Pioneer SX 434 No Sound

[jagrunst]

UPDATE: SX-434 started with Q23 shorted

So, I replaced all the 2sc1318's and the caps associated with them 100p and 15p... Never found anything that measured bad, but the 15p caps looked like they might have gotten hot... Anyway, no more fuse blowing and listened to FM radio all day yesterday....Think I got lucky....
I did measure DC mV voltage on the speaker terminals prior to hooking up speakers...one was +2 or 3 the other - 10 or 12.... Is that anything to be concerned about? If so what would I have to adjust...or is this a "matched pair" transistor thing?

J

 

[Oldsansui441]

Nice work, glad to hear you have it up and running. If those dc offset measurements are in mV then those reading are really good. I don't think the 434 has adjustment for dc offset so yes it would come down to the matching of the differential input pair on the main amp. You are in good shape in regards to this though.

I wonder if sevarre (the OP) is far behind you with getting his 434 working?

 

[jagrunst]

Yes, I was wondering if Sevarre had any success also... I believe he started with the same output transistor shorted, so thought maybe my findings might give him a path to follow.... I was ready to throw in the towel, now I'm glad I kept at it.... Thanks for the support and guidance Oldsansui... I think I'll have to try another one now...seems the circuitry on stereo receivers is pretty similar....but I certainly don't want to get too overconfident. All the best!

 

[Oldsansui441]

Yes, I was wondering if Sevarre had any success also... I believe he started with the same output transistor shorted, so thought maybe my findings might give him a path to follow.... I was ready to throw in the towel, now I'm glad I kept at it.

I'm sure your findings can only help sevarre with his unit. Bet you are glad you kept at it, it can be time consuming but there is reward when you bring a non functioning piece back to life as you did.

Thanks for the support and guidance Oldsansui... I think I'll have to try another one now...seems the circuitry on stereo receivers is pretty similar....but I certainly don't want to get too overconfident. All the best!

Thank you, your welcome. Yes you should have a go at another, im sure you will be fine. That whole line of Pioneer x3x receivers are really nice. All the best to you also .

 

[sevarre]

jagrunst, that is awesome news! congrats! I had mine working for a bit a few days ago and I felt the same way about wanting to take on another one, haha. I've since started having some more issues with mine again, though.

Summary of what I've done so far:

1. Replaced every electrolytic cap on the power board and the amp board.*
2. Replaced every transistor on the power board and amp board (besides Q5 and Q6).
3. Checked resistor values for power board and amp board and they tested within tolerance.
4. Replaced diodes on power board. Did not replace diodes on amp board.
*did not change big filter caps

Summary of my results:

1. Powered it up and everything seemed nice! Nothing weird.
2. Played some music from computer to AUX input on the 434. Sounded great. Played at least an hours worth.
3. Went to play some stuff from the good ol' turntable... I had this sneaking uneasiness that something would go wrong.
4. Switched to PHONO input, started turntable* and got nothing
5. Tried playing from AUX source again. Nothing.
6. Tried listening through headphones from AUX source. Again nothing.
**made sure the turntable's pre amp was turned OFF.

Summary of what I've done since:

1. Checked all fuses. No popped fuses! So, I start thinking output transistors again...
2. Output transistors are all good!

At that point I was wanting to just hook it all back up again and see if I actually didn't get any sound before! Haha.

Because it seemed like stuff went south upon selecting PHONO input, maybe something could be going awry with the preamp/RIAA eq part of the amp board? So, that would be the Q1-Q4 area, correct?

I put the outputs back in and decided to measure some power board voltages (probably should have measured voltages on pre-amp part of amp board now that I think of it). I've attached my readings as images so they are easier to read. They don't seem that off, but maybe enough to create an issue? Collector current on Q1 and Q3 are a solid 3-4 volts under what the schematic indicates. Pins 4 and 5 are a solid 2 volts under the schematic, as well.

At any rate, just wanted to update y'all on what I've been doing on the project. I will keep measuring voltages and tinkering around to see if I can find anything amiss. Thanks for all the help getting me this far!

afterthought: could maybe be dirty controls? I gave the whole thing a thorough Deoxit treatment back in August, but maybe another one is due? OR, maybe something is happening in the MIC area of the unit? I see that the PHONO input goes through the MIC area while the AUX in does not...I will investigate.

 

[jagrunst]

Savarre: Nice to hear from you again...

I know the feeling---- Now where do I go?.....

Initially I replaced Q1-Q4 while working on that circuit board---didn't find anything that didn't pass testing.... after mine quit, I ended up changing Q15, Q16, Q17, Q18---they all tested fine, but replaced them anyway...I also repalced C39, C40,C45, C46, C47, C48, C50. --- none of them tested bad either, but something with changing them must have fixed it.... a few of the ceramic caps "looked" like they had gotten hot--- wish I would have found a bad component, but didn't....One of those components must have been intermittent / flaky.....

