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SX-727 has a sad left channel

M

moped

New Member
I picked up an SX-727 and a pair of Ohm E2 speakers from CL on Sunday, and I have to say, I'm pretty pleased by the sound quality. I found AK while doing some research on what constitutes a fair price for the receiver, and subsequently what to do about the speaker plugs.

Mine came without plugs. The seller had wired up the speakers by shoving the stripped ends of the speaker wire into the sockets, but I wanted to do something a little more durable. I don't think I've seen what I did suggested here yet, so I'll mention that before I get into the description of my problem.

I went to the local hardware store and picked up a pair of cheap plugs like you would put on a lamp cord if for some reason the cord didn't have a plug already. I tore 'em apart, took out the prongs, snapped off some extraneous metal bits, flattened them and checked the fit.

With the receiver in the normal orientation, a normal width (i.e. not the fat one on a polarized plug) US plug prong will fit into the vertically oriented socket. The horizontally oriented one is a little smaller in the long dimension. Solution: file.

I soldered the prongs onto my speaker wire, added some heat shrink tubing to protect from shorts, and have been good to go since. They feel a little tight, but I read a thread somewhere here that .060" is the correct thickness, and the plug prongs seem close.

On to the meat and potatoes of the post:

The left channel has some crackling going on. It's normally pretty faint, but once in a while, the sound will cut out (the protection relay opening?). I guess I ought to do something about it.

Here's the information I have about the crackling:
1) It's source independent; FM, Phono, tape, AUX all crackle.

2) It's volume independent; with no source playing, the crackling remains at constant volume regardless of the volume setting.

3) It's speaker channel independent; I get it whether I plug into A, B, or C.

4) It's not the speaker; I've plugged the "right" speaker into the left channel, and I get crackling. Likewise, plugging the "left" speaker into the right channel causes no crackling.

5) Following the suggestion here (http://audiokarma.org/forums/showpost.php?p=4806340&postcount=17) I pulled the jumpers out of the back and the crackling went away. Sadly, I lack a known good amp to plug the preamp output into.

Right.

Two different threads:

http://audiokarma.org/forums/showthread.php?t=380007
http://audiokarma.org/forums/showthread.php?t=372548

Both suggest that this might be a failing transistor, possibly in the AF unit. There are 6 semiconductors in there according to the service manual (2 FETs 4 transistors) but I wouldn't have the faintest idea how to go about matching a modern replacement to fit the requirements of this application.

Actually, let me back up a step: I don't know the first thing about transistors, like for example what they're measured in. I know enough about capacitors and resistors that I can at least name the units they're specc'ed in (Farads/Volts, Ohms/Watts), and could probably dust of a physics textbook and explain an RC circuit if I had to. Unfortunately, that's as far as my analog knowledge goes.

I'm a programmer, so I don't actually deal with transistors as analog components on the (very rare) occasions that I deal with them at all (i.e. not since college when I did some stuff with 74 series TTL chips for a class). I can, however, solder, use a DMM, and know (roughly) what a scope does, if not how to actually set one up.

At this point, the questions I have are:

1) Have I followed the logic in the other threads correctly, and am therefore likely looking at a transistor issue in the AF unit?

2) If so, how would I go about finding a compatible replacement part?

3) Is there any point in trying Deoxit to solve this problem? I get that it's a generally good idea, but $30 is a lot to just throw at the problem; I'm actually a grad student of sorts right now.

4) Will it hurt the receiver or speakers to use them until I get some transistor info, put in a parts order, and replace the transistors? The crackling is pretty tolerable most of the time, turning up the volume to a pretty quiet level mostly drowns it out.

5) Besides a recap (and Deoxit if I'm feeling flush), is there anything else I should do while I have the hood open and the soldering iron out?

Anyhow, I just discovered AK on Friday, and I've got to say, wow. There are a lot of really knowledgeable and helpful people around here. Given some time, I hope to become one.
 
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1 yes, but may just be cleaning needed.
2 ask me(us)
3 deoxit works relative miracles.... it is labor intensive tho...
4 soft crackling, no loud yes
5 recap should run 20 bucks max.. probably lots less. (edit: DIY parts cost in 2011)

Deoxit first, that could cure it, because the usual problematic transistors are NOT in this unit. That isn't to say yours aren't, just that they are not the usual suspects.

The signal goes through every switch and pot in the unit, so it is worthwhile.

You COULD preemptively replace a few transistors,

512-KSA992FBU pnp (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea
512-KSC1845EBU npn (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea
from mouser.com are good subs for the head (phono) amp and control (tone) amp's transistors. 2sa 2sb are pnp transistors, 2sc, 2sd are npn transistors.

Thus the phono gets 6 ksc1845, and the control amp gets 2 ksa992 and 2 ksc1845 transistors.

