Another SX-1250 needing help

[vwap]

I have a Pioneer SX-1250, and like many others around here, it needs help

When I initially got it, it worked intermittenly -- the audio would come in after the first relay click, then about a minute or two later, cut out. Subsequent tries got shorter and shorter, until audio wouldn't come on at all. The left heatsink was quite a bit warmer than the right every time, so I thought perhaps this was a heat issue (but not ambient heat, as it was pretty cold in my place...)

One day it somehow started working with no problems. A week later, it was just as inexplicable when the unit failed to power on.

I finally had a chance to look under the cover, and checked the fuses. The five glass fuses seem fine. The ceramic 12A 250V 3AB seemed blown. I went to the local electronics store, and they sold me a pack of Littelfuse 12A 32V 3AB fuses, mentioning that in the 3AB format, there's only one 12A, so regardless of what my fuse said (he wouldn't even look at the fuse I had), the voltage didn't matter, since it would be the same. I don't know enough about electronics to know what the voltage difference would do -- I just know how to swap parts in and out..

Got home, put the fuse in, and fired it up. The gray thing under the glass fuses got red really fast (one or two seconds), and started smoking, and I turned it off as quickly as possible.

So I've got a few questions --

1. What is the gray thing, and what's it do?

2. Do I need a 12A 250V fuse (as opposed to the 12A 32V I did get), and did I read the 3AB type correctly on the Littelfuse that I pulled from the SX-1250? Would this have caused the gray thing to heat up?

3. Any suggestions on what to look for/do from here? I'll be ordering a service manual from the eBay seller provided in the other link, but it'll take a few days to get here. Until then, it's taking up a ton of room on my "bench" (e.g. kitchen table)...

Thanks for any help!

 

[tentoze]

vwap,

First off, welcome to AK.

Second, from one non-technical person to another- if you want that receiver to function properly, please take it to a qualified technician and get it repaired.

 

[Fernzee]

Hi, and welcome to AK. The fixes to your questions here are.

First, do you know a multimeter? Second, have you ever sodered? If the answer to both of these questions is no, then I strongly suggest you find a qualified audio repair person to do the actual work.

Again, welcome.

 

[Unican_Eric]

Hi and welcome to AK. Congrats on owning a 1250. Now I have to agree with the 2 above comments. You really have to take it to a qualified service tech. Good luck.

 

[EchoWars]

The guy who sold you the fuse is a moron. A 32V fuse will arc even when 'blown' if used in 120V/220V gear. There's a reason that fuses have voltage ratings.

You have serious problems. The fact that you are here asking questions about 'the gray thing' is my tip-off that you're in over your head. It is the soft-start resistor, and is never supposed to get hot unless the relay that jumpers across it will not close, as will happen if there are blown outputs or a problem with the regulator board.

Your 1250 needs professional help. If you need suggestions as to a repair facility, I'm sure you can get suggestions here. The 1250 is a classic piece, and you should choose your repair person carefully (I've seen too much horrid work done on beautiful receivers, so the goal is to find someone with a clue...)

 

[cincy]

vwap, welcome to AK. The clerk sold you the wrong fuse. 12amp 32volt is used in older automobile systems. He should have checked your ceramic fuse with a volt ohm meter because you have no visual as to its condition. The advice of our fellow AK'rs above should be taken seriously. A lot of our members own the SX 1250 and its value is growing so that it would be worth the expense of having it properly serviced by a reputable tech. Since you show an interest in electronics I would purchase a digital volt ohm meter, which can be bought for $10 dollars or less and have seven functions or so. I have bought some at Harbor Freight for as little as $2.99 on sale, nine volt battery included and have given them to my son and a friend as gifts, they're fine for general use. Getting the service manual is good idea as not every tech has a manual for all equipment that they work on and that could save them time and you money. Also, they can point out to you what they repaired or replaced so you will have a better idea of where to look in the future.

 

[vwap]

Thanks everyone.

Yes, I know what a multimeter is, and I did check my ceramic fuse, and it is indeed blown.

I was pretty certain a 32V fuse isn't what I was looking for, but the guy seemed positive there was no such thing as a 250V 12A; his exact words were: "They don't make a 3AB in anything besides a 32V, so no matter what your fuse says, I guarantee this is what you're looking for."

I do have the ability to solder. Like I said, I know how to replace things, but I may not know what they do. (In other words, given a schematic, I am able to figure out what each part, and if necessary (basic things like resistors being within their rating, leaky caps and such) and the part is available, buy a replacement and put it in). I haven't had huge exposure to electronics, and though I know some of the basics, I do understand that there's a plethora of knowledge I'm lacking, and for my ignorance, I apologize.

I started this 'repair' with the hope that it was a simple fix -- leaky caps, blown resistors, blown fuses. Evidently, as the soft-start resistor is the one heating up and it shouldn't be unless there's a larger problem at hand, it doesn't seem to be an easy fix.

Is there a way I can check to see if the outputs are blown, or if the regulator board has something that's not functioning properly?

