Pioneer SX636 Rebuild

[Soundork]

Hello,

Before I start, I would like to thank Mark the Fixer for saving me enormous amount of time by creating a BOM.

I am posting, because I need help/guidance through the process of rebuilding a recently purchased SX636. I am going to use this post as a little intro as well, but if you arent interested in reading it, feel free to skip down to the questions section...

I bought the receiver from the local Craigslist. During the email exchanges, the condition of it changed several times...Upon first power up, it took about ten seconds for the sound to come up, then about a minute later a really loud static appeared on the right channel. I turned off immediately, but later that day powered it for a second time and did not hear music, only the loud static. Same after cleaning the controls.

Keep in mind that I am using this as a learning experience, this is also why I am asking so many questions. I have studied the diagrams (to the best of my abilities) and also gone through most if not all posts on the subject.

HERE IS THE INTERESTING SECTION:

I have attached a new BOM that needs vetting. My starting point was Mark the Fixer's BOM and the official one in the repository. Some of the parts on the list are obsolete now and I have proposed new alternatives. Also, in the process I discovered that Nichicon now makes "audio grade" capacitors (I haven't grasped that concept yet, but I am learning). For completion, I also pulled out these numbers even in places where I didnt think they are necessary.

Questions

Equalizer Amp Assembly (AWF-014-0)

1. Why is it ok to switch from electrolytic to a film capacitor for C1/2?
2. C5 and 6 look like power supply filtering capacitors, why not increase their value to 220uF?
3. Confirm that C11/12 do not have to be audio grade capacitors.
4. C13/14 Confirm statement that they don’t have to be electrolytic capacitors

AF Amp Assembly (AWK-035-0)

1. What are the benefits of going non-electrolytic on the coupling input and output of the amplifier i.e. C5/6 and C25/26?
2. C9/10 and 31, confirm benefits of increasing values to 220uf (especially the latter)?
3. C27/28 and 31 Confirm that these don’t have to be audio grade

Power Amp Assembly (AWH-034-0)

1. C1/2 Why film chosen instead of audio grade?
2. Confirm that C7/8 aren’t audio grade.
3. Confirm that should be audio grade capacitors.

Power Supply Assembly (AWR-060-0)

1. I think we get benefits from increasing the values of C6/7/11/14 and possibly C8/13?

Tuner Board (AWE-046-0)

1. C21: Why was a film capacitor used as opposed of an electrolytic like in the AF Amplifier for example?
2. C36: Why was not an electrolytic capacitor used?
3. C48/59/60 Why was this particular type chosen as opposed to the one chosen for the Power Amplifier?
4. C50: Why was not an electrolytic capacitor used? The AF Amplifier used electrolytic.


General Questions:

1. Is it ok to put 0.01uF across all power filtering capacitors to better insulate from the 60Hz hum?
2. Why was the UPW series capacitors chosen for replacement?

3. Mark the Fixer once said in a post that the tuner board should not be removed and I was wondering why.
4. I did go through the switches and potentiometers with the Radio Shack's fluid (which contains DeOxit) and in the process I was unable to remove the speakers A B switches as the screw started to strip. How do I proceed without completely stripping the screw?
5. I also found out the FM Stereo Indicator lamp neatly taped to the chassis. Any ideas why that might be?

Thank you for reading this.

Best

Boris

 

[Soundork]

Pron

Here is some pron for your pleasure.

This is my starting point. Besides the performance issues, it is missing the cap on the power button and for some reason the stereo indicator lamp is taped to the chassis. I dont know what to make out of that yet.

I also have question about how to clean up the baked and caked dust on the chassis. You can see it best on picture number two, to the right of the tuning capacitor on the FM board. I tried brushing it off with a toothbrush, but it didnt budge.

What is the name of the tool used to wrap the wire ends around the PCB posts?

The first two pictures are the ones that I took last, after cleaning the potentiometers and switches. I am really excited about bringing the receiver back to life and cant wait to post a picture with the blue lights glowing...btw I already ordered a whole set from Dave whom I highly recommend as he was very knowledgeable and his service was superfast.

Best

Boris

 

[Soundork]

List

So, do we agree that my list is the new official list?

I have confidence in it. Too bad my questions didnt get answered.

I would also like to get the non-capacitor related question possibly answered. For example, the question of how to clean up the chassis. Pretty sure that this smart bunch here has ideas.

Thanks in advance.

Best

Boris

 

[Awesomeaudio]

Hello There and welcome to the forum.
You have certainly come to the right place. Although I can't help you with this project specifically, there are those here who can.
Just be patient and help will arrive.

This unit should be quite easy to do as the layout is nice and open.

Get your parts list vetted and away you go.
All the best. :thmbsp:

 

[rcs16]

lots of ?'s
if you can fit a film/foil cap in the same area as an ecap then go for the film because it is more reliable and has better electrical properties such as leakage, dissipation factor etc.
i would have to go through the whole bom but the bottom line is,
use nichicon ukl or film for signal path
i select for 105C and 20% in ukl series as they are pennies more than 85C rated parts
you can step up to the next capacity size for an ecap used for supply filtering, usually as an improvement, unless the ecap is used for a specific purpose such as a timing or signal filter applications.

 

[zebulon1]

Sound at first with static?
Then no sound?