This is a just thumbnail of the task, not tossing you in the deep end - and your research has served you quite well. That is an impressive first post. :D

but - we ALWAYS clean first - (and here's the rub - sometimes to clean one has to dig as deep as when replacing parts :dunno: )


edit - not bad..... (skip the tuner - you don't need that grief )

General c1 6800uF 50v CEW 647-UVZ1J682MRD 6800 63 $3.72
General c2 6800uF 50v CEW 647-UVZ1J682MRD 6800 63 $3.72
General c3 1000uF 63v CEW 647-UPW2A102MHD 1000 100 $2.06
General c6 220uF 10v CEA 647-UPW1A221MED 220 10 $0.18
General c7 330uF 16v CEA 647-UPW1E331MPD6 330 25 $0.28
General ? 220uF 50v CEA 647-UPW1J221MPD6 220 63 $0.62

phono /head amp
W21-002 c1 22uF 16v CEA 647-UPW1V220MDD 22 35 $0.15
W21-002 c2 22uF 16v CEA 647-UPW1V220MDD 22 35 $0.15
W21-002 c3 4.7uF 25v CEA 647-UPW1H4R7MDD 4.7 50 $0.12
W21-002 c4 4.7uF 25v CEA 647-UPW1H4R7MDD 4.7 50 $0.12
W21-002 c5 10uF 25v CEA 647-UPW1H100MDD 10 50 $0.12
W21-002 c6 10uF 25v CEA 647-UPW1H100MDD 10 50 $0.12
W21-002 c15 220uF 35v CEA 647-UPW1V221MPD 220 35 $0.22

tuner
AWE-015 c2 .47uF 50v CEA 598-DSF050J474 0.47 50 $0.29
AWE-015 c23 4.7uF 25v CEA 647-UPW1H4R7MDD 4.7 50 $0.12
AWE-015 c27 1uF 50v CEA 647-UPW1H010MDD 1 50 $0.12
AWE-015 c29 4.7uF 25v CEA 647-UPW1H4R7MDD 4.7 50 $0.12
AWE-015 c30 1uF 50v CEA 647-UPW1H010MDD 1 50 $0.12
AWE-015 c33 100uF 16v CEA 647-UPW1V101MPD 100 35 $0.26
AWE-015 c36 10uF 16v CEA 647-UPW1H100MDD 10 50 $0.12
AWE-015 c38 .47uF 50v CEA 598-DSF050J474 0.47 50 $0.29
AWE-015 c45 10uF 16v CEA 647-UPW1H100MDD 10 50 $0.12
AWE-015 c53 .47uF 25v CSSA 598-DSF050J474 0.47 50 $0.29
AWE-015 c54 4.7uF 25v CEA 647-UPW1H4R7MDD 4.7 50 $0.12
AWE-015 c55 3.3uF 16v CSSA 647-UKL1H3R3KDDANA 3.3 50 $0.20
AWE-015 c57 3.3uF 16v CSSA 647-UKL1H3R3KDDANA 3.3 50 $0.20
AWE-015 c58 1uF 50v CEA 647-UPW1H010MDD 1 50 $0.12
AWE-015 c61 .47uF 50v CEA 598-DSF050J474 0.47 50 $0.29
AWE-015 c65 100uF 16v CEA 647-UPW1V101MPD 100 35 $0.26
AWE-015 c66 2.2uF 16v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWE-015 c67 2.2uF 16v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWE-015 c73 47uF 16v CEA 647-UPW1E470MDD 47 25 $0.19

af amp
AWK-010 c7 47uF 50v CEA 647-UPW1H470MED 47 50 $0.22
AWK-010 c8 47uF 50v CEA 647-UPW1H470MED 47 50 $0.22
AWK-010 c13 2.2uF 25v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWK-010 c14 2.2uF 25v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWK-010 c15 47uF 10v CEA 647-UPW1E470MDD 47 25 $0.19
AWK-010 c16 47uF 10v CEA 647-UPW1E470MDD 47 25 $0.19
AWK-010 c21 2.2uF 25v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWK-010 c22 2.2uF 25v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWK-010 c27 2.2uF 25v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWK-010 c28 2.2uF 25v CSSA 647-UKL1H2R2MDDANA 2.2 50 $0.20
AWK-010 c29 100uF 6.3v CEA 647-UPW1A101MDD 100 10 $0.14
AWK-010 c30 100uF 6.3v CEA 647-UPW1A101MDD 100 10 $0.14
AWK-010 c31 47uF 50v CEA 647-UPW1H470MED 47 50 $0.22
AWK-010 c32 47uF 50v CEA 647-UPW1H470MED 47 50 $0.22

