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Pioneer SX-1250

the pre-amp section is working on my yamaha mx-800 power amp with both channels, hooked it up as a power amp and both sides played for a min. or so and then the right side quit, but left is still playing and hasn't popped or crackled any at all.

the tone controls and everything are working as a pre-amp. do you think the power amp boards need re-done?
 
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i don't think the relay on awm-091 is working right it hardly clicks. the one on the chassis near the caps works good and clicks loud
 
xXColdShotXx said:
i don't think the relay on awm-091 is working right it hardly clicks. the one on the chassis near the caps works good and clicks loud
Click to expand...

NOT the relay's fault, most likely it's Q5 (2sc1166) on the protection board, the relay driver transistor. OR Q6 (2sc1166) the voltage regulator transistor that makes the voltage to run the relay. Either could be getting tired.

I'm not sure if I have listed protection parts recently for the 1250.

protection circuits...
one: Q4, 512-KSD1616YTA to-92 ecb 60v 1a 0.75w 160mhz 135-400hfe $0.12 current dump transistor
relay driver transistor and voltage regulator
two: Q5, Q6 (2sc1166 50v, .2a .6w) 512-KSC2690AYSTSTU to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.80
one: C4 100uf/16v (100/35) 647-UPW1V101MPD $0.26 protection circuit timing capacitor
one: C3 4.7uf/25v (4.7/50) 647-UPW1H4R7MDD $0.14 protection circuit ac power on signal integrator
two: C5,C6 100uf/50v (100/50) 647-UPW1H101MPD $0.28 protection circuit voltage regualtor
two: C1,C2 470uf/6v (470/16) 647-UPW1C471MPD6 $0.34 protection audio input caps
 
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should i order enough parts to re-build both awh-048 boards also? i want it to sound as best as it can.

wonder why the right channel is still not working? flat amp board, control amp board or is it to do with the awh-048 power amp boards? or none of the above?
 
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the fact that one channel stays playing indicates there is no fatal fault occurring in either channel. Most bad things in amplifiers usually trip the protection. thus I don't think right now that you need to order amplifier parts.

DID YOU ORDER EXTRA TRANSISTORS, just about anything will do better temporarily than what's in the protection circuit regulator and driver transistors - they ARE itty-bitty transistors already. something labeled ksc- or ksd-...

the sound loss could be anything from a bad rca jack connection at the amp-in jack, through to the feeble y activated protection relay not actually pulling in both sets of contacts.

If i read that correctly earlier, the channel worked then got quiet, and you were running in source material from another preamp that WAS working, putting the blame on the power amp.

you did get nice dc offset voltages and idle current readings before.

as to why there was sound and then none while blaming the relay is because maybe the contacts are not exactly parallel and more force is needed to close all the contacts.

when the sound is out, perhaps you would want to temporarily adjust the dc offset at that channel to say 0.015V or 15 millivolts, then if the offset disappears at the speaker terminals you will know the amp output signal is just not making it through, even when there is no sound. if the 15 millivolts is there even though the sound is supposed to be going in, we will know the input signal is just not getting to the amp.

when there is no sound, check for the idle current's 100 millivolts between pins 7 and 19 of the "9.3 procedure".
 
no, i didn't order any extra transistors, but next time i will. i am gonna do dc-offset test and clean the pre-amp/power in connectors with deoxit and see if that helps. i will report back when done.

i tested dc-offset and got 0 mv on right channel (it didn't even fluctuate) and between .1 mv on left channel (did fluctuate at first, but not when warmed up), let sit for 20 minutes to warm up and tested again and i am getting 0 mv on both channels now, and the relay for sound is not clicking at all anymore.
i am getting .4 mv from pin 9 (+) and chassis ground on left side and -1.4 mv from pin 9 (+) and chassis ground right side.
i am getting 95 mv from pin 7 (+) to pin 19 (-) on both sides.

i am going to take AWM-091 out of the receiver for closer inspection, may find something wrong.
 
