My SX-939 Shoots Lightning! (help)

xoted

Member
Well it's across the speaker protection relay.

Her'e s the back story. About four years ago, I helped an 87 year old friend organize his garage and he gave a 939 to me for my time. I like any electronic gear and immediately opened it up to check out the insides and clean it. What the hey, I took electronics for a couple of years in Jr. High, and back then I new everything.

The power supply board looked a little toasted around what I'm guessing are the power transistors and heat sink. (D313D and B507D) Some of the resistors don't look as if they were cool dudes either and probably will need to be replaced.

I found the caps next to the transformers were biblical, I mean they were hole-y OK had holes and the magic juice leaked out. Purchased a set of 10,000 uf caps with a higher temperature rating, as that was the only way to hop it up, and installed it -- after -- I took a pictures of the wiring. Memory isn't as good as Jr High.

It worked! And it worked very well powering a set of Acoustat IIs. Then one day an oldies radio station played Peggy Lee singing Fever, and I melted. Never had a stereo I owned have an effect on me. However, it only worked for about three months after that repair. That was over three years ago.

What hadn't been mentioned was that someone had gotten to the machine before me and released some magic smoke, unless Pioneer solders the top half of the fuses to the holders on the power supply board, and some of the wound wiring was soldered to posts, and some solder didn't have the same oxidation as the (I assume) original solder job.

The system's symptoms were popping sound coming from the speakers, loss of a channel, return of the channel, more popping or arcing across the relay (could it be that the relay wanted to be a set of points in an old Chevy?) Then nothing but popping.

So I scanned some of the threads, and found a request for the following information, and have supplied the info below. FWIW, I was using my Jr High RS Micronta VOM and a cheap Harbor Fright digital multi-meter,which can be replaced if the 939 can be user serviced or if someone needs more accurate information.

Here's the info. The 939 stuff is in italics:

<<The protection board is marked " awm-062", and you need to measure the DC voltages on pins :

pin 11, +35v; 33-34.8
pin 2 -13v; -14

pin 1 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Varied all over the place when the protection circuit was fired.

pin 3 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Also varied all over the place when the protection circuit was fired.

pin 12 is the exception, you need to read the AC voltage here, about 7.5 volts AC. Mine 7.5

ok turn the meter back to DC for the rest of the readings.

ALL readings are taken with the red lead while the black lead of the meter is connected to a metal chassis ground.

The boards are accessed through the bottom of the unit.

Then read the power supply voltages on the power supply board marked: "awr-052" right next to the protection board.

The readings taken by me are listed below in italics.

pin 8 +25v 24.7
pin 6 +47.5v 45
pin 5 +35v 34
pin 11 -25v -25
pin 9 -43v -44
pin 10 -13v -14
pin 4 +13v +13
pin 2 +7.5v +7.95<<

The questions are: can a relative newbie who just built a small JFET pre-amp and enjoys figuring things out, and making things in general, and fixing things, repair this 939 problem?

Am also planning on making a LM3886 stereo from parts and build on it as a hobby through others who've come up with enhancements. I'm not afraid of longer term projects.

If not, any ideas on how much repairs would cost (I'm in the greater L.A. area.
 
pin 1 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Varied all over the place when the protection circuit was fired.

pin 3 amplifier output, could be as low as 10 millivolts, or as much as + or - 35v: Also varied all over the place when the protection circuit was fired.

common channel problems in the amp point to power supply problems.

That said, the 939 has some problematic transistors in the power amp section, and could be affecting the power supply.

It has both 2sa726's as well as 2sc1451's. It could benefit from a power supply and protection "rebuild" with (mostly) fresh transistors and caps as well.
The 2sc1451 when they blow turn the power output section into a smoking ruin

The recap list has the caps, but not the transistors explicitly spelled out.

if you're game, it would involve replacing electrolytic capacitors, and a handful of transistors - which we would specify for you.
most of the transistors will be about 15c each, a few are closer to under a buck
8 on the power amp (4 per channel, 4 trimpots too) mandatory
anywhere from 2 (mandatory q6>ksc2383, q7>ksc2690) through 6 (q1-4 >ksc1845) on the protection assembly
6 on the power supply mandatory


for better sound, and some reliability (have 2sa725/2sa726 troublemakers > ksa992, 2sc1312/2sc1313 > ksc1845):
8 on the control amp (4 per channel)
8 on the phono amp (4 per channel)


Now, old lists exist, with some sub-optimal transistor choices (NO D1616's!! or 733's for example) so when the list in this thread is "complete" I will sign off on it IN THIS THREAD.
As I am busier than a cat in a room full of rocking chairs, it won't be instantly...
 
