a value, then jump again.
New measurements;
Pin 2 left 1.825vdc after 2 seconds jump to 4 or 5 volts then immediately lower than 1.8 and climbing.
pin 4 left 56.6mv then jumps to >400mv then immediately goes to Minus then climbs back to 56.6
pin 6 left -1.714vdc then jumps to positive 3v back to minus 2 then slowly back to -1.7 before jumping again.
pin 2 right 1.9vdc jumps to 4.8-5.4v then try’s to settle again to 1.9 before jumping again.
pin 4 right 154.5mv then jumps to Minus then plus 1.2vdc then settles again to 154mv before jumping again.
pin 6 right -1.592vdc then jumps to -3.5v etc.

pin 1 left. 37.2vdc steady, no jumping
pin 3 left. -1.1vdc slowly climbing
pin 5 left. -37.48vdc slight fluctuation
pin 7 left 1.5vdc slowly climbing

pin 1 right. 37.15vdc slight fluctuation
pin 3 right -1vdc slowly climbing into minus
pin 5 right. -37.6 slight fluctuation
pin 7 right 1vdc and slowly climbing

I will order those KSA992‘s and a transistor tester to get matched pairs and recap everything on those boards.
 
You must log in or register to reply here.
Back
Top Bottom