Pioneer SX-737 rebuild BOM

[loweran]

Here is the board. I'll go back through and double check.

 

[loweran]

Oh. I just saw what I think is Q4 in backwards when I posted the pic. I'll check.

 

[loweran]

Thanks tsd71. That was it. I had Q4 backwards. Got it re-oriented, all the voltages are good! One more board down and it is functioning well! Next up is the protection board.

 

[Penn42]

Thanks tsd71. That was it. I had Q4 backwards. Got it re-oriented, all the voltages are good! One more board down and it is functioning well! Next up is the protection board.

Couple newbie question time. I know they've probably been given back in this thread somewhere, but how do you know what the correct voltages are supposed to be? Like if I wanted to know for random receiver x. How do the folks in-the-know know? And also what do you use for a convenient grounding point when taking your readings? I know some of the pins are grounds themselves, but can you just use the chassis?

 

[Rico126]

I say on the previous page that you were trying to set voltages and they weren't moving. Just a heads up, and I'm sorry if it was mentioned before; the manual is wrong on the offset and bias pot adjustment. It has the pots reversed. Look on here for the post, search sx-737 bias. Markthefixer pointed this out.

 

[Rico126]

Couple newbie question time. I know they've probably been given back in this thread somewhere, but how do you know what the correct voltages are supposed to be? Like if I wanted to know for random receiver x. How do the folks in-the-know know? And also what do you use for a convenient grounding point when taking your readings? I know some of the pins are grounds themselves, but can you just use the chassis?

Generally the voltages are listed on the schematic next to components, and yes the chassis is a good source for ground.

 

[Penn42]

Generally the voltages are listed on the schematic next to components, and yes the chassis is a good source for ground.

Thanks!

 

[loweran]

Ditto on what Rico126 said. The service manuals have the voltages for the pins listed. They also have some board component voltages as well.

Just a heads up, and I'm sorry if it was mentioned before; the manual is wrong on the offset and bias pot adjustment.

Yep. I had that in my notes. It's pretty obvious though one you work on it and try and dial them in.

I can't believe I got that transistor in wrong. I was being so careful. I think the issue was that the larger one was BCE and this one was ECB so I installed them the same.

 

[loweran]

So far, I have noticed the bass is tighter or less muddy. I still need to do the protection board, the EQ and the phono. I think I will start with the protection circuit next.

 

[loweran]

Power protection board done. On a roll. Control board and phono to go. Less and less parts in the box! I noticed the relay clicks almost imediately. Did not expect that. I also noticed that the speakers thump when I power on and off. Is that normal?

But. Oh my gosh this thing sounds so good. Really. I mean it sounds fantastic through the Epi speakers.

 

[loweran]

Pics of he protection board.

 

[Penn42]

Power protection board done. On a roll. Control board and phono to go. Less and less parts in the box! I noticed the relay clicks almost imediately. Did not expect that. I also noticed that the speakers thump when I power on and off. Is that normal?

But. Oh my gosh this thing sounds so good. Really. I mean it sounds fantastic through the Epi speakers.

This is really cool! Been following this thread for a while and I'm glad it's all coming together. Giving me hope I'll be you soon when I start my 535.

 

[loweran]

So I just can't help but think something is off on the protect circuit. Is it normal for the relay to engage immediately when powering on? Also the speakers thump when powering on or off.

I checked the board component placement and they all seem to be installed correctly. I also checked the cap values against the BOM before installing. I will go back through and double check.

 

[loweran]

Looking at this a little further, seems Q7 is the relay driver transistor. Is C6 the timing cap? I need to double check the values.

 

[loweran]

Another note. The filter caps seem to hold a charge over night. I have to discharge them every time I work on the receiver.

 

[glen65]

How about that. The only thing that burned is something that grows back like new. sorry for your pain, but at least you will repair that whereas a burned chunk of wire insulation might live on in that unit.

Is that board clean? It looks like it is a bit dirty, needing a nice wash. Not getting into how to do stuff, we have Glen handling that job in this thread.

I haven't staked any claim of ownership to the thread. If others wish to add something, fine.

 

[glen65]

Another note. The filter caps seem to hold a charge over night. I have to discharge them every time I work on the receiver.

That's normal

 

[glen65]

Also, thank you Glen for the help getting me to this point. Also thanks for the de-solder tool. It made this a lot easier. I got a new tip for it per your advise and it worked great. Pioneer pushed the leads all the way down against the pads so I had to apply heat with the solder iron and pry then up while hot. Worked well though. I did not break any pads.

Any idea on what to check to get the DC offset sorted?

There are times you might have to actually add solder first before de-soldering. If you run into a component which you think will need too much time spent on it,
you can try cutting the component flush at the board and pull whats left of the leads through the foil side.

 

[glen65]

Yes it is dirty and the foil side has a lot of flux on it from the factory I suppose. I have not cleaned it all up yet, though I did clean where I replaced the components. I bought some acetone per Glen's instruction but I have been using 99% alcohol to this point.

Looks like you're going to need to hit the foil side with acetone to remove all of that flux residue. Just keep it away from the components themselves.
Acetone is rough on plastic and can remove the conformal coating on the carbon film resistors.

 

[loweran]

Hey Glen! Welcome back!

That's normal

I figured so. I did read accounts that they discharge on their own. I also noticed that when I discharge them, they trickle back up after I remove the resistor. I assume that they are pulling from other caps on the boards, but I don't really know how they work.

There are times you might have to actually add solder first before de-soldering. If you run into a component which you think will need too much time spent on it,
you can try cutting the component flush at the board and pull whats left of the leads through the foil side.

I figured out that adding solder helps. I also have to clean and tin the tip like a soldering iron. Smaller components work better than larger ones. I have been using wick in cases where the solder is under the lead and holding it to the pad. Getting better at it.

Looks like you're going to need to hit the foil side with acetone to remove all of that flux residue. Just keep it away from the components themselves.
Acetone is rough on plastic and can remove the conformal coating on the carbon film resistors.

I went over the board with acetone. I did not know that it could harm the resistors, so I hope I didn't do damage. All the voltages are in line, at least for now. That one was really dirty for some reason. The power supply and protection board were cleaner. I used alcohol on them and my kem wipes.