It's best to fix then restore.

Were you using the tuner? Did you try any other inputs? CD-aux, tape deck or turntable? If so try the other inputs.
First stage of the AF Amp has the 2SA726's. Known for giving crappy service.

Power supply voltage reading's?

 

[Soundork]

Hello There and welcome to the forum.
You have certainly come to the right place. Although I can't help you with this project specifically, there are those here who can.
Just be patient and help will arrive.

This unit should be quite easy to do as the layout is nice and open.

Get your parts list vetted and away you go.
All the best. :thmbsp:

Thank you for the warm welcome.

I think this project will turn all right. I see that after your message, help is on its way.

Best

Boris

 

[Soundork]

lots of ?'s
if you can fit a film/foil cap in the same area as an ecap then go for the film because it is more reliable and has better electrical properties such as leakage, dissipation factor etc.
i would have to go through the whole bom but the bottom line is,
use nichicon ukl or film for signal path
i select for 105C and 20% in ukl series as they are pennies more than 85C rated parts
you can step up to the next capacity size for an ecap used for supply filtering, usually as an improvement, unless the ecap is used for a specific purpose such as a timing or signal filter applications.

Thanks for the explanation.

I did not know how the power supply was sized and was unsure by how much I can increase the capacitance of the filtering caps. Also, I was not sure if I have correctly identified those on the boards.

Thanks for the capacitor temperature tip. I honestly did not consider that parameter as an issue, since the case seemed to be well vented.

Best

Boris

 

[Soundork]

Sound at first with static?
Then no sound?

It's best to fix then restore.

Were you using the tuner? Did you try any other inputs? CD-aux, tape deck or turntable? If so try the other inputs.
First stage of the AF Amp has the 2SA726's. Known for giving crappy service.

Power supply voltage reading's?

Thank you for your response. You do have a very good point...After doing an extensive research, my thought was to address the known issues that would cause this behavior, but I guess I should try to identify the offending component first...

I was using the tuner when all this happened. Originally, I was told that it takes about ten minutes until "some slight sound deterioration appears"...then the story changed to worse. I really didn't care. With the exception of the power button cap missing, it looked almost perfect. That was well worth the $20 I paid for it and I also knew that I could fix it (with some help).

The receiver did work for about thirty seconds for me. The sound was not exactly premium, more like a cheap AM/FM transistor radio from the 80's. Then the loud static noise started from the right channel. The noise was not affected by fiddling with the volume button, or switching to another sound source (even though I didnt have anything hooked up). At some point the FM signal completely disappeared. I then turned off the receiver.

The second time when I powered it up was couple of days later, after I cleaned the switches and potentiometers. There wasnt any signal coming from the tuner, just the loud static noise. It also faintly started to smell like hot components, the way they start to smell, when melting, right before starting to smoke...

I dont think I had it powered up for more than a minute, before turning it off. My first guess was the transistors on the power amplifier board, but I didnt pursue investigation.

I dont have the 8 Ohm/20W resistors that I was going to order along with the other components yet, but here is an idea...Let me know how crazy it sounds:

What if I got an 8 Ohm resistor and connected it to the speaker terminals and then dipped it in a glass of water?

Best

Boris

 

[zebulon1]

Just hook it up to a different source.
It has fuses to protect the speakers. Static is ok. That means the amps are probably working.

 

[Soundork]

Just checking in. Hoping to hear that my BOM is OK.

Thanks

Boris

 

[markthefixer]

List looks good, familiar . Congratulations

No time to do a deep comparison between your and my lists:
http://www.audiokarma.org/forums/showpost.php?p=6747895&postcount=6
looks similar with the inclusion of the tuner caps - which I generally as a rule of thumb, don't advocate fooling with. If you HAVE to, THIS tuner has just one adjustment, the stereo decoder PLL, and it can be talked through...

 

[audiojones]

Check C12 on AWR-060 power supply board. Is yours 220uf or 10uf? There may be a mistake in the schematic stating that it is 220uf when they actually put a 10uf in that spot.

 

[Soundork]

A little teaser from last night immediately after I turned the soldering station off. Note the super modern string technology utilized in the process...

I finally got to this project. Luckily, there were absolutely no hiccups, due to being organized 110% of the time.

It is all back together tonight, but unfortunately the lamp on the dial pointer is not working. I also need to adjust the power amp, but cant do it at the moment, because in my infinite wisdom, I somehow omitted the 8Ohm resistor needed for alignment from my latest version of the BOM.

Soooooo....I am hoping the nearest Radio Shack has an 8Ohm resistor and I can declare a victory tomorrow (I did purchase a whole set of lights, so I do have the light for the pointer at hand).

I will post a picture once its all lit up and glowing...

Best

Boris

P.S. I no longer see the option to upload my BOM, but feel free to contact me if you need it.

 

[audiojones]

You don't need the 8 ohm resistor across the speaker terminals to adjust the amp, just make sure the volume is turned completely down and select a dead input source like aux with nothing connected to it.

 

[Soundork]

This is it, folks. Thank you for your support throughout this project. I got some pron for ya....:

First, we have it against the component it replaces

Here is some more:

All I need now in order to complete the restoration is to find a cap for the power button and a socket for the phones, because the old one was in pieces.

Once again thanks to everyone.

Best

Boris