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just picked up an sx 1250....some issues..no sound, blowing fuses, etc

9

91rtstealth

Active Member
ok...so my mechanic has had this sx 1250 running the radio of his shop as long as I can remember..i've been drooling over it for years....a few months back I noticed he had a radio on top of it and some other crap piled on it...so I asked him if it worked anymore, and he said it didn't "click on anymore" and had no sound...well, today he finally said I could have it!!

I took it home, cleaned it up, and surprisingly it's pretty clean inside....now:

1. if you turn it on, you never hear the amp kick on...so there's no sound...
2. none of the indicator lights work (source lights and the speaker set lights do not come on....but the radio dial background lights up)

I took the case off and the bottom panel....I found that there is a section on the bottom where 4 1 amp fuses were.....the 2 fuses closest to the back of the receiver were blown...i ran to radio shack immediately excited by the thought of it working by just replacing the fuses..hah...well, as soon as I put the fuses in and turned it on, they blew...so there's a short somewhere...does anyone have any idea what it could be? what do those 2 fuses control? I imagine it's one of the big caps inside....what do you think?
 
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You likely have blown output transistors, among other things. The OT's are the shiny round things attached to the heat sinks.
 
Power supply issue (or it would blow a lot bigger fuse than a 1A). Probably a missing voltage on the regulator board. Check them all.
 
Not so fast... not the output transistor (yet)

Those 2 fuses (orange wires) are the +/-85v power going to the +/-65v regulated power supplies. The loss of the +65v also shuts down the 13v to the tuner and the 5.4v to the dead lamps. (the main dial illumination is 8v ac, and the 5th fuse on the board)

Rebuild the regulated power supply board (awr-106, removable) and recap / rediode the awr-107 "fuse" board (not removable).

There is another recent 1250 thread where the parts lists are published.

There will be an issue of perhaps something off those boards blowing them up, that could probably be the 2 capacitors on each amplifier card (left and right sides) which can be replaced preemptively (and a few others) the same time as the 106 and 107 boards are rebuilt. Those boards are ALSO removable.

When we're done, they'll be good for another 20 to 30 years, at a parts cost of about 20 bucks plus parts shipping - IF you do it yourself.

Are you game?
 
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markthefixer said:
Not so fast... not the output transistor (yet)

Those 2 fuses (orange wires) are the +/-85v power going to the +/-65v regulated power supplies. The loss of the +65v also shuts down the 13v to the tuner and the 5.4v to the dead lamps. (the main dial illumination is 8v ac, and the 5th fuse on the board)

Rebuild the regulated power supply board (awr-106, removable) and recap / rediode the awr-107 "fuse" board (not removable).

There is another recent 1250 thread where the parts lists are published.

There will be an issue of perhaps something off those boards blowing them up, that could probably be the 2 capacitors on each amplifier card (left and right sides) which can be replaced preemptively (and a few others) the same time as the 106 and 107 boards are rebuilt. Those boards are ALSO removable.

When we're done, they'll be good for another 20 to 30 years, at a parts cost of about 20 bucks plus parts shipping - IF you do it yourself.

Are you game?
Click to expand...

thanks for the info...it is the two fuses connected to the orange wires....and I don't think I have the patience or money to repair all of that..haha. I might just sell it as is. Is there any way I can test for sure to see what the problem is? that make sense, but how do I know if it's the regulated power supply board or the big monster capacitors themselves?
 
91rtstealth said:
thanks for the info...it is the two fuses connected to the orange wires....and I don't think I have the patience or money to repair all of that..haha. I might just sell it as is. Is there any way I can test for sure to see what the problem is? that make sense, but how do I know if it's the regulated power supply board or the big monster capacitors themselves?
Click to expand...

short explanation - cuz I said so :stupid: ?

longer explanation - the big fuse wasn't blowing - they are entirely separate.

The regulator board (and amp boards and protection board) can be removed, shipped, fixed, returned and reinstalled...
might get you back up and running. I do stuff like that...

or keep me in mind (line) if you want to just pass it along. Fixing 1250's is FUN :D ...
 
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markthefixer said:
short explanation - cuz I said so :stupid: ?

longer explanation - the big fuse wasn't blowing - they are entire separate.