My income right now isn't such that I can get it professionally looked at, which is why I'm hoping to, with some help, fix it myself and learn something in the process. If you still think this is something that's well beyond my (admittedly minimal) skills, then feel free to reaffirm your feeling, and I'll re-shelve the amp until I can have it looked at. (It's been shelved for over a year now.. )

Thanks again.

 

[fropiler]

The guy who sold you the fuse is a moron. A 32V fuse will arc even when 'blown' if used in 120V/220V gear. There's a reason that fuses have voltage ratings.

You have serious problems. The fact that you are here asking questions about 'the gray thing' is my tip-off that you're in over your head. It is the soft-start resistor, and is never supposed to get hot unless the relay that jumpers across it will not close, as will happen if there are blown outputs or a problem with the regulator board.

Your 1250 needs professional help. If you need suggestions as to a repair facility, I'm sure you can get suggestions here. The 1250 is a classic piece, and you should choose your repair person carefully (I've seen too much horrid work done on beautiful receivers, so the goal is to find someone with a clue...)

Heed the above advice. I have a strong background as a former electronics tech, and am probably in over my head taking on a project like this.

If you do feel that you must proceed, know when to quit. That would be before removing any board level components, as it does take a skilled hand with the soldering iron in order to avoid nasty damage to wires and traces on the circuit boards.

Good luck, and welcome!

 

[EchoWars]

I was pretty certain a 32V fuse isn't what I was looking for, but the guy seemed positive there was no such thing as a 250V 12A; his exact words were: "They don't make a 3AB in anything besides a 32V, so no matter what your fuse says, I guarantee this is what you're looking for."

Your friendly neighborhood Lowe's or Tru-Value Hardware will have the proper fuse. 12A, fast acting. FWIW, unless the fuse is labeled 'slo-blo' (nowadays, the slo-blo fuses are wound on an element in the center...you can't really confuse it with a regular fuse) it is considered quick acting.

I do have the ability to solder. Like I said, I know how to replace things, but I may not know what they do. (In other words, given a schematic, I am able to figure out what each part, and if necessary (basic things like resistors being within their rating, leaky caps and such) and the part is available, buy a replacement and put it in). I haven't had huge exposure to electronics, and though I know some of the basics, I do understand that there's a plethora of knowledge I'm lacking, and for my ignorance, I apologize.

I'll apologise too...in advance, for saying that you are what we say 'knows just enough to be dangerous'. In other words, turns a $75 repair into a $350 repair.

Is there a way I can check to see if the outputs are blown, or if the regulator board has something that's not functioning properly?

Pull the outputs out, and visit this thread. If you have lost a few outputs, then I can about guarantee that the driver board is smoked to some degree also, and will require a careful going-over. As far as the regulator goes, the service manual and the schematic gives all the necessary voltages and places to measure them.

My income right now isn't such that I can get it professionally looked at, which is why I'm hoping to, with some help, fix it myself and learn something in the process. If you still think this is something that's well beyond my (admittedly minimal) skills, then feel free to reaffirm your feeling, and I'll re-shelve the amp until I can have it looked at. (It's been shelved for over a year now.. )

Thanks again.

OK...I know I seem harsh here, but I've spent the last couple of years repairing gear that has been nearly made unusable by the previous tech, who always comes 'highly recommended', or well-meaning owners short of funds who know 'a little' and think that with enough determination that they can fix it. It, of course, is not enough to know what individual components do...as a group, they make up a system designed to perform a specific function. What is needed is a clear understanding of how that function is performed, and the role the individual components play in that grand scheme.

Why am I going off on this deal? Beats me... The SX-1250 is a fine piece, and there's just about nothing on it that can't be fixed pretty easily. But, it is NOT the piece to learn on. You want to learn a bit about repair, go buy a few beater amps on fleabay and tear into 'em. You have a nice classic receiver and need it fixed? Get it to someone who knows how, and save a lot of grief, for you and the tech.

Yeah, I'm a hard-ass. Better than than see another 1250 show up as a parts unit at Oaktree. My apologies to the faint of heart. :yes:

 

[kaiser_will]

The ceramic 12A 250V 3AB seemed blown. I went to the local electronics store, and they sold me a pack of Littelfuse 12A 32V 3AB fuses, mentioning that in the 3AB format, there's only one 12A, so regardless of what my fuse said (he wouldn't even look at the fuse I had), the voltage didn't matter, since it would be the same. I don't know enough about electronics to know what the voltage difference would do -- I just know how to swap parts in and out..

I also own an SX-1250 and also had major problems finding the right fuse. I was sent out the door with a box of 32V/12A fuses and had to go back and arm wrestle the clerk to open his Bussman catalog to find out that, dog gone it, they DO make 120V/12A ceramic fuses.

Anyway, if you you did not blow the replacement 32V fuse then replace it with the right voltage rating before proceeding. Next, if the 12A mainline 120VAC fuse DID blow, I do not believe that the "gray thing" should have been glowing. This fuse is the mainline protection that all AC line power comes through.

If the mainline 120VAC/12A fuse is blowing, the unit is suffering a short to ground somewhere. This could be many, many things (failed MOSFET output transistor, melted wire, power supply failure, etc.).

