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troubleshoot Pioneer SX-2900
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scar



Joined: 02 Jul 2015
Posts: 34

PostPosted: Thu Jul 02, 2015 2:45 am    Post subject: troubleshoot Pioneer SX-2900 Reply with quote

so my dad had a brain fart and left a drink that was condensing on top of our Pioneer SX-2900 receiver. some water dripped into it and now it doesn't function. the power button makes it click on/off, but there is no sound and no display. i'm trying to see if there's anything i can do to repair it. upon inspection, i don't really see any rust or burned areas in the circuitry.

however, i noticed that one of the fuses was blown. it's fuse #53 in the service manual[1], a 4A/125V fuse. so i thought i'd try replacing that first. i read that i can use fuses rated with a higher voltage as long as the amperage is the same, so i picked up some 4A/250V fuses at RadioShack.

unfortunately, as soon as i powered on the receiver the fuse blew out again. the fuses i got were "fast acting" though, and have a thin wire; there were some other 4A/250V "slow blow" fuses available too which had a thicker wire... i'm wondering if i should try one of those? the official Pioneer part number is AEK-100[2], discontinued and replaced by GEK-007; maybe i need that fuse specifically? or is the fact that a "fast acting" fuse blew out immediately indicative of another problem elsewhere?

1. http://www.hifiengine.com/manual_library/pioneer/sx-2900.shtml
2. http://parts.pioneerelectronics.com/part.asp?productNum=AEK-100
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jts1957



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PostPosted: Thu Jul 02, 2015 4:15 am    Post subject: Reply with quote

1) I thought Radio Shack went the way of the Pony Express, telegraph, Edsel, etc.
2) There are two basic types of fuses available for appliances and consumer electronics: fast-acting or time-delay. Any replacement fuse must match the one it’s replacing. In general, fast-acting fuses are a single strand of wire or strip of metal. Time-delay fuses usually have a coiled wire, a thick element wrapped in wire, or a spring.
3) There is likely a problem elsewhere.

I'd start by measuring each power supply source to ground to see if one is shorted
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scar



Joined: 02 Jul 2015
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PostPosted: Thu Jul 02, 2015 5:41 pm    Post subject: Reply with quote

thanks jts1957... umm can you be more specific? do you mean measure the transformer while the unit is plugged into mains? sorry i just have a basic understanding of electronics and a cheap volt meter from harbor freight Very Happy
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jts1957



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PostPosted: Thu Jul 02, 2015 6:45 pm    Post subject: Reply with quote

I'm presuming the 6800ufd capacitors involved are discharged and that your meter is a auto-ranging digital-type and that you have read its operating instructions.

Since the relay clicks when you try to power ON, Standby power is working.
Since the fuse remains intact until you try to power unit ON, there is a problem with T1 (unlikely) or on something connected to its secondary winding(s).

With your meter on OHMS, measure ACROSS each of the following:
C701
C702
C704
C706
Report any LOW resistance readings
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jts1957



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PostPosted: Thu Jul 02, 2015 6:47 pm    Post subject: Reply with quote

Unit UNPLUGGED from Mains.
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scar



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PostPosted: Thu Jul 02, 2015 8:20 pm    Post subject: Reply with quote

thanks jts. actually i think i misspoke. the fuse actually blows out as soon as i plug in the unit to mains. maybe it wouldn't if i put in a time-delay fuse instead?

and i'm not sure i'm equipped to measure across those first two big capacitors (C701, C702). they are so large, even C704 is too big. i don't see a way to access the contact points without removing the whole circuit board so i can get underneath it.... is that what i'm supposed to do? there's a ton of screws and plastic pins to remove....

i could measure C706 though and it topped off around 12.5 kohms
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jts1957



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PostPosted: Thu Jul 02, 2015 8:59 pm    Post subject: Reply with quote

Unless relay contacts are 'welded' together or relay energizes just for an instant - 'was last ON' memory), Mains can't get to FU1 (#53).

You DO have the SM. You may measure between the metal chassis and ANY point that the positive pin of each capacitor connects to.
The '+' of D701 for C701.
The '-' of D701 for C702 (note polarity reversed - won't matter when checking for a short).
The last pin of J2 (furthest away from largest caps)

You are aware that at some point you will likely need to access the bottom of the board to desolder a bad component, replace it and resolder?
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scar



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PostPosted: Thu Jul 02, 2015 10:04 pm    Post subject: Reply with quote

what square is D701 in, in the complex assembly diagram?


yes i have a soldering iron and know how to use it... they actually have some components soldered to the chassis so i will need to desolder those to even remove the circuit board Razz
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jts1957



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PostPosted: Thu Jul 02, 2015 10:36 pm    Post subject: Reply with quote

C5. Next to C702.

When the time comes ...
Most open like a book, provided you can create enough slack. Mark screws/holes so that the right one goes back where it came from. Take back off ("38"), remove screw from regulator, remove 2 screws from heatsink (41), release all clips (24/25). Unplug connector(s), cut wire ties if necessary, unsolder #52, etc. Carefully try to swing open. Just keep transformer at the bottom and don't rest PCB edge with substantial weight on it.
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scar



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PostPosted: Thu Jul 02, 2015 10:45 pm    Post subject: Reply with quote

ugh lol i don't see it... i see D702, D703, D713... R701
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