The regulator board (and amp boards and protection board) can be removed, shipped, fixed, returned and reinstalled...
might get you back up and running. I do stuff like that...

or keep me in mind (line) if you want to just pass it along. Fixing 1250's is FUN :D ...
Click to expand...

hmm...i actually want to learn more about repairing this stuff cuz I love vintage audio..and since I want a collection, I my as well learn how to repair these old pieces...I think I might just pull these 2 boards and see if something is shorting...is it something I could likely see? I've repaired several engine and suspension computers from dodge stealths/mitsubishi 3000gts because you can SEE where the problems are on those..leaky capacitors...
 
You got a free 1250 --Wow!! Spend the $ and bring it back to life --- Believe me you won't be sorry.
As stated in a previous comment the boards are removeable -- and there are people on this website who will rebuild them for you if you are gun shy about doing things like that -- you might be within driving distance to one of our techs.
This receiver is one of Pioneers best and is worthy of a new life in your hands.
 
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JHS2RT said:
You got a free 1250 --Wow!! Spend the $ and bring it back to life --- Believe me you won't be sorry.
As stated in a previous comment the boards are removeable -- and there are people on this website who will rebuild them for you if you are gun shy about doing things like that -- or -- depending on where you live (and who knows since your city is not listed)-- you might be within driving distance to one of our techs.
This receiver is one of Pioneers best and is worthy of a new life in your hands.
Click to expand...

yeah I was pretty excited too...I would have given him some money, but he told me I could just take it...I was talking with him for about two hours about audio..i've been going to the guy for years and I had no idea he was into audio and other vintage stuff...he's more into the expensive mcintosh tube stuff so he probably didn't have a need for this receiver...but yeah, it was cool talking to him...

I was thinking of trying ot fix it, but I really would rather have an sx1280..i'm a sucker for vu meters..that or a sansui g9000...what do you guys think? g9000/9000 or sx1280/1080?

winter is approaching..it could be a nice winter project, but I have no patience whatsoever..and I had doing stuff like this without a lot of knowledge and guidance...I do want to learn more about fixing these old pieces though..could be a place to start...

I just updated my profile..palmerton, pa...I doubt I am close to any techs..that would be a great if I was...but i'm broke anyways..haha...I have a reel to reel guy close to me in pottstown, pa..other than that, i'm not aware of anyone else...
 
I figure you can do that power supply (106 board) and the 4 high voltage caps on the amp for between 20 to 30 dollars parts shipped....

looks like $16.37 for the 106 board, excluding some heat sink compound

and a wait until Dec 1 for the amp & 107 board caps (470uf 100v), IF needed.

we've already got two 106 board repair threads in action, three's no problem.
I can talk you through, down to a really basic level to get you started.
BUT
swapping caps already has you soldering/desoldering and recognizing polarity
so transistors aren't much harder...

piece of cake....

check out some of my old repair threads.....
you'll see I have plenty of patience, and we'll take it in easy steps.
the most onerous part will be polishing up the pins on the board that the connectors mate to.
 
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markthefixer said:
I figure you can do that power supply (106 board) and the 4 high voltage caps on the amp for between 20 to 30 dollars parts shipped....

looks like $16.37 for the 106 board, excluding some heat sink compound

and a wait until Dec 1 for the amp & 107 board caps (470uf 100v), IF needed.

we've already got two 106 board repair threads in action, three's no problem.
I can talk you through, down to a really basic level to get you started.
BUT
swapping caps already has you soldering/desoldering and recognizing polarity
so transistors aren't much harder...

piece of cake....

check out some of my old repair threads.....
you'll see I have plenty of patience, and we'll take it in easy steps.
the most onerous part will be polishing up the pins on the board that the connectors mate to.
Click to expand...

cool...well, I think I might just fix it to sell it..so I want to just fix what's needed to get it going and get rid of it..however, I always say that, and then I fall in love with it and keep it..haha..but i'd rather have a 1280 or g9000...so yeah, i'm a "if I ain't broke, don't fix it" kind of guy..haha....so where should I start as of now? take out the 106 board and inspect? if so..where is it and how do I remove it? haha..
 
Download the service manual, it will explain locations etc, two screws hold the board to a steel plate.