Lastly, save yourself the $15 for the service manual copy from Ebay. Shoot me an email at kaiser_will_1967@hotmail.com and I will snail-mail you a copy of my manual. It will photocopy just great and be good enough to get the job done. When you have it working top-notch, you can buy an original manual to help increase the value of the unit.

 

[agger]

... (failed MOSFET output transistor, melted wire, power supply failure, etc.).

there are no mosfet outputs in a SX-1250, the are bipolar!

But anyway, if they are blown you could end up in a problem like this.
I'm wondering about your saying that the unit worked intermittend. This means the outputs were OK at that time and the protection switches you off due to regulator problems, leaky caps, detuned offset or bias, or whatever...

So if you are not the electronics expert, I second the recomendation to give this 1250 to a good repair shop! its not a training object!

 

[Fred Longworth]

I agree with the excellent advice you've received so far.

* * * * *

The SX-1250 is a gem, but on a scale of 1-10 as far a how hard it is to repair, I would give it an 8 or 9. It uses sophisticated circuitry (for a unit more than 25 years old) and it is huge and bulky to work on.

If I (a service dealer) sold a 32v fuse in a 125/250v application, and the Bureau of Electronics and Appliance Repair (California) found that I did this, I would receive a citation. If it happened repeatedly, I could lose my servicer's license.

I am a member of Nesda (National Electronics Service Dealers Association). If you email me privately, I can recommend a member dealer in your area. For example, Dave Wreski, who owns Eastern Stereo/Videologic in New Jersey is as good as they come.

But . . . as a general paradigm for repair, if there is a "short," the first step is to identify the short. The second step is to disconnect or disable it, and, with this no longer in circuit, operate the machine (without loads) to see what else, if anything, is seriously wrong.

For example, if I get a stereo amp in that's blowing fuses, I identify the shorted parts (usually output transistors) and -- assuming I don't see a trail of burned resistors in the driver stages -- I then disconnect the shorted transistors. Next, I turn the set back on, usually with a smaller fuse. (I may go down from 8 amp to 4 amp.) In 85% of the cases, the set will run. I then put it through a performance check to define what else needs service attention.

But, in doing this, I use a digital multimeter, an oscilloscope, a signal generator, a bench espressly set up for repair, and 35 years experience with these machines.

I also -- often before I even go looking for the short -- give the set a thoroughgoing visual inspection. Has the set been dropped? Has it been worked on before? If so, by someone skilled or by an idiot? Are there visible signs of damage? Burned resistors? Cracked circuit boards? Residues from a fluid spill? Missing screws and loose boards?

* * * * *

Good luck with your machine.

Fred Longworth
StereoTech Classic Audio Repair
http://www.repairaudio.com

 

[crooner]

Fred, good to have you here in San Diego!

It's recomforting to know, because for years many thought the only qualified vintage tech in the area was that fella driving a beat-up 1970's Datsun pick-up.

It's nice to have some choices! :thmbsp:

 

[vintagestereo]

vwap,

First off, welcome to AK.

Second, from one non-technical person to another- if you want that receiver to function properly, please take it to a qualified technician and get it repaired.

Amen!

 

[vintagestereo]

I agree with the excellent advice you've received so far.

* * * * *

The SX-1250 is a gem, but on a scale of 1-10 as far a how hard it is to repair, I would give it an 8 or 9. It uses sophisticated circuitry (for a unit more than 25 years old) and it is huge and bulky to work on.

If I (a service dealer) sold a 32v fuse in a 125/250v application, and the Bureau of Electronics and Appliance Repair (California) found that I did this, I would receive a citation. If it happened repeatedly, I could lose my servicer's license.

I am a member of Nesda (National Electronics Service Dealers Association). If you email me privately, I can recommend a member dealer in your area. For example, Dave Wreski, who owns Eastern Stereo/Videologic in New Jersey is as good as they come.

But . . . as a general paradigm for repair, if there is a "short," the first step is to identify the short. The second step is to disconnect or disable it, and, with this no longer in circuit, operate the machine (without loads) to see what else, if anything, is seriously wrong.

For example, if I get a stereo amp in that's blowing fuses, I identify the shorted parts (usually output transistors) and -- assuming I don't see a trail of burned resistors in the driver stages -- I then disconnect the shorted transistors. Next, I turn the set back on, usually with a smaller fuse. (I may go down from 8 amp to 4 amp.) In 85% of the cases, the set will run. I then put it through a performance check to define what else needs service attention.

But, in doing this, I use a digital multimeter, an oscilloscope, a signal generator, a bench espressly set up for repair, and 35 years experience with these machines.

I also -- often before I even go looking for the short -- give the set a thoroughgoing visual inspection. Has the set been dropped? Has it been worked on before? If so, by someone skilled or by an idiot? Are there visible signs of damage? Burned resistors? Cracked circuit boards? Residues from a fluid spill? Missing screws and loose boards?

* * * * *

Good luck with your machine.

Fred Longworth
StereoTech Classic Audio Repair
http://www.repairaudio.com

Fred -- Great post. Thanks for the insights!

-- Chris