• Please note that Audiokarma will be offline briefly for updates early on Monday morning, September 28th.

Pioneer SX 434 No Sound

S

sevarre

New Member
Hi All,

I hate to make a new thread about the Pioneer SX 434 as there seems to be so many, but I am stuck a moment in my repair process and I would like to be able to revitalize this unit without having to take it to a shop (and certainly without having to throw it out, particularly because I spent I spent like 90 bucks on it on eBay a few years ago when I wasn't so wise- it was working then).

I've pretty much searched every 434 thread on this forum and have the service manual (the information present is so insanely wonderful- thank you all for you contributions). The thread that describes my situation the most is the following:

http://audiokarma.org/forums/index.php?threads/pioneer-sx-434-repair.243180/

Fuses F5 and F6 on (AWR-062) blow and I've followed the advice of "ecluser" and disconnected the +24V pin on pin 25 of the power amp AND the -24V wires at pin 23 and pin 28. The fuses do NOT blow after doing this, so I'm assuming this means there's some issue on the amp board?

When testing with my DMM on the diode function from (+) on 28 and (-) on 25 I get .745 (the reverse is OL) and when I test (+) on 23 and (-) on 25 I get .763 (the reverse is OL). So, these seem like normal diode/transistor drops, correct? Maybe the short (or whatever the error is) is on the other side of the amp board?

A few months ago I purchased a few transistors in the hopes that those might be at fault, but all the transistors I've checked so far don't seem to be at fault. I've checked transistors Q1, Q2, Q3, Q4 on AWK-034 (all 2SC1344) and they all seem to behave normally after taking them out of the PCB (reading of like .930 from collector/emitter (-) to base (+) for an NPN so that should be good, right?). The current parts I have are:

KSC1845FTA for 2SC1344
KSC2690AYS for 2SC1318
KSA992FBU for 2SA725

I don't have replacements for 2SA720R or 2SB507D yet. I have "two.dogs" part list conversion for the AWK-034 (thank YOU, so helpful), so I have an idea of what parts I will need to order from mouser.

Any help would be so beneficial to me. I really don't want to have to buy all the components for the AWK-034 and have to resolder them on to the board in order for this to work. But, if I can't identify the actual component problem, that is probably what I will do.
 
Register to hide this ad
Hi, l would start by removing the output transistors q20-23 and check these by using the 6 way test, then work backwards through driver transistors q16-19 and if necessary pre-drivers q14-15. You will have to remove any transistors to test as they cannot be checked in circuit. Also may be worth checking any diodes on that board.
If you search here on AK for transistor (or diode) 6 way test there are some really good write ups on this subject.
http://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/
Hope this helps.
 
Last edited:
I'm with OldSansui on testing the output's 1st....OUT OF THE UNIT. Any Transistors to be replaced NOTE the Leg orientation on the old one. And then pull the DATA SHEET for the new one. The orientation will be different on the TO-92 size (ksa992) but the TO-126 and TO-220 should be the same. CHECK ANYWAY.

I found my parts list for the POWER SUPPLY and the AMP SECTION of the Main board. This is the list I used back in 2010 so double check and make sure all parts needed are available @ mouser.
Power Supply (all electrolytics and semiconductors)
C7 330 50 647-UPW1H331MPD
C8 100 50 647-UPW1H101MPD
C9 100 25 647-UPW1E101MED
C10 100 35 647-UPW1V101MPD1TD
C11 100 16 647-UPW1C101MED
C12 220 16 647-UPW1C221MPD
Q1 2SC1384R 512-KSC2690AYS
Q2 2SC945R 512-KSC945CGTA
Q3 2SD313D 512-KSC2073TU
D1-5 S1B01-02 512-UF4004
D6 WZ-140 78-1N5244B


Power Amp (SA720 and 725, output transistors, emitter resistors)
R83-6 0.5 2W 71-CA0002R5000KE14
Q10-11-12-13 2SA725g 512-KSA992FBU
Q18-19 2SA720R 512-KSA1013YBU
Q20-21 2SD313D 512-KSC2073TU
Q22-23 2SB507D 512-KSA940