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Thank you!

Markthefixer,

If you've got the patience - I've got the time, and the desire to larn me some stuff!

You spec it and I'll follow instructions. The job is worth doing so let's do it correctly & completely; using the best parts that will give it the most accurate and pleasing sound. I'm not building something for resale.

In searching the forums before asking for help, I've seen you helping others with similar problems. Thank you for the knowledge you've shared with others and with me. I'm also grateful you've included me in your group.

While I'm cooling my heals, I have some questions:

I've got two soldering irons (20W) and a soldering gun, do you think it's time for a adjustable digital temperature station? Any suggestions/specs on brands or attachments?

Regarding my VOM. The Orvac guy who helped me with other projects recommended a Klein Tools MM200 Auto Ranging Multi-meter, though I'd like to get a Klein 1000 or 2000 to grow into, in case this addiction takes off. While buying cheap is a false economy, I do want to be judicious in my asset allocation.

Does AudioKarma have a parts supplier who supports this board that deserves my loyalty?

Lastly, no need to rush for me. I'll be going slow, and if I catch up then I'll start on that LM3886TF chip amp project. It's one of the benefits of ADD. :)

But, and most importantly: What would you like me to start on first?

Thank you again.
 
Here's thread on the 939 I did 2-1/4 years ago. This one is listed in the PIONEER BOM PARTS LIST Thread by Socal. It's the last 939 that has been done. You should get some idea of what you are getting into.

http://www.audiokarma.org/forums/showthread.php?t=494501

The info in this thread needs to be transferred to your copy of the service manual. It concerns the CORRECT Bias voltage for the 939.

http://www.audiokarma.org/forums/showthread.php?t=512271

General Info on replacing Transistors and identification of the pins. REPLACEMENTS are NOT pinned the same as the originals. Pay particular attention to POST #11 and print the jpg's. http://www.audiokarma.org/forums/showthread.php?t=43186

I'd start on the POWER SUPPLY 1st. Nothing works right without it running right. Then the protection board and relay replacement, MAIN AMP BOARD, then the various tone, and preamps going back from the MAIN AMP. TEST the UNIT for operability at minimum after each board.
 
Thank you Larry

Thank you for sharing your ordeal. I can empathize as it looks like my pattern of behavior. I'm planning on taking my time, and judging by your experience (roughly four months from first to last post) a long time. Unfortunately, I'm a nube at this.

Part of this is planning for an early retirement (also called Fantasy-land) where I'd like to repair bicycles and have a higher end stereo shop with repairs. I actually enjoy figuring out what is wrong and fixing things. Kind of like puzzles.

I hope you don't mind if I ask questions when comparing Mark's and your parts lists. At that time, I may prefer the ones that shoot out the green vs. orange sparks as I err. :D

I've already checked the power supply board and found a couple of slightly bulging caps, so I can see that it's wise to replace as many caps as possible. It's no different than when I changed the front seals and tension wheel concurrently with the timing belt on my car. You've got it open so do it all at the same time and be done with it.

After my bike ride, I'm taking pictures. Lots of pictures, and storing them in multiple locations. Then it's removing the solder from the fuses, it's simple and just looks wrong.

After that it's searching, making, and organizing a browser links folder of all of the 939 repairs listed on AK, with keywords. I previously viewed the bias voltage issue and was wondering how long it would take to find it again. Thank you for providing the links and additional information.
 
After reading the posts checking the schematics

Was this noob ever off. Check out the picture of what I thought was wrong. It's he power supply circuit.

20150502_122153.jpg

Think it's salvageable?
 
Yes,it's been hot but will work. Rebuild the entire board, caps, transistors, and diodes.
Soldered fuses is a new one
 
Thanks

Thank you for taking a look.

Yup the solder-sucker and wick both got a workout. Ground has been broken! :D
 
Hoo- Boy!!! Has that P.S. been BAR-B-Q'ed!!!!! Don't take any chances on that one. I'd replace ALL transistors, caps, diodes, AND resistors on this board. With regard to transistors on heatsinks, make sure the Heatsink grease you use is NON-CONDUCTIVE! Be very careful on the underside as the circuit traces may be lifted off the board.

Also raise resistors approx 1/4-3/8" off the board to increase airflow around them and minimize further heat-soak on the board.

