• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Pioneer sx-636...could use some help

736510264_photobucket_51712_.jpg

736510264_photobucket_51713_.jpg


Took me longer than expected to get the funds and order components, but finally got them and got a little work done. So far have done work on the AWH-034-0 amp board only, new caps and upgraded transistors as suggested by mark. I haven't actually done the mains(Q11-14) just the caps and transistors on the board itself. Did an ok job I suppose, im guessing it could look nicer but for me first try i'm happy...also it did not start on fire when powering up so I guess that is a good indicator :D

Very happy so far with the results, cold start and the issue mentioned previously with distortion/crackling from the amp section is gone. Powers up without a peep now and the music is sounding better already...although that could be in my head. :scratch2: I'll keep at it and track my progress hopefully things will go a little faster now.
 
Also...quick question, How far down would you guys recommend putting the components in? Is it just a matter of tidyness or is it better to have caps touching the pcb? The originals were right on it.
 
Thank you for the thorough and very detailed posts. I have had my 636 at the repair shop since Nov. 2010, and I am going to recover it from them and fix the darn thing myself. Mine has the exact same problem as yours, plus a few indicator lamps.

Good luck!
 
randallflag said:
Also...quick question, How far down would you guys recommend putting the components in? Is it just a matter of tidyness or is it better to have caps touching the pcb? The originals were right on it.
Click to expand...

When placing components on a PCB, you just use good sense:

Not so high as to hit another part or be able to bend over on its own. Or twist in a way that can short out its own leads.

Not so low that you can't go back and remove the component and reinstall if necessary.

For me, small can transistors I have about as much legs as the body is tall. Tall body transistors, about 1/2 as long legs as the body. Looks like you got 'em just right.
 
made in china said:
Thank you for the thorough and very detailed posts. I have had my 636 at the repair shop since Nov. 2010, and I am going to recover it from them and fix the darn thing myself. Mine has the exact same problem as yours, plus a few indicator lamps.

Good luck!
Click to expand...

Well each unit should be dealt with on a case by case basis, for me I'm feeling that the aluminum 1451's and the tiny blue sanyo caps were probably the problem...but considering I replaced all the transistors I can't really know for sure. Just those components is pretty cheap, the only purchases that hurt my wallet is Q11-14 as they were $4 something per.
 
I see you removed everything at the same time and then went in an installed all the new parts. I was advised to remove one at a time and replace it with the new part before moving on to the next part.
 
qprhooligan said:
I see you removed everything at the same time and then went in an installed all the new parts. I was advised to remove one at a time and replace it with the new part before moving on to the next part.
Click to expand...

That's probably a VERY good idea considering if there was a problem I'd have no idea which component was a problem. Very good advice that I should adhear to in the future...i'm still learnin.
 
I guess I expected these transitors to have some sort of thermal compound behind them but the only thing I see is a plastic film of some sort, or the compound was clear in color. Do I need to put something on these or can I just slap them in?

photobucket-3310-1310869466338.jpg
 
They are more then likely it is made of Mica a rock sliced very thin. Be very careful when removing it to clean up the heat sink. Take a new razor blade and carefully try and ease up the insulator off the metal. You do not want to crack it at all , ideally a new one is used each time . Clean up the heat sink with rubbing alcohol and put the new paste onto heat sink and place the insulator down .
Check with a ohm meter (RX1) to see if there is a short from the top of the transistor to the heat sink when done.



Barney
 
Oerets said:
They are more then likely it is made of Mica a rock sliced very thin. Be very careful when removing it to clean up the heat sink. Take a new razor blade and carefully try and ease up the insulator off the metal. You do not want to crack it at all , ideally a new one is used each time . Clean up the heat sink with rubbing alcohol and put the new paste onto heat sink and place the insulator down .
Check with a ohm meter (RX1) to see if there is a short from the top of the transistor to the heat sink when done.



Barney
Click to expand...

Well that certainly makes more sense, thank you Barney. I will try to be very careful then as I don't have replacement mica washers. Just to be 100% on the same page....1. Paste goes on heatsink, 2. Mica washer goes on top of paste, 3. Transistor goes on top of washer. Is that correct or do you need paste on both sides of the washer?
 
randallflag said:
Well that certainly makes more sense, thank you Barney. I will try to be very careful then as I don't have replacement mica washers. Just to be 100% on the same page....1. Paste goes on heatsink, 2. Mica washer goes on top of paste, 3. Transistor goes on top of washer. Is that correct or do you need paste on both sides of the washer?
Click to expand...
:thmbsp:

The Mica is to fragile and breaks easy so would be hard to do the paste onto it. you do not need it on the other side. A little goes a long way on the application of the paste.
Clean up any excess after you get it placed with a "Q" tip.


Good luck.

Barney
 
You can still get them , but I have to mail order mine . Not offered local any more here.

I was just wishing you some luck, it is not that hard of a job.



Barney
 
Ideally the Heatsink compound should be on BOTH SIDES of the mica. Putting it only on one side is about the same as not using any. The purpose is to fill any and all microscopic gaps to allow and enhance heat transfer. Barney's correct in the amount used. Just enough to give a thin film. Any more than that and you actually decrease the efficiency of the compound/mica combination.

The original stuff used by PIONEER was clear, almost like a nail polish and it was used as an adhesive. Again, use a razor blade to get under the mica(either on the heatsink or transistor.) Make sure it doesn't split. Rice grain sized dollops on the transistor and the heatsink, then screw it together. You want it to be able to ooze just to the edge of the transistor. Practice will help. A little over outside is ok (mech. pencil lead diam). But 1/8" squeezed out is too much and you need to open it up and wipe some off evenly, or do it all over. It sounds like it's rocket science, but it's really not. If you've ever taken apart a PC's CPU from it's heatsink, you'll see what I mean by a thin film.

I've found the TO-3 mica's occasionally at Ratshack, but like Barney said, it's almost exclusively Mailorder now.

I paste the transistor, then place the mica on it, squeeze it down so it covers the transistor 80%. Then a drop more on the top side of the mica. Screw down and wipe off any excess from around the edge(should be less than a small grain of rice. Anymore than that, start over as there is too much inside.)

Larry
 
They're in!!! I was able to get the old washers off without breaking them. I took the previous advice and managed to get a razor underneath them. Some rubbing alcohol to loosen things up and peeled them off. Christ they are thin and brittle, kind of nerve-racking knowing I had nothing to replace them with. Then spent a little time cleaning them up very carefully and scraping off excess on the heatsink. I then put a few dollops of new thermal compound on the new transistors, using