I've never hooked a computer up to a receiver to stream music...but was asking some of the younger folks at work how that worked...my son warned me about that and said you could blow things up...something about
"line"---- he said something about needing a special adaptor to bring the input to "line"---and plug into the "mic" port--- It had to do with running already amplified "stuff" into an amplifier..... Maybe someone can speak to this, because I really didn't understand..... At some point I would like to try "streaming" from a phone or computer too.

J

 

[sevarre]

Good to hear from you again, as well! Yeah, maybe I should be checking more of the ceramic/mylar caps... I will measure some more voltages. At this point I kinda want to just buy every component on AWK-034 and wire them all up on a breadboard according to the schematic, haha.

my son warned me about that and said you could blow things up...something about
"line"---- he said something about needing a special adaptor to bring the input to "line"---and plug into the "mic" port--- It had to do with running already amplified "stuff" into an amplifier.....

I have a "line out" output from my computer, so it should be safe to plug it in to the AUX input on the 434. It sounded pretty good, at least! I don't know a whole lot about the different "levels" for this stuff, but your son brings up a good point about making sure the output signal is at the correct "level" that the input device is expecting.

The AUX input on the 434 bypasses the preamp/RIAA eq section of AWK-034, so I think sending a "line out" to the AUX input should be relatively safe?

EDIT: Actually, talking about the different input/output requirements for this stuff got me reading this interesting sticky: http://audiokarma.org/forums/index.php?threads/amplifier-sensitivity-decibels-and-you.58829/

I measured my macbook pro's output voltage to be around 669 mV (at max signal strength with a 1kHz sine wave) while the AUX input sensitivity for the 434 is 150 mV. So, I think it should be fine as long as I don't turn up the volume too much (which I don't).

 

[jagrunst]

Well, I hadn't hooked up a turntable to my 434 yet and did that Friday night... Only played through one channel...Double checked everything and still didn't work... FM worked fine... Opened her back up and found the "MIC" jack is all busted up..the plastic housing is cracked...I presume some of the internals are contacting each other and shorting things out----found a replacement on ebay---hopefully nothing else was damaged---it will be a couple weeks before I can tinker with it again...Always something...

 

[sevarre]

Alright, so I think this is finally done!

Over a year later and I am almost there. After many mistakes, horrible soldering joints, and magic smoke, I was able to play vinyl through the PHONO input and my phone through the AUX input. I listened to the music via headphones, so haven't hooked speakers up to it yet (getting more and more conservative about things as this project has progressed), but headphones sounded good. Just a fun note: I managed to short the output transistors TWICE while checking voltages, ahah, so I won't ever be doing THAT again!

Some wire wrapped connections were getting pretty beat up, so I removed the wire wraps and have some of them connected via alligator clips at the moment. Any recommendations for best practices on redoing the wiring for this? Wire wrapping sounds like it's the best option, but is also sounds like it takes some skill. I also don't have any wire right now. Any recommendations for appropriate wire? Most of the stuff in there says AWG 22, so I think just getting some of that should be sufficient.

Sincere thanks to all for your help along the way. The knowledge this forum contains is amazing.

jagrunst: Hoping things worked out for you once you replaced that MIC jack!

 

[jagrunst]

Cool...glad to hear you kept at it... Mine has been performing perfectly....I'm considering another 434 as it/they sound better than the sx450 and sx636 that i've been playing with....Joe

 

[Oldsansui441]

Some wire wrapped connections were getting pretty beat up, so I removed the wire wraps and have some of them connected via alligator clips at the moment. Any recommendations for best practices on redoing the wiring for this? Wire wrapping sounds like it's the best option, but is also sounds like it takes some skill. I also don't have any wire right now. Any recommendations for appropriate wire? Most of the stuff in there says AWG 22, so I think just getting some of that should be sufficient.

Good to hear you have her up and running. Remove the remaining wire wrap off the posts as you have done on some already then remove about 3-4mm of the insulation on the remaining good wire, wrap once around post and solder. You should have enough length in wiring left to do this.

 

[sevarre]

Oldsansui, thanks for the tip. I did exactly that and it's working perfectly. Had to replace one of the ground wires and one of the chassis ground screws.

Also had to replace the treble pot. I think something was physically wrong with it because you could just spin it all the way around without stopping. Tried taking it apart to see if I could find anyway to fix it, but couldn't figure it out. LUCKILY, I found the exact potentiometer from a 434 on eBay, so I plopped it in and it works beautifully!

 

[Oldsansui441]

I found the exact potentiometer from a 434 on eBay

Nice work, good to hear you saved her.