power amp
AWH-011 c7 22uF 10v CEA 647-UPW1V220MDD 22 35 $0.15
AWH-011 c8 22uF 10v CEA 647-UPW1V220MDD 22 35 $0.15
AWH-011 c9 220uF 10v CEA 647-UPW1A221MED 220 10 $0.18
AWH-011 c10 220uF 10v CEA 647-UPW1A221MED 220 10 $0.18
AWH-011 c15 100uF 50v CEA 647-UPW1H101MPD 100 50 $0.22
AWH-011 c16 100uF 50v CEA 647-UPW1H101MPD 100 50 $0.22

protection
AWM-027 c3 470uf 6.3v CEA 647-UPW1C471MPD 470 16 $0.34
AWM-027 c4 470uf 6.3v CEA 647-UPW1C471MPD 470 16 $0.34
AWM-027 c5 100uF 16v CEA 647-UPW1V101MPD 100 35 $0.26
AWM-027 c6 4.7uF 50v CEA 647-UPW1H4R7MDD 4.7 50 $0.12

power supply
AWR-011 c6 100uF 50v CEA 647-UPW1H101MPD 100 50 $0.22
AWR-011 c7 100uF 50v CEA 647-UPW1H101MPD 100 50 $0.22
AWR-011 c9 220uF 35v CEA 647-UPW1V221MPD 220 35 $0.22
AWR-011 c10 220uF 16v CEA 647-UPW1V221MPD 220 35 $0.22
AWR-011 c11 220uF 16v CEA 647-UPW1V221MPD 220 35 $0.22



current prices and availability have NOT been checked.
$21.21
 
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As much as it pains me to drop $40 on a couple of spray cans, I guess I'll try the Deoxit first. Just to summarize "The Idiot's Guide to Deoxit" and the ensuing thread before I go shopping:

1) Clean everything with Deoxit (D5)
2) Pots get FaderLube (F5)
3) Switches and contacts get Gold (G5)

A bunch of statements follow, and summarize what I think I've understood thusfar from your post, the service manual, and various other threads.

1) The AF unit is the preamp/tone amp.

2) The head amp precedes the AF unit in the amplifier chain

3) The phono signals run directly into the head amp

4) The tuner runs into the head amp through the CR unit (What is the CR unit?)

5) I'm getting crackling on all inputs, including ones that don't run through the head amp (tape, aux), so if there's a bad transistor, it's likely in the AF unit.

6) The 2SC458 are the "usual problematic transistors", the SM says the head amp has either those or 2SC781LG transistors. Regardless, the head amp probably isn't the problem because of point 5 so I shouldn't worry about it for now.

7) For the extra buck or so it'll cost me to buy transistors, I should just order them so I have them on hand.

8) Electrolytic capacitors (and some others) have polarity. Don't screw it up.
8.5) Transistors have 3 pins to keep straight. Don't screw them up either.

9) The tuner section, and particularly the moving parts of the variable capacitor are not to be trifled with. In particular, don't let the red straw of the Deoxit can come off around it (http://www.audiokarma.org/forums/showpost.php?p=4299850&postcount=146)

Do I have most of this right? Is there anything else I should know before I start contemplating a Mouser order? How much solder wick am I going to go through?

Sorry I didn't respond while it was still yesterday. I was at the Indians game at Fenway Park.
 
Also, a huge thanks for your help and particularly for putting that cap list together. I've seen it in probably a dozen threads by now.

I'm going to distill it down to a Mouser part number/count list tomorrow to facilitate ordering and I'll put that up once I do so.

Thanks also for bearing with me while I learn a few things about the world of analog.
 
Skip the Gold, just deoxit and faderlube.

Other corrections to follow when I have time to type. Overall: close...
 
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Awesome, thanks, that'll save $15. Should I use anything on the switches and other contacts after I clean them or just leave them be?
 
moped said:
Awesome, thanks, that'll save $15. Should I use anything on the switches and other contacts after I clean them or just leave them be?
Click to expand...

A quick shot of faderlube... you are washing out the old lube when doing the deoxiting, new lube won't hurt...
 
OK, here's a list of part numbers and quantities based on your list for everybody's ordering pleasure:

Code: 
647-UPW2A102MHD     1
647-UPW1E470MDD     3
647-UVZ1J682MRD     2
647-UPW1C471MPD     2
647-UPW1H100MDD     4
647-UPW1J221MPD6    1
647-UPW1H101MPD     4
647-UKL1H2R2MDDANA  8
647-UKL1H3R3KDDANA  2
647-UPW1V101MPD     3
598-DSF050J474      4
647-UPW1V220MDD     4
647-UPW1A101MDD     2
647-UPW1V221MPD     4
647-UPW1H4R7MDD     6
647-UPW1H470MED     4
647-UPW1A221MED     3
647-UPW1H010MDD     3
647-UPW1E331MPD6    1
That should be 61 caps in all
 