As for differences between MTF's lists and my lists, you'll find out sooner or later that MTF is the source for 99.9999999999999999999999999999999940% (Ivory soap pure) of the parts lists on the PIONEER Forum. This is the case here. His research and experience on the forum is extensive and pretty much untouchable when it comes to PIONEERS.

Go slow, do exactly as Mark suggests, and don't get ahead of him. He spends a lot of time on here helping out people, but that time can be limited per person at any one time. At the top of the forum (PIONEER, DIY, General Audio) are sticky threads. These are threads that have useful info on different topics, like DeOxt use, how to test Bi-polar Junction Transistors, PIONEER Tuning Fork Guides, etc. Download the info (particularly the Tuning Fork Guides, and the Bi-polar Junction Transistor info from post #11 and further). There are other threads, but these are the one's I can remember without going over to the forums).

A 20w iron is a bit weak. A 30-45w Weller iron will work fine. Rosin Flux, a de-soldering tool (syringe type if not doing many units or vacuum pump type if doing many in short time), De-Soldering Braid, and Rosin core solder. Never use Acid core solder (plumbing solder) on Electronics.

Wire wrap connections DO NOT get unwrapped. A special tool and schooling to use it are required to be able to wire wrap. The wire gets nicked at each corner as it's stretched around the pin, which gives an air tight connection. Best to just de-solder the pin from the board. If the wire breaks, go ahead and strip off enough cover to wrap the wire around the pin and solder it on. PIONEER used solid core wire which is brittle upon flexing.

You don't need to remove any of the boards. You will need to move them enough to work on them. There are wire ties and hold downs around the bundles. Open them up and make slack in the bundles, THEN move the board.

When replacing parts, remove 1 part at a time and replace it. Then move on to the next part. When you get the whole board done, TEST THE UNIT. Do this for each board. It makes finding mistakes easier, and limits it to one board.

Build a DBT (DIM BULB TESTER). This is basically an incandescent light bulb (NO Florescents, cfl's, leds, or Halogens) that is wired in series and serves as a current limiter and helps keep the majic smoke in. You'll need a 40W, 60W, 75W,& 100W bulb for most units. Larger amps, and receivers will need up to 200W. Google it and you'll get a bunch of links.

I would blow up the board pictures in the manual, mount on the wall above your bench. Also the main schematic. It helps a lot more than scrolling all over a CRT or lcd screen.

The 939 is a pretty good receiver. I actually like mine better than my old SX-1010. At 1st glance it can be a bit daunting. Taking it one board at a time reduces the overall retisence to working on it. Go slow, methodically, and if you run into a problem....STOP....post the problem, and get some help for it. If you don't understand something, ASK QUESTIONS.

Good Luck. I'll be around. It may take a day or so sometimes to answer.

Larry
 
Thanks!

Larry,

Yup, it was Pioneer's first attempt at a dual use stereo/cooking appliance probably marketed by Ronco and Ron Popeil! :yes:

Thanks for the guidance, confirmation I'm going about this correctly, and encouragement.

Got a little intimidated when rebuilding the entire board was suggested. A few transistors (after checking and rechecking ECB) and capacitors (+/-) that are easy to spot is one thing, the entire board of 50 +/- parts is another. More so when some resistors are baked (hard to read). But went to the manual and saw I've got lots of tools to help, and now support from people in this forum . . . all is well with the world.

What do you think about bread-boarding the parts prior to installation? That reads awful, hope I don't have parts activists picketing my posts.:D

I have a schematic (~34" x ~40") that came with the manual from the original owner that's going to Kinko's this week to be digitized and blown up. That was a great idea, thanks! I was getting worried about folding and unfolding it multiple times.

If the format is editable, I'll clean up the folds, but either way I'll post the file as a way to return the favor for the next person. It's much cleaner than what I've been able to download.

If someone knows the preferred file formats for schematics, I'll see if it can be provided. I'll post it but with the limited memory we're allowed, I'd rather a moderator include it in a SX-939 all-in-one sticky.

Steve
 
Send the schematic to the AK DATABASE admins and ask to have it included with the sx-939 manual. That's the easiest way, and you can eventually link to it.

Bread-boarding up to you. Big time bloating. especially with subsequent water ingestion.

Take each board one part at a time. Sure some of them look daunting, but go ahead and break it down into sections if you need to.
 
Hey Larry!

I found a post of yours trying to help a noob with a 3A 250 V fuse in his system. I think I may know why, and then the reason why mine were soldered in.

