New sx-636 Refurb Issues and Questions

[fromnowon]

Hi again, I'd really appreciate any comments.

I'm still trying to find my problem with AWK-035 - fresh start! Problem is still no Left channel.

1) This is my signal at 21 and 23, inputs to AWK-035, sending signal through AUX left mono in to split it down both sides:


2. Here is what Pins 10 and 11 look like, 10 on top, confirming that signal is not getting to L channel out on this board:


That definitely confirms the signal is not being passed from pin 21 to pin 10.

3. next I decided to check at R13 and R14, which feed the base of Q1 and Q2, respectively, after several switches and the volume control.
Here's what I get there, looks good I think:


4. I did some reading, and I think this is a "common emitter" amplifier topology. So the output I should check at Q1 and Q2 will be from the Collector, which passes the signal to subsequent stages.
Here's what I get from the Q1 and Q2 Collectors:

The signal for Q1 completely disappears.

5. I pulled Q1 (which is a 512-KSA992FBU) and is seems to test fine, hFe 398, uf 673mV, PNP, on my tester.

6. I cleaned up the pads with solder wick and they look like this:


I haven't soldered in a new 512-KSA992FBU replacement yet, but I wonder if I should do something differently this time.

 

[fromnowon]

oh, I also checked voltages on all 6 transistors, here they are:

 

[fromnowon]

one more, here's the whole neighborhood around Q1 from top:

 

[pa_200]

Can you check the signal and voltage on both legs of c5 and c6 and post the results.

And can you recheck this strang looking soldering?

 

[fromnowon]

thanks! - sure,

C5 and C6 being 1uF WIMAs, they were flush - so I replaced them and left the leads longer so I could test . . .

I put in a new A992 . . .

Reflowed that "strange" solder . . . .

Just for fun plugged in headphones, NOW BOTH CHANNELS WORK and it sounds very nice too.

(but I don't know which of all that fixed it)

 

[fromnowon]

Thank you pa_200

 

[fromnowon]

I'm betting it was the solder pad you circled.
Here's the strange solder, which was Q3 base / 1 leg of c11, in yellow below.
Maybe that was shorting out the Q1 Collector's signal?
(When I got this receiver it had a blown left channel fuse.)




after I fixed it:

 

[pa_200]

One basic question about the transistors on the AWK-035. Did you replace all of them or which one was replaced by you, or did you leave all of them alone?

If you take the picture with that bad soldering and you can zoom in on the two marked pins, it would be great if you post a magnified picture of the old solder position. From my point looking on the position, the right pin is the base of q3 and it looks like the solder around that leg has no contact or a very loose contact to the pin.
I always use a magnifying glass and recheck every soldering on each board before and after finishing work on that part.
It wouldn’t surprise me if it was still the old transistor installed since the solder points of the emitter and collector leg seem to be original on the first picture.

So a final question to the 6 transistors q1 – q6. Have you changed all, or which one are installed now?

Edit:
I just had a second look on all your pictures of the foil side. If it was my unit, I would use my magnifying glass, thoroughly check every soldering and reflow every suspicious / unprofessional looking solder point!

 

[fromnowon]

Thanks! Yes I replaced all six transistors on AWK-035, even in the "before" picture, with L channel not working, they were replaced.

Here is a zoomed in "before" picture, as you had circled (with a new 512-KSC1845FTA replacing the original 2sc1344, so unfortunately I have to confess that must be my soldering) when left channel did not work:


Here is the same view after I reflowed that pad with the emitter of Q3 on it, after which the left channel did work:


You make a great point about checking all the pads - I will go over it carefully once more, maybe take it out in the sunlight. This board was a challenge as I had numerous lifting pads and there are some areas with many components in a small spots. I'd do better if I removed the board altogether . . . but I decided not to do that. I attempted to do the work with the receiver vertical and the board freed up and hanging on its wires, so I could swing it back and forth. Just not the best working arrangement and difficult to get good light in there too.

Well, I listened last night for a few hours and it sounds really nice! Very powerful, nice and clear, strong bass. However I do get a very minor amount of background hiss which could be the source, I'm not sure yet. I still have that Phono EQ board to recap, and the two large caps to replace. Also, I need to do the adjustments on AWH-034 which on first pass didn't work out very well, have to try again. There is also still a minor amount of static in the volume pot, even after all the cleaning, just a touch . . . I could live with it, but it makes me wonder if anyone ever tries to replace the volume pots with perhaps an Alps . . . I see that it has tabs for Loudness on it - interesting.

I can't tell you how much I appreciate the help, and it's been a great learning experience for me. Still more work to do on it!

 

[pa_200]

Are you using solder flux? I use it always, even if there is some flux inside the lead.
I'm not an expert at all, rather a newbie who has worked on 5 pioneer in the last 12 month. So I had to learn and make my experience with these beautiful receivers as well.

One very good thing is while working on a pioneer, there is no need to disconnect all the leads, just take them out of the white holders and careful loosen all those twisted cables, so you get enough space to lift the boards so one can work on both sides.

I give you a link to one of my post where I wrote down some of my points, to help other newbies as well.

https://audiokarma.org/forums/index...sx-737-phono-only.884661/page-4#post-13118661

I plan to write a longer summary about my experience to help all the “non-experts”, since I am so grateful for the help I have got here at AK.