BOM LIST
647-UPW1H331MPD
647-UPW1H101MPD
647-UPW1E101MED
647-UPW1V101MPD1TD
647-UPW1C101MED
647-UPW1C221MPD
512-KSC2690AYS | 10
512-KSC2073TU | 4
78-1N5244B | 2
512-KSA992FBU | 20
512-KSA1013YBU | 4
512-KSC2073TU | 4
71-CA0002R5000KE14 | 4
512-UF4004 | 4

The numeral after the | is the QTY. Copy the BOM list to mouser's BOM builder and you've now got a order list you can name. The Number of ksa992's is so you can MATCH THEM for hFe on your DMM (should it have that capability)

Larry
 
I forgot to say, when you pull the outputs to check, keep note of which came from where so that if you find one or two shorted ''which im guessing you will'' then you will know which channel drivers etc to check.
Larry made a great point about leg orientation old vs new.
 
Awesome, than you Oldsansui441 and larryderouin for the replies! I will try testing the output transistors (when I get some time) using the 6 way test first and then proceed from there and let you know what I find.
 
Wow, sorry this has taken so long to finally get back on this- things have been kind of hectic recently. I really do appreciate the help.

I found resistor Q23 (2SB507) to be bad; collector and emitter are shorted, and I get a reading when (-) on emitter/collector and (+) on base. The other three output transistors seem to be fine. I took them all out the circuit as instructed. So, looks like I might want to be checking Q19, Q15, and Q11 next?

I've ordered all the parts, so if I find any of them are bad I can replace them right away! They should be here this Friday. Unfortunately, the emitter resistors (71-CA0002R5000KE14) are back ordered until Jan 2017 (wow!). Is this normal? Do you think these resistors are crucial to replace?
 
If the resistors measure correctly (low ohms, your meter may not be able to read a sub ohm resistor correctly) I would not replace them.
 
Whenever I have an older unit without a speaker protection relay that has no sound, and no popped fuses, the first thing I check is the regulated power supply voltages. Even with a tits-up output transistor, you should still get sound on a cap-coupled amplifier.
 
Got the parts and replaced the suspect transistor. When I was inspecting the amp board, though, I noticed one the caps was actually disconnected from the board- one of it's leads was no longer attached to the capacitor body at all and looked like it was rusted out or something. It is one of the 220uf 25v ones, so it's gotta be either C51, C52, or C57 (I will give it a closer look so I can determine which one it actually is). I don't have a replacement part for this, so I will try and get one at a local radioshack tomorrow so I can get this thing going!

ryuuoh said:
If the resistors measure correctly (low ohms, your meter may not be able to read a sub ohm resistor correctly) I would not replace them.
Click to expand...

Yeah, that's what I was thinking. I don't think my meter can measure resistances of that low a value. I found a circuit to make in order to test low resistance resistors, so I might try to do that.

tarior said:
Whenever I have an older unit without a speaker protection relay that has no sound, and no popped fuses, the first thing I check is the regulated power supply voltages. Even with a tits-up output transistor, you should still get sound on a cap-coupled amplifier.
Click to expand...

The fuses do pop when the whole thing is hooked up the way it's supposed to be. They don't pop only because I've disconnected the power supply circuit from the amp assembly.
 
Nope, I found Q19 to be working properly. In fact, the only transistor on the amp board that I found to be faulty was Q23 (the only ones I didn't check were Q5 and Q6). Sorry to say, I hastily went ahead and tried powering up the unit after replacing the four output transistors and C57 (the bad cap I found earlier). Everything was going fine and I was actually able to play some music, but at some point it stopped working (I went upstairs to get a celebratory drink and by the time I came back down, the audio was gone, DOH!). So yeah, pretty sloppy- I won't make that mistake again.

