Suggested first step - No sound SX-580

onanboy

New Member
First time poster so be gentle. I read the rules and even though it said not to make your first post be begging for help, I am rudely ignoring it. I did spend a few days scouring the posts for similar problems to mine first.

Here goes..... I have an SX-580 in my garage that I use for music in the garage and backyard. It has worked fine until a few days ago when the music just stopped. The lights work, the tuner works, all of the fuses (four that I saw) are still good. There is no sound on the speaker outputs or from the headphone jack. Everything looks pretty good inside the chassis that I can see.

First.....which Deoxit should I get. I am sure that should be my first or second purchase.

Second....if I really want to repair this thing is ordering a service manual (which I assume has a schematic) mandatory?

Third which components should I automatically change in order to prevent future failures after this one is fixed (i.e. Darlingtons, STKs, caps)?

Any help would be appreciated.

Paul in Racine, WI :scratch2:
 
Sounds (no pun intended) like the regulated power supply board would be the place to start. Probably a bad transistor. Thats what I'd look for first. Of coarse the first thing would really be to get a competant tech here on AK to hold my hand while I tried to trouble shoot the issue. Good luck and welcome to AK.

Jason
 
The SX-780's are notorious for cold (loose, broken) solder joimts on a couple of transistors. Might be the case with the 580. Maybe try doing a search using the 780 to get some guidance. If the relay doesn't click, it could be the problem. Welcome aboard
 
Strawman, I was just going to suggest that. I just repaired my 680 by simply resodering. Easy and slick.

Onanboy, check out all the soder around the regulated power supply board. See what you can find there...

after of course, you get some deoxit at partsexpress.com.

cheers.
 
These guys are steering you in the right direction. On the regulated power supply board you will see some transistors with metal tabs on them. Some or all of these will have little aluminum heatsinks attached. On the solder side of the board, inspect the solder joints on these transistors. Resolder any that are not shiny, and any that have a dark ring around the transistor lead. If this doesn't fix it, it could be a blown output transistor or module. If there are black plastic packages screwed to the large heatsink that say something like STK-0050 on them, those are output modules. Close to the modules will be 2 air core coils. Measure the voltage from each coil to ground. If it's more than 100mV, the output is blown.
 
Sounds about right, and IF you're in a hurry radio shack has a somewhat expensive deoxit - progold double pack that will get you going for the weekend.
It's enough for one unit, remember a little goes a long way...

We are of course assuming you have a DMM and adequate soldering equipment/skills. Bad solder joints are shy suckers sometimes, a sharp pointed pick can help, by seeing if any movement can be induced in a supposedly secure component lead.

As far as preventative replacement maintenence philosophy, opinions may vary, mine is if it ain't broke, dont break it...

It would be prudent to get a manual (cd manuals can be shared), if these first steps don't fix it, and if you have a digital camera that you can post pictures with, that could also help.

But the biggest question in my mind is whether or not the 580 HAS a protection relay.

EDIT: It probably doesn't, the sx-680 does NOT have one , so it is reasonable to assume the lower model number doesn't either.

The power supplies on this unit are simple and direct, if the fuses TEST ok, (looks CAN be decieving, especially on older fuses) the power supply area is the only commonality that can kill the sound on both channels at the same time on a unit without a protection relay.

The power supply area is probably at the back of the pc board and on the same side as the speaker select switches on the front panel.

PM me with your email address and I'll send you 4 500k .jpg's that have the schematic and pc board layouts for the sx-680. That should help...
 
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Great ideas one and all. Yes I do have a dmm and I can do soldering. I have limited circuit knowledge (limited in audio at least). I think I may do the picture thing this weekend and I may stop by my RS for Deoxit. I don't mind the prices at partsexpress but the shipping is almost as much as the spray.

If I can get this thing working I may even try to refoam my AR-8s pretty soon. These forums may just have given me the intiative that I needed.

Will try to report back with any successes.

Thanks,
Paul
 
I advise purchasing a decent soldering iron and a digital multimeter. These two items will make your life much simpler.

As others have said, resolder the regulators on the power supply board. For a number of years, Pioneer underdesigned their power supplies. Easily corrrectable though.

Treat switches and controls with Caig DeoxIT D5. Put a couple of drops of D5 on each of the moving contacts at the center of the multi-gang tuning capacitor.

Enjoy.

Fred Longworth
StereoTech Classic Audio Repair
http://www.repairaudio.com
 
I just checked my 580, I don't see a relay unless it's under the tuner board.
Any progress?
 
First Pass

Took my first pass at the receiver. Removed top and bottom. From the top there are only wire wrap connections and from the bottom I can access the solder points.

I am not really sure what the power supply board is. I am assuming the ATT-510 is a transformer of some kind. Maybe someone can point out where the transistors with the mini heat sinks are. As far as I could see the solder points were still pretty good.

Sorry to be ignorant. I should know more than I do.
I have pictures that can be referenced.
 

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onanboy said:
Took my first pass at the receiver. Removed top and bottom. From the top there are only wire wrap connections and from the bottom I can access the solder points.

I am not really sure what the power supply board is. I am assuming the ATT-510 is a transformer of some kind. Maybe someone can point out where the transistors with the mini heat sinks are. As far as I could see the solder points were still pretty good.