And if you're curious, here's the code I used to generate the list above:
Code: 
# runs before any lines are processed
BEGIN {
    # initialize the per-line cap count
    caps = 0;
}

# skip comments (lines starting with a # character
/^#/ {
    next;
}

# skip blank lines 
/^[\t\f ]*$/ {
    next;
}

# anything left should be a line listing a capacitor
{
    # The part number is field 6 (1 based counting in awk)
    # if we've already seen this part number, it's in the counts array, increase
    # the count.
    if ($6 in counts) {
        ++counts[$6];
    } else {
        # otherwise initialize an element in the counts array to 1 to account
        # for this line.
        counts[$6] = 1;
    }

    # increment the line count
    ++caps;
}

END {
    # we'll use this to re-tally the total number of capacitors as a sanity
    # check.
    check_caps = 0;

    # display a list of part numbers and quantities (counts)
    for (pn in counts) {
        print pn "\t" counts[pn];
        check_caps += counts[pn];
    }

    # Sanity check.  Does the per-line count and the total of the per-cap
    # counts match?  They'd better.
    if (caps != check_caps) {
        print "capacitor counts " caps " " check_caps " don't match";
        exit 1;
    }
}

This is awk code, which I ran under gawk. YMMV with other awks. If you have no idea what awk is, or run Windows(1), don't worry, this has nothing to do with stereo equipment and you can ignore this completely.

Otherwise feel free to use this to turn per-component parts lists into a condensed list for creating an order. Comment out any non-blank lines that don't list a capacitor by inserting a # character at the very beginning of the line.

(1) Yes, I know about both cygwin and the native Win32 build of the unix utilities. If you know about them too, you probably already know that that comment wasn't for you.
 
I have good reasons to leave the BOM at one line per component.

Plus the mouser site happily gobbles the single line per component BOM up and does exactly that, NOT showing multiple lines of the same component, but consolidating them.

Just contol-c copy and paste the text block into Mouser's BOM entry page/tool "Import Bill of Materials (BOM)" under the Services & Tools tab after you have logged in.

Plus I made my LIVING doing code and hardware at the ragged interface where the difference between the two blurs. You would not believe the frontiers and industries I have been involved with since the 70's... Military, Banking, Phone, ISP, Typesetting, Electronic component manufacture, Industrial Packaging Automation, Medical (including Nuclear) and Consumer Electronics.

I KNEW PLC controllers were very very vulnerable long before ANYBODY ever heard of the Stuxnet virus. Hard coded passwords and "secret" factory back doors, my @##....
 
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Here's where I confess to never having ordered anything from the Mouser site before and not knowing you can import a BOM directly. I've always worked somewhat towards the software side of that ragged edge of which you speak ;)

Anyway, no intent to offend, was trying to do something useful (but apparently unnecessary) with what I do know, because I don't know anything about electronics and don't have anything to contribute on that end yet.

I picked up some deoxit and faderlube yesterday at my local Guitar Center, but I'm probably not going to get a chance to give the receiver a going-over until sometime Sunday. I'll post once I know whether it's done any good or not.
 
I went and Deoxited the receiver, and I have to say: wow, getting to the pots and switches is a royal pain.

Pulling the front panel off wasn't bad, but then actually getting the board out without breaking anything was kind of a trick. I had to unmount the head amp and power supply boards from their standoffs to get enough clearance to get the board with the controls on it out. There were a couple of wires that were only barely long enough to get the stems of the pots clear of the holes. I think I spent more time getting to the controls than actually cleaning them.

The good news is, it was all worth it! The crackling is now gone :banana:

I have to admit to being a little skeptical that the crackling could be down to just dirty contacts, and that fixing it would be as simple as a spray can, but I'm a believer now. That Deoxit is good stuff.

Thanks for prodding me to do the cleaning job first! Doing so was highly worthwhile, and I'll know a little bit more about how this thing comes apart and goes back together when I recap it. In the meantime, I can listen to music crackle-free.
 
Hi Everyone -
I am in exactly this situ right now as described by OP -
super scratchy/crackle pop happening on left channel -
I am going to try doing the cleaning job first -
I am a bit nervous about removing the various boards to get to the controls - does anyone have any tips?

Thanks in advance for any insight on this process - this is a very special receiver to me and I really want to get her back up and running again!
Reed
 
well - I went in -- hopefully this was the right way to approach accessing the pots --
my plan is to deoxit the pots next --

am I on the right path?

Thanks!
 

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rmunson said:
well - I went in -- hopefully this was the right way to approach accessing the pots --
my plan is to deoxit the pots next --

am I on the right path?

Thanks!
Click to expand...

yup - looks good. you can turn the unit over on its top and work from the bottom. Becareful with the dial pointer when you are handling it.

let us know how you make out.
 
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