 

[fromnowon]

Hmm, no I have not been using using flux, other than what is in the solder already.
I do have some . . .
On the next board I'll try putting some flux on a tooth pick and dabbing a little on the pad and lead of whatever I'm about to solder.
(I have been using flux with solder wick and it sure helps the wick soak up solder.)

Thanks for the link. You make a great point about pictures and the tools we have today. I can see things in pictures that I take with my phone that I can't see with my eyes, or even as well with a magnifying glass. I'm sure I looked at that bad joint and just missed it as in real life it's so small! But in the picture, wow, it looks like there is gap around the transistor lead. (in reality that gap is probably less than 1mm)

These Pioneers really are beautiful. The one I'm working was sold in a flea market for $20 not working. At the moment, it sounds GREAT.

 

[pa_200]

I use a Q-tip or something similar from my wife's "make-up workbench" to dispense the flux to the pad.

As well we shouldn't forget, that the majority of the vintage owner, had their youth around 1975 to 1985. So we are all have the “privilege to us glasses” if we want the Eagle Eyes like 40 years ago.
So we have to use all available means to be successful.

 

[fromnowon]

ha ha, that's true!

Also, on those solder pads, I've been trying to be "quick" to not damage anything with heat. Maybe another second or two wouldn't hurt so the solder flows better.

 

[pa_200]

I use around 320-350°Celsius on my solder iron, a flat tip around 2 mm, clean the tip always before and when the solder flows, one to two seconds is the maximum time you need on the pads. And two seconds can become a really long time!
https://www.ebay.de/itm/Lotspitzen-...079782?hash=item2ab0196166:g:NOcAAOSwSI5bWHOY
Something like this is very helpful for cleaning the tip and I guess you have it at home. "Dish Drops Scrub Buds"
https://www.ebay.de/itm/1x-AMWAY-Ho...a=1&pg=2334524&_trksid=p2334524.c100667.m2042

 

[merlynski]

ha ha, that's true!

Also, on those solder pads, I've been trying to be "quick" to not damage anything with heat. Maybe another second or two wouldn't hurt so the solder flows better.

Lifting pads is caused by too much heat and pushing too hard with the tip of the iron. When I solder and unsolder I use a very light touch, add extra solder, and extra flux if needed. If your iron is properly hot the solder will liquefy and flow without pressing hard, let the heat do the work. Extra solder on the tip makes liquid solder flow onto the joint so you don't need pressure. Once it flows properly remove the iron and let it cool. Extra flux on the solder-wick helps transfer heat as well, so little pressure is needed. I (almost) never lift a pad unless somebody before me has damaged it.

 

[markthefixer]

The extra flux cleans your TIP - and then gets good heat flow IF the tip hasn't been cooled too badly by the flux.
When desoldering it is even MORE critical that the tip is FRESHLY cleaned (seconds, not minutes). Wetting the desolder tip with fresh solder does help too.

The tip really shouldn't touch the foil at all - using PRESSURE to get the solder to melt is the BADDEST JUJU for the foil.

Clean and wet the tip and let the wet solder transfer the heat.

I have professionally desoldered some REALLY dicey stuff in my career. Successfully. Without damage. Repeatedly.

 

[fromnowon]

Thanks for the tips and comments, really appreciated

BTW,

The only issue is some faint, random/sporadic fuzzy static in between songs, or when I turn down the volume all the way (I'm using AUX). It comes and goes, very quiet. I hope replacing caps / transistors on the tone amp and eq amp boards will get it. I've also not cleaned the pots and controls and switches yet so maybe that's the cause.

- I think it was picking up interference from my cell phone

 

[Oldsansui441]

I think it was picking up interference from my cell phone

Yep, that will do it.

 

[fromnowon]

Now that the tone board is sorted out, I've been listening to it a lot, for extended times - it sounds really good. Mainly I'm using Loudness "in" and tone controls centered. It has a very solid low-end, and a really clear, clean top end sound. It's really addictive.

I'm looking forward to seeing if these filter caps make a noticeable difference in any way (they were suggested by Avionic in a different SX-636 thread because they fit the clamps, and I decided to spring for them for this project). I think they are very cool-looking, even beautiful:


I'll solder on the ring terminals.

If I power it down with music playing, with the original filter caps in, as the caps discharge I get some weird distortion and even some squealing sounds in my headphones. It'll be interesting to see if the new caps make a difference in how long it takes for the sound to fade that way. I love the bass as it is! I'm not sure what to expect the effect of the new ones to be. They are 6800 uF, same as originals.

There is some slight background hiss in between songs, or with volume at 0 . . . not that objectionable, maybe the new caps will help with that.

We'll see!

 

[pa_200]

Do the caps come with the ring mounting or did you attach it? Can you post the order number for these caps?
Just one advice before you start working on the big filter caps, because it happened do me already.
1. Make absolutely sure that both caps are completely discharged. They can still hold a lot energy and create nice sparks across your unit!
2. Make a few pictures where you can clearly see all the leads going to both caps AND an extra drawing where you mark the PLUS and MINUS pins on the caps, together with all the connections where the leads come from.
3. For the first power up with the new caps, USE the DBT for your own protection!! There is a 50:50 chance that you screw it up.
In my case, I made only two picture from the first SX-737 because I thought I have everything on picture and can remember the wiring, but I didn’t. But I started with the DBT and had a constant very bright light on the first attempt. Lucky for my, that my second SX-737 was still original, so it helped me, to trace all leads and correct my self-build-in mistake.