Pioneer SX-580 No Sound

[mscottdoran]

Thanks brother, I just found an open resistor R401!

I checked the ac coming off tap 11 of the transformer, it reads 38 vac.
After diode D401 I was getting 53 vdc which goes to one side of R401, the other side of R401 read only 1.8 vdc. Checked across R401 with meter on ohms and power off and it reads open (luckily no resistance in parallel to confuse me).

I'll have to find a replacement and solder a new one in and then go from there.

Thanks again to all who chimed in. It's hard to know where to begin without any experience.

That may not be the only failed component, so I will report back. It will probably be another week though.

 

[mscottdoran]

Am I right in reading the schematic that R401 is a 33 ohm 1/4 watt resistor?

 

[Watthour]

The parts list appears to identify it at a ¼W, but in this position I don't believe it is intended to be a current limiter/safety fuse, so increasing the wattage to ½W shouldn't be a problem. It is only supposed to carry 26mA, but there IS a 220µF capacitor after it in the circuit, so the charging current on unit power-up may be a bit of a strain.

Speaking of that, it might be helpful to check that cap (C404) and the one upstream at least for shorting.

Also, if you are intending to order parts it may be worthwhile to add a few other items to your order, such as common fuses, replacements for the potentially troublesome 2SA725s in the phono preamp, various other suspect caps, and whatever else might be convenient to soften the blow from the shipping cost.

 

[markthefixer]

Well, the +41.7v power feed may have an inordinate power draw. So there is a safety catch, R401....

R401 33 ohms (orange orange black gold) 1/4 watt is intended to act like a fuse, to pop when there is inordinate power draw.
The schematic calls for a draw of 26mA.
87 mA is 1/4 watt with a 33 ohm resistor, more current than this will destroy R401.

R401 is described as a RF 1/4 ps xxx J resistor meaning it is a fusible resistor.

for now we will just use a metal film resistor (mouser.com) 660-MF1/4LCT52R330J to troubleshoot
but it should really end up being a (mouser.com) 603-FRM-25JT-52-33R when everything is done.

R401 could have been "tired" and let go, or it could have been doing it's job.

So we trace the path where the excess current could have flowed. And the components blocking the excess current from flowing.

Check R348 (near the function switch) 4.7k yellow violet red gold (to that 13v zener diode D309)
(each with one leg lifted)
If there was excessive current, R348 4.7k yellow violet red gold would have blocked the current flow and been somewhat damaged (darkened) so it is less likely to be involved

Check R347 (edge of the board NEAR pin 14) 100 ohms brown black brown gold
if R347 100 ohms was in the way of this excess current, poof.... or it was racing R401 to GO poof and is damaged.
BUT only C335 could have allowed excess current to flow, the only other exits from that node are R311 and R312 and at 2.2k a damaged module wouldn't be able to cause that much destruction.



There is a jumper behind the ribbon cable behind the TAPE MONITOR switch, this jumper when opened will isolate the +41.7 volt feed from the circuits below that I discuss: the muting circuit and the phono amp

The +41.7 volts goes to the phono amps, which have very untrustworthy 2sa725 transistors in them, and if one fails, a 10v capacitor (c209 or c210) would subjected to voltages far beyond it's rating, it would fail shorted and thus pull the excessive current.

There are other parts that I am not as concerned about, that by their very nature don't usually fail shorted, and would block excessive current flows:
R507 220k part of the muting circuit
the rest below are part of the phono amp as well.
c220 0.047uf part
r213, r214 680 ohms
r211, r212 18k
r227 56k

Thus, all the gobbletygook above (that some can pursue avidly) says that either:
a shorted C335 that would stress or destroy R347
or
one of the two 2sa725's (Q203, Q204) in the phono amp failing (which they tend to do with distressing regularity) could short out their associated C209 or c210
or
a just plain tired r401 33 ohms

And I located a jumper wire that can be opened to isolate the section I suspect is responsible, letting the power amps work when current flows through the r401 gap.

Because the muting circuit may not function with this jumper open, the partial test can be injecting hum with your wetted finger into pins 48 (left channel) and 50 (right channel) to confirm the power amplifier section's operation.

By the way, a quick test could be to set your meter to current, in a 2 amp range, and touch the probes to each side of R401, bridging it allowing current to flow while measuring that current. Worst case, a high current reading and other defective components could be finished off in a puff of smoke, or you might get a reasonable reading (tired r401).
Then if there is a high current draw you could cut that jumper I mentioned, and try again to see if the current draw goes to normal.

As we troubleshoot a possibly defective phono amp section, we can bridge THAT cut jumper with the meter to power up the section and test it's current draw.

 

[Watthour]

R401 is described as a RF 1/4 ps xxx J resistor meaning it is a fusible resistor.

THAT is a very useful (and appreciated) tidbit about which I previously did not know.

 

[mscottdoran]

Re: MTF,

Good info which will probably save hours of work. I will check those components as well, as you advise.

Do you happen to have the mouser.com part numbers available for the common failure components? One shipment would make more sense for me.

 

[markthefixer]

one shipment makes sense, but it will require patience gathering data. you are the trailblazer for this model's recaqp? It isn't in the "list of lists"... nor do I have any work in progress (yet) on it...