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The whole idea is why is the sound going away, and again, the numbers for the amplifiers are excellent - NO changes there.

How constant is the sound now? and after warm up?
 
no sound from either channel. i took out awm-091 board, the relay has a burnt spot on the inside, 2nd contact from right to left looking at non-foil side. it is to the right channel, not sure why left channel is acting up other than it being dirty.

here's the best pic i could take with this camera. i also noticed some oxidation on the 2 closest contacts (left channel). any way i can take that relay apart?


DSCF0955.jpg
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DSCF0995-0.jpg


i took the relay out (got a de-solder pump today) and the contact on the right side of the relay 2nd from the right is welded to its post that doesn't get any electrical current to, doesn't make much sense to be welded to that post, but it is. the 1st contact isn't welded, but there's not as much room between it and the ones on the left side of the relay because it's got a point to it on the back side and the others don't.
 
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i cut the welded contact, cleaned the good contacts and put it back on the board and in the receiver just to see if that helped any, and both channels are working good at same sound level. the relay clicks a lot louder now. do you have a part # for a new one, mark. thanks so much to everyone for the help you've given with this project. i still plan to re-do the rest of the boards in a few months.
 
how hard is it to take the volume out and apart to clean it? seems like the deoxit just isn't getting to it good enough. i got static from minimum to 2nd or 3rd notch. been listening to it for 2 days and just heard a scratchy sound coming from the left speaker at a real low volume, but no popping yet.
 
The unit must be desoldered to get cleaner into it. Until your soldering/desoldering skills improve, I'd leave it be. This is a hard one for even pro's to take out without tearing up the foil traces, since Pioneer bent the fat potentiometer leads down over the pads.
 
do you like restoring the pioneer spec 2, echo or markthefixer? if you do and you don't mind pm me some prices for what it would cost to restore a spec 1 and 2 at the same time, if you have time and want to fool with it. thanks
 
i checked the left channel only and it's kinda quiet scratchy sound and sounds like the volume is turned all the way up. not sure how to describe it, but it doesn't pop like before i re-built AWR-106 board. anyone have any idea what could be wrong with left channel? do i need to re-build AWM-091 and both AWH-048 boards now?
 
xXColdShotXx said:
i checked the left channel only and it's kinda quiet scratchy sound and sounds like the volume is turned all the way up. not sure how to describe it, but it doesn't pop like before i re-built AWR-106 board. anyone have any idea what could be wrong with left channel? do i need to re-build AWM-091 and both AWH-048 boards now?
Click to expand...
I don't know what you are trying to say...take another shot. :dunno:

As far as tackling other projects, that would have to be discussed via PM or email.
 
the left channel sounds like the volume is turned all the way up and it has a little scratchy sound sometimes, but the volume is at minimum, right channel doesn't do that.
 
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i am using it as a pre-amp at the moment and it isn't doing it through my yamaha power amp. just does it through it's own amp, maybe there's some bad caps and transistors on the left power amp. board? the volume is kinda dirty at low volume too.


i really don't mean to be annoying to anyone on here with the problems i am having with my stereo.
 
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Listen to your amp with the pre-out / amp in jumpers pulled. IF it isn't quiet, then your amps have problem(s) which is not unexpected.

Where was I? I've been BUSY.... :thmbsp:

Thing is that the amps also depend upon the output transistors, and you WILL have to test them and the resistors on the amplifier cards while working of the amplifiers.
 
the pre-amp works like a charm by itself, only acts up when the jumpers are in and only on the left channel. i have it's jumpers out and am using the pre-amp section of it with my yamaha power amp and it rocks. i can't wait to get it to where i don't have to worry about it tearing up at any time. is there any way you could post a bom re-build list of AWH-048, mark? i think i'd be better off to replace every transistor on AWM-091 instead of just 3.

are there any way to drill a real small hole in the volume pot to get deoxit in better instead of taking it off the board?
 
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