It's hard to find a 125V cartridge fuses that fit a length from 37mm (outside) to 25mm (inside of the clip) dimensions for 1 & 3 amps.

Even the great google couldn't come up with a cross reference for AAX-010(or 008)-0 fuses. I'll wait for MTF to give guidance on what would either work or look good, such as fuses with axial leads.

Thought you might want to clear up one of the great life-mysteries that you pondered deeply at one time. :scratch2:
 
Another Factoid

Or another potential clue:

While spending time examining the SX-939, it looks like the transformer was replaced somewhere along the way. It currently has an ATT 167, A-AS-TLK transformer installed. Perhaps that's another clue to the system's issues.

Should I replace it with a Torroidal? It would give it that cool "The Robot" look from the original Lost in Space series? :yes:
 
I use 250V AGC Buss Brand or similar Fuses. The 250V is just the Max Voltage they can handle.

The AAT-167 is the specified Transformer. It could have been replaced, or just been pulled and checked internally. Check the voltages on the secondary side and compare them with the schematic.
 
Transformer Check

Hi Larry,

Could you please confirm that the transformer is an AAT-167? Mine reads "ATT-167."
 
Transformer

Thank you. Now I can look up the parts myself, and make preliminary bull of materials until it's my turn with MTF.

I like the quote, "Give a man a fish he eats for a day, teach him to fish and he feed himself for a lifetime." I'm larnin mi sum gud stuff!

As an aside, it's amazing how much time it can take - just to build an order. I now understand the value added (and charged) for kits with all their parts. This will give me a head start.
 
By PM ( :no: )
xoted said:
Hello Mark,

Thanks again for taking me under your wing.

During my waiting period, in fooling around with the unit, I made a discovery. I posted a picture of my overheated power board, and got suggestions to rebuild it.

Should I wait for my turn with you or should I just go down the parts list in the manual, order them, and start rebuilding the board on my own?

Either way works for me, as somehow projects multiply like rabbits for me.

Thank you for your time, and please believe that in no way am I trying to rush you.

Take care.
response to PM:

make the list using Larry's list as your starting point,

THEN LIST it here - DON'T order it - and wait for confirmation -

it's easier to check and make changes than to start from scratch.

It's also easier to NOT buy any wrong parts, and have to reorder the correct parts.

list the power supply transistors and diodes, the protection transistors and diodes and the power amplifier transistors and diodes. then look for all those bad transistor numbers I warned you about, and list them too (wherever they are in it). THAT will take you some time.

I can make some off the cuff power supply, power amp and protection transistor observations that will be cryptic and succinct, and will confuse the hell out of you. So save me all the typing and do the transistor lists, along with that cap list in the thread Larry linked to.

I was busier than a cat in a room full of rocking chairs, then my chair broke and wasn't / isnt a simple fix (even the replacement parts needed to be modded/improved - crappy chinese welding!!), I busted my car's drivers window during a fall in the mud during a rainstorm (and wound up SOAKED with a zillion small cuts) SEPARATELY caught three stitches in my thumb with a sawzall working on that chair (cut since closed up and self removed stitches). And an issue I expected to be put to bed for the season has reared it's ugly head with THREE minor events (one of which caught me the busted car window) and one MAJOR event a week from Saturday.
 
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939 Power Supply BOM

Hi Mark,

I'm sorry you hit a bump as you slid down the razor blade of life. Ouch.

To keep it simple and orderly, I'm posting only my first project, the power supply board, with everything from the manual accompanied by Larry's learnings :)))as a cross reference where they were available.

A word document is attached as it's a cleaner presentation than what my knowledge of the forum's system can produce, and it might be better for the next person in line to use. I'll compile it into a total document at the project completion.


SX-939
Parts List of Power Supply Circuit Assembly (AWR-052-0)
CAPACITORS
Symbol Description uF Part No. Cross Reference Larry
C1 Ceramic 0.01 150V ACG-004-O
C2 Ceramic 0.01 150V ACG-004-0
C3 Ceramic 0.01 150V ACG-004-0
C4 Ceramic 0.01 150V ACG-004-O
C5 Ceramic 0.01 150V ACG-004-0
C6 Ceramic 0.01 150V ACG-004-0

C7 Ceramic 0.01 150V ACG-004-0
C8 Ceramic 0.01 150V ACG-004-0
C9 Ceramic 0.01 150V ACG-004-0
C10 Ceramic 0.01 150V ACG -004-0