Same fuses are blown, but this time Q20, Q21, and Q22 went bad- Q23 tested fine still. When I was going through and troubleshooting the board again, I noticed that C51 was now disconnected from the circuit. I'm not sure if I missed that it was disconnected before or if it happened as a result of me powering up the unit again... regardless, I've decided to recap all the electrolytics on awk-034. Curiously C51 is the same cap as C57 and also connected to ground (pin 22). I intend to replace all transistors on awk-034 before powering up again (besides Q5 and Q6- don't really think I need to?).

I found the cap list for awk-034 in the digital docs section. The replacements listed for CSSA R33M 25 (C23 and C24) and CSSA R47M 25 (C35-38) were both obsolete. I ordered 647-UKL1HR33KDDANA and 647-UKL2AR47KDD, respectively. Hopefully these work! I also threw the replacements for the main filter caps on there in case I decide to replace those later.

Thanks for getting me on the right track!
 
Nichicon ukl's are a good choice for cssa replacements. Sounds like you have made the right decision in replacing all transistors and caps on that board.
ON semi are good for the outputs and Fairchild for the rest of the transistors.
Once again just remember to check all resistors and diodes on that board also.
All the best with it.
 
Sansui; The output's on the SX434 are TO-220's. So either Fairchilds or Onsemi's would be a good bet. Fairchilds are usually a little less than OnSemi's in most cases. IT's one of those 6 of 1, 1/2 dozen the other cases.
 
Ahh TO-220's, thanks for clearing that up Larry, yep makes sense, l was thinking low powered TO-3 package, just shows l haven't done a 434 yet, haha.
 
The above sounds too familiar, as I have been trying to get a 434 back up and running. Found the same output transistor bad, replaced a bunch of stuff, and it worked!!! Left it on and ran out for awhile when I returned, it was dead...Now I don't know where to start... My dmm doesn't measure resistors nicely...I've had so many dmm's and they all fall short---I'm shopping for a fluke 117 now....Did Sevarre ever get his going?
 
Unfortunately, mine is not up and running yet. I was hoping to have it done before New Year's, but I had too much other stuff going on (or I was just lazy? depends on how you look at it, hah).

I have replaced almost all of the transistors and electrolytic caps on AWK-034 and AWR-062. I still need to check and replace the diodes and resistors on those boards. I know I need to take the resistors out of the board to properly check them, but I have been able to get resistance measurements that jibe with the resistor's rating, so I might forgo taking every single resistor out and checking it. Plus, my soldering skills are not too great yet, so I fear I might just mess up the board by taking out and replacing every resistor.

I have NOT powered the unit back up yet. I am waiting on some emitter resistors from mouser at the moment (should be here in two weeks). I plan on getting everything ready for a power up by the end of this month.

What dmm are you using? I've been using an old Fluke 8021B and it seems to be working pretty great. I was able to read the 0.5 ohms on some of the emitter resistors, but I'm not sure if it was just luck that it showed 0.5 ohms or not. Those new dmm's seem pretty nice, but you could potentially pick up an old Fluke on the cheap at a second hand shop/thrift store if you are looking to save money. However, I suppose a new dmm would be a good investment if you plan on doing this a lot. Plus, it would be cool to have a built in capacitance measurement.
 
My dmm is an amprobe without an auto-range feature. I'm new at this also, and my soldering skills are weak...I have found solder wick to be much more effective to remove components than a "solder sucker"... some of the solder pads have already lifted from the board but are still intact...I too am concerned I may mess the board up. Thanks for your update...keep us posted on your findings, and I will do the same. I also have gotten resistance readings that jibe, but have about 20 that are way off, maybe because they are in the circuit...?
 
sevarre said:
but I have been able to get resistance measurements that jibe with the resistor's rating, so I might forgo taking every single resistor out and checking it. Plus, my soldering skills are not too great yet, so I fear I might just mess up the board by taking out and replacing every resistor.
Click to expand...

Yes good call, if they test fine IN circuit then leave them, if they test out of spec in circuit then pull them or raise one leg and re test, depending where they are in the circuit they will always test out of spec.
 
You must log in or register to reply here.
Back
Top Bottom