No disassembly for now, the parts list in the other thread is directly applicable but you can substitute 526-NTE303 5 x 1gram tubes $2.77 for 532-249 1 oz thermal compound $4.71


http://www.audiokarma.org/forums/showpost.php?p=4115434&postcount=89


has a Bill Of Materials text block that can save you a LOT of typing of alphabet soup.
at Mouser.com
establish a logon identity, to access EZBuy
go to EZBuy (top line of tabs in the page)
Use BOM entry with that text block (copy from here, then paste to there) starting with the line AFTER "bom import:"
 
thanks a lot for the info..i brought the BOM...i think this is way beyond my know-how..haha..i don't even know what half of that stuff is...i think if I try to fix it i'll completely screw it up...

it would be easier for me to send that part out for repair instead of rebuild...i must remind you that I am extremely broke at the moment..haha..I just want to pull the board and see if I can see a short or anything like that..or is that not even worth it?
 
You would need to look on the bottom of the 107 board for any shorts, BUT it is most likely that the parts on the 106 board just cooked to death over the years.

You don't need to know the parts, half are caps, about half are transistors, a few diodes and two adjustable resistors. I'll talk you through it, part by part at first until you gain confidence - we'll start with the caps, then the diodes, the adjustable resistors and finally the transistors. Quickest, cheapest way.

along the way the board will look less and less complex, and as you learn how to spot parts from the parts list to the physical location on the board it will all make sense. The parts will come in individually marked bags, but with repeats if there are two or more of the same value.

for example: c19, it's on the parts list, and also on the board layout diagram. you will have the new one in your hands and see it's 47uF or 47 microfarads at 10v or 10 volts. There will be a similarly marked one on the board, pull out the old, put in the new - watching to be sure the polarities are correct.
do that 16 times one at a time and you are HALFWAY DONE!!


Right now I am swamped with stuff, maybe somebody else would do the board rebuild (sooner?).
 
markthefixer said:
You would need to look on the bottom of the 107 board for any shorts, BUT it is most likely that the parts on the 106 board just cooked to death over the years.

You don't need to know the parts, half are caps, about half are transistors, a few diodes and two adjustable resistors. I'll talk you through it, part by part at first until you gain confidence - we'll start with the caps, then the diodes, the adjustable resistors and finally the transistors. Quickest, cheapest way.

along the way the board will look less and less complex, and as you learn how to spot parts from the parts list to the physical location on the board it will all make sense. The parts will come in individually marked bags, but with repeats if there are two or more of the same value.

for example: c19, it's on the parts list, and also on the board layout diagram. you will have the new one in your hands and see it's 47uF or 47 microfarads at 10v or 10 volts. There will be a similarly marked one on the board, pull out the old, put in the new - watching to be sure the polarities are correct.
do that 16 times one at a time and you are HALFWAY DONE!!


Right now I am swamped with stuff, maybe somebody else would do the board rebuild (sooner?).
Click to expand...


there's no hurry..haha...i'm very broke at the moment....and finding a new job or some source of income in crucial..hah..

i'll think about it...i'm just afraid i'll end up messing it up more than it already is...i have absolutely no patience and a bad temper...I remember I had a heck of a time fixing my engine computers...but I did get better at soldering...i just suck at de-soldering..haha..
 
ok..so i'm currently at the work bench at home..i just removed the 106 board and the big 25v 1000uf cap is leaking quite badly...as well as the two caps in the middle with 77b printed on them...

and it smelled like something burning in this area of the receiver...

in addition, the 107 board also has 2 caps leaking quit badly..they have 77R printed on them...they are 25v 470uf...
 
91rtstealth said:
<snip?
I took the case off and the bottom panel....I found that there is a section on the bottom where 4 1 amp fuses were.....the 2 fuses closest to the back of the receiver were blown..<snip> as soon as I put the fuses in and turned it on, they blew..<snip>
Click to expand...

Those would be f1 & F2, the +/-85v on the orange wires from the transformer, and using 470uf 100v capacitors .

91rtstealth said:
ok..so i'm currently at the work bench at home..i just removed the 106 board and the big 25v 1000uf cap is leaking quite badly...as well as the two caps in the middle with 77b printed on them...

and it smelled like something burning in this area of the receiver...

in addition, the 107 board also has 2 caps leaking quit badly..they have 77R printed on them...they are 25v 470uf...
Click to expand...

While this is F3 & F4 (green wires), the ones closest to the fifth fuse on the opposite end of the board.They feed the 470uf 25v and 1000uf 25v caps.