C11 Electrolytic 47 63V CEA 470P 63 UPW2A470MPD
C12 Electrolytic 47 50V CEA 470P 50 UPW2A470MPD
C13 Electrolytic 470 50V ACH-038-0 647-UPW2A471MHD
C14 Electrolytic 470 80V ACH-038-0 647-UPW2A471MHD
C15 Electrolytic 100 63V CEA 101P63 647-UPW1J101MPD

C16 Electrolytic 100 63V CEA 101P63 647-UPW1J101MPD
C17 Electrolytic 47 16V CEA 470P 16 647-UPW1E470MDD
C18 Electrolytic 47 16V CEA 470P 16 647-UPW1E470MDD
C19 Ceramic 0.001 50V CKDYF 102Z 50
C20 Ceramic 0.001 50V CKDYF 102Z 50

C21 Electrolytic 47 50V CEA 470P 50 647-UPW2A470MPD
C22 Electrolytic 2,200 10V CEA 222P 10 647-UPW1A222MHD
C23 Electrolytic 220 16V CEA 221P 16 647-UPW1C221MPD
C24 Electrolytic 1,000 35V AC H-039-0 647-UPW1V102MHD

Mark The Fixer's Cap rules of thumb (nichicon)

I use upw, uhe for general caps including signal coupling in that order depending upon stock "cea"
I use ues, uep & uvp in that order for bipolar depending on stock
I use ukl for low leakage caps (in sensitive areas they reduce the noise floor)"ceanl", "cssa", "csza"
0.1uf to 2 uf I use stacked film where they fit: DFS and ECQ

solid aluminum and tantalum caps get stacked film when possible, or ukl's otherwise. "cssa" "csza"

c?B means it's an axial cap = one lead on each end
c?a = radial = both leads on one end

RESISTORS
Symbol Description ohm Part No.
R1 Carbon film 1.5k RD ¼ PS 152J
R2 Carbon film 1.5k RD ¼ PS 152J
R3 Carbon film 1.5k RD ¼ PS 152J
R4 Carbon film 1.5k RD ¼ PS 152J
R5 Carbon film 12k RD ¼ PS 123J

R6 Carbon film 11k RD ¼ PS 113J
R7 Carbon film 5.1k RD ¼ PS 512J
R8 Carbon film 5.1k RD ¼ PS 512J
R9 Carbon film 5.6k ½ W RD ¼ PS 562J
R10 Metal oxide 2.7k 1W RS1P 272J

R11 Metal oxide 820 2W RS2P 821J
R12 Metal oxide 820 2W RS2P 821J
R13 Carbon film 33 RD ¼ PS 330J
R14 Carbon film 33 RD ¼ PS 330J
R15 Carbon film 10k RD ¼ PS 103J

R16 Carbon film 2.7k RD ¼ PS 272J
R17 Carbon film 150 ½ W RD ½ PS 151J
R18 Carbon film 33 RD ¼ PS 330J
R19 Carbon film 33 RD ¼ PS 330J
R20 Carbon film 4.7k ½W RD ½ PS 472J

R21 Carbon film 3.3 RD ¼ PS 3R3J

SEMICONDUCTORS
Symbol Description Part No. Larry Replacement

Q1 Transistor 2SD313P-E or D KSC2073
Q2 Transistor 2SC1318-Q or R
Q3 Transistor 2SC1318-Q or R
Q4 Transistor 2SB507P-E or D KSA940
Q5 Transistor 2SA720-Q or A

Q6 Transistor 2SD313-E or D KSC2073

D1 Diode SIB01-04 1n4007
D2 Diode SIBO1-04 1n4007
D3 Diode SIB01-04 1n4007
D4 Diode SIBO1-04 1n4007
D5 Diode SR3AM-8

D6 Diode SR3AM-8
D7 Diode SR3AM-8
D8 Diode SR3AM-8
D9 Diode 1S1885
(SIBOl-01) 1n4007 ?
D10 Diode 1S1885
(SIBO1-01) 1n4007 ?

D11 Diode 1S1885
(SIBO1-01) 1n4007 ?
D12 Zener diode WZ-130
D13 Zener diode WZ-130
D14 Zener diode WZ-140


Please let me know:
If I can post your rules in the 939SX BOM, and if the word doc format works for you or is a good idea.

I eagerly await you next instructions, but don't rush. I've got family moving to the San Diego area from Chicago, and have been helping when needed. It's only about a 200 mile, from my place - RT each time, but it's with L.A. to S.D. traffic, ugh.
 

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