Sorry to be ignorant. I should know more than I do.
I have pictures that can be referenced.

Hello,
First, don't apoligize for being ignorant...you are learning just as I am.

Ok, look at the attached picture. I took the one you took, and circled three items you should check soldering on. The two black long things are the transistors with the heatsinks. Check every pin on them from the underside. Also, just because it was the problem on my 680, check the capacitor solder on the one I circled. That was where my problem was.

Enjoy, and keep us updated.
Cheers.

Edit:
That picture didn't turn out that great. If you can't see the information, check out the second one, I think it might be better.
 

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I hate to say it but Fernzee has you looking in the wrong place... he has circled TWO integrated circuits... the pa3001 fm if chip which IS working because you say in your first post that the tuner works... without sound the only way you can know that is by the tuning meter, which is part of the pa3001 's circuits...
The second integrated circuit is a pa1001 stereo decoder chip.... also NOT the problem.

The two x'd out blue circles are what fernzee outlined. The yellow double circled bullseye is the transistor that is the "power supply" you need to be looking at .

I base this on ALL the previous posts which I have CAREFULLY RE-READ....
AND then gone through the 680's schematic with a FINE TOOTH COMB!!

There are two sources of power from that transformer you have mentioned, they come in on the two RED leads and the two GREEN leads.

The RED leads supply the OUTPUTS of the power amplifier and the power to run the TUNING circuits which comes through the heatsinked regulator transistor Q401, with the double yellow circles,mounted on a chunk of angled aluminum in the picture. Thus if the tuning is working , meaning if the tuning meter moves, the power amp has it's juice to BLAST.....

********** BUT ************

The amplifier needs OTHER REGULATED POWER... that comes in on the GREEN wires from the transformer. BE SURE that BOTH fuses connected to the green wires are OK, take them out and ohm them out to near zero ohms...
There is a HIDDEN transistor near the double yellow circled Q401 . this is where to look for bad solder joints, and where 3 voltage measurements need to be taken. This supplies 45 volts to the amplifier circuits... without it they're dead...
*********** here's ANOTHER "BUT" ***************
The green wires also supply a Negative 29.5 volts that is directed to a power on muting circuit !!! weird, but since there's no protection circuit, they put this in so that there is no "thump"...
What does this mean?? that the 45 volt power supply could ok and there could STILL be no sound. but with the volume WAYYY up you MIGHT hear something...

BOTTOM LINE:
1) check those fuses, out of circuit.
2) check the solder joints around that transistor with the aluminum angle attached
3) get ready to measure a few voltages.
 

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The sinked trannie Q-401 should read approx. B=14.3V, C=30.0V,E=13.6V. The three leads from Q-401 make up a triangle on the foil side The transistor refered to earlier, Q-402 resides nearby in the power supply, by the 4 smaller electroylytic caps, it is unsinked, it should have readings around B=42.3V, C=44.7V, E=41.7V. it's leads line up in a straight line. CC
 
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Thanks both of you guys. I will make the checks and report back.

Besides checking the solder joints, how would I go about checking the Q402 transistor? I am assuming that it is open while unpowered so the checks need to be done while the receiver is on its side and the bottom plate is removed. What points should yield the 45 Volts?
 
The big transistor on the heatsink will have 13.6 volts, 14.2 volts and 30 volts, it is the transistor for the tuner's power supply on the heatsink... This means that the 45 volts is being regulated by a smaller transistor that is NOT mounted to a heatsink, but is within a few inches of it and NOT visible on the picture,it is probably under those black wires between the brown disk shaped thing covered with a translucent plastic insulator and the 3 capacitors ( 3 tall black plastic insulated "cans") next to the heat sink.

On the 680 the little "hidden" transistor has 50.4 volts on the collector, 45.6 volts on the base and 45 volts on the emitter. Your mileage may vary...


Try to reconcile the layout diagrams I emailed you, with the rough parts placement on your unit, as they ARE different models. If we dig much deeper we will probably need to get the correct manual for the unit, probably through ebay, hopefully on CD, so that I can make a copy on my hard drive.

EDIT: BTW charlie had it right, but I didn't see his post till just now, after I had gone back to edit my previous post, the power transistor IS the TUNER power supply regulator and is WORKING. Credit where credit is due...
 
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you check the individual leads of each transistor to ground. Hook your black lead of your DMM to the phono ground post or a good ground, then very carefully with the power on probe with the other (red) lead each solder joint that is involved in the transistor (3 in this case) from the foil side, the underside. If you have a real steady hand this can be done from the top side, but I dont recommend you try it that way, very easy to short something out. You claim to have a DMM you should get readings approx. what I posted in an earlier thread. I don't recall if you mentioned in earlier threads how advanced your work area and tools are, does your DMM have a diode checker, that feature is very valuable and helpful. You may also need a solder iron and either a solder sucker or solder wick to dislodge the different componants that you may wish to check. The SX-580 is a nice little low powered reciever. I have two and they are not to bad to work on. good luck I think Mark has you on the right track now CC
 
It's a good idea to wrap a piece of electrical tape around your meter probe so ony the very tip is exposed. This helps to keep you from accidentally slipping and shorting something out.
 
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