What condition were they in.

The fact that f1 and f2 blew is completely separate from the 470uf 25v, and 1000uf 25v caps ALL leaking on the F3 & F4 (green wires) circuit - THAT sounds like D5 or D6 is shorted, allowing AC current into those capacitors, which causes them to heat up, leak and possibly explode although the fuses are supposed to blow a LOT sooner. Be sure they are really 1 amp fuses.

So now it becomes necessary to rebuild the 107 board, which means replacing the 4 caps I mentioned in the other thread and six 1n4004 diodes to replace d1 through D6.

4 caps needed for the 107 ( awr-107 awr107 )
2x 470 uf 100v ceb (axial) 647-TVX2A471MCD $3.18 ea
2x 470uf 25v cea (radial) 647-UPW1E471MPD $0.47 ea

just an FYI, for more general reference, you can get 6 diodes too:
6x 512-1n4004 for a complete electrical power supply rebuild.
Click to expand...
about another 9 bucks in parts...
 
markthefixer said:
Those would be f1 & F2, the +/-85v on the orange wires from the transformer, and using 470uf 100v capacitors .



While this is F3 & F4 (green wires), the ones closest to the fifth fuse on the opposite end of the board.They feed the 470uf 25v and 1000uf 25v caps.

What condition were they in.

The fact that f1 and f2 blew is completely separate from the 470uf 25v, and 1000uf 25v caps ALL leaking on the F3 & F4 (green wires) circuit - THAT sounds like D5 or D6 is shorted, allowing AC current into those capacitors, which causes them to heat up, leak and possibly explode although the fuses are supposed to blow a LOT sooner. Be sure they are really 1 amp fuses.

So now it becomes necessary to rebuild the 107 board, which means replacing the 4 caps I mentioned in the other thread and six 1n4004 diodes to replace d1 through D6.


about another 9 bucks in parts...
Click to expand...

just a warning..i ask a lot of questions..it's how I learn..haha...so here we go:

are the 470uf 100v caps the two with 77b printed on the tops of them? those are the ones that use fuse 1 and 2 with the orange wires?

so answer your question, the 470uf 25v and 1000uf 25v caps were leaking quite badly...ALL the caps I mentioned were leaking a fair amount..unfortuntely, I don't have a digital camera because my gf left it at a baseball game..haha...

what do you mean by the d5 and d6 shorted?

they are definitely 1 amp fuses..i made sure

and how do I rebuild the 107 board if it's not removable? I thought you said it wasn't?


also..my biggest question is this:
with my engine computers i've repaired in the past, i was told that the caps would still function if they were leaking, however, the fact that the fluild was leaking meant that it could actually damage the board and short circuits...so my question is...if I clean up the leaking fluid on the board and make sure it's not interumpting other circuits, couldn't I pop 2 fuses in just to see if they blow or not..if they don't blow, and the receiver kicks on, I coult then be sure that replacing all of this stuff would remedy my problems...what do you think?
 
Right now you have TWO, SEPARATE, FATAL problems in the receiver's power supply. Not leaking crud shorting things out.

Either problem is capable of causing irreversible damage elsewhere in the receiver all on it's own when powered up.

NEITHER problem is a quick fix - or I would have guided you to it.

diodes let current flow one way only - establishing a polarity, shorted diodes let current flow both ways - which kills electrolytic caps because reversing their polarity turns the cap into a short circuit - heating it up instantly.

The 107 board has enough slack on the wires to get at the bottom, the 4 other boards come completely out - most of the work on receivers is done using slack in the wiring to get at the boards for work. Having removable boards is both a luxury and a pita because of the connectors and having to clean them.

The 100v caps WILL HAVE 100 on them instead or 25.

The engine computer caps you speak of could have shorted out and brought everything down, even going as far as popping like a firecracker.

SO can these leaking caps, and the "leakers" were leaking rather than exploding. There is serious damage internally in them, and with ALL THREE on the same circuit showing damage at the same time, it means they are a symptom, not a cause. Shorted diodes d5 and or d6 are the most likely cause, and the capacitor damage will not go away or get better, or even limp along after the diodes are fixed. Chances are they have burned their foil plates together internally - vaporizing the foil connections as the damage creeps along the capacitors toilet paper roll type structure like a cigarette burning as the power is reapplied.
 
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