2sa725's 2sa726's get ksa992's
the opposite polarity ones get ksc1845

all cssa caps come out for sure, all electrolytics come out during recap.

not hard or expensive.

 

[mscottdoran]

By the way, a quick test could be to set your meter to current, in a 2 amp range, and touch the probes to each side of R401, bridging it allowing current to flow while measuring that current. Worst case, a high current reading and other defective components could be finished off in a puff of smoke, or you might get a reasonable reading (tired r401).

So, following the procedure you laid out in the above quote, with my meter on dc amps, bridging the open resistor R401, my meter stabilizes at 0.027amps, and the receiver works. So, looks like a tired R401.

I used the MIN MAX function on the meter and read an inrush current draw of 0.121amps dc (but that lasts less than a second).

Is the inrush current anything to be concerned about, or just the stable current?

In the meantime I will gather the parts for the recaqp.

Thanks, Mark the Fixer-you are a troubleshooting badass!

 

[markthefixer]

inrush is not a concern. just the operating current.

Glad there doesn't seem to be complications. Sad because now recap info needed sooner...

Sorry you're a sx-580 recap/renewal trailblazer... instead of having a turnkey list...

some of the other guys can help too, but you'll want to publish the list here, then WAIT for us to check it before actually ordering.

tip - visually verify unit versus list before ordering, there's ALWAYS one damn cap that holds up the works and gives the shippers more business.

 

[Chuckfalcon]

Hi guys, today I noticed an issue with my Pioneer SX-580. In mono mode, audio comes out of both speakers, but when I switch to stereo, audio only comes out of the right, and its only sounds that are on the right side of the recording. For example, on some songs, the guitar solo doesn't happen where it should, you just hear the backing band.

I tried different cables and different speakers and headphones and I get the same result. No audio from the left speaker but if you turn it up REALLY loud, you hear lots of hum and a little audio.

I took it apart this morning and one of the 2 6800uf 35v caps has a huge bubble on it. I ordered replacement for the both of them but I am not sure if this is THEE problem that is associated with the left speaker.

Anyone have any ideas on what it could be?

Thanks,
Chuck

 

[dlucy]

Did a recap and replace-the-transistors list result from all this? I've just scored a $25 SX-580 and it'll be the next project. I'll continue the list if there isn't one ready-to-go.

 

[slayer44]

FYI...I have a perfect working 580. If anyone needs me to pull some voltages from it, I can. I know specs from schematics can vary a little.

 

[slayer44]

Another FYI...The only issue I ever had with mine was sound crackling in and out that sounded like a bad cap value. I bought all the parts to do an overhaul and one day I pushed on the board in a few places and the sound would clear up. Come to find out, the screws that ground the board (underneath) to the chassis were loose! tightened and good as new. Just might save some major work for someone.

 

[slayer44]

Did you ever resolve this amps issues?

 

[richinnc]

I just got finished with an SX-580 and found the same issue. Replaced R401 and it's back in service sounding great, however I'll be checking downstream from the resistor to make sure there aren't further issues that caused the resistor to blow. I suspect it may have just been tired as was the case with another one I fixed last year. BTW, this is an excellent thread and I'm sure it will be very helpful to a lot of hobbyists and even some seasoned techs. I came across it because I wanted to see if I was dealing with a common problem on the SX-580's.

 

[dlucy]

all cssa caps come out for sure, all electrolytics come out during recap.

I've started recap prep for my SX-580 and I don't see any CSSA caps in the schematic's parts listing. I also don't see any robin-egg-blue Sanyo tantalums. The schematic seems kinda short on parts listings... or the layout is baffling me and they are hidden somewhere.

What was the reasoning behind always replacing CSSA's? (So I can apply that same reasoning to whatever is in this model.)

 

[H-daddy]

Thanks brother, I just found an open resistor R401!

I checked the ac coming off tap 11 of the transformer, it reads 38 vac.
After diode D401 I was getting 53 vdc which goes to one side of R401, the other side of R401 read only 1.8 vdc. Checked across R401 with meter on ohms and power off and it reads open (luckily no resistance in parallel to confuse me).

I'll have to find a replacement and solder a new one in and then go from there.

Thanks again to all who chimed in. It's hard to know where to begin without any experience.

That may not be the only failed component, so I will report back. It will probably be another week though.

I know it is 2 years later BUT I have the same issue with my receiver BUT I cannot figure out from the crappy schematic where R401 is in the power supply circuit. Does anyone have a source for a schematic I can read more easily or maybe even a schematic of just the power supply part? Thanks!

 

[dlucy]

Do these help?

 

[H-daddy]

Yes! Thanks so much. I was using the images from the service manual. These are soooooo much better.

 

[wobbie]

Well, the +41.7v power feed may have an inordinate power draw. So there is a safety catch, R401....

R401 33 ohms (orange orange black gold) 1/4 watt is intended to act like a fuse, to pop when there is inordinate power draw.
The schematic calls for a draw of 26mA.
87 mA is 1/4 watt with a 33 ohm resistor, more current than this will destroy R401.

Thanks so much for that.

My 580 failed years ago with the 100 ohm R318. Lately my replacement got tired and the same channel went dirty. Replaced and worked for a bit and then went completely quiet. Enter R401.

Thanks for your info. I likely would not have bothered digging deeper if I hadn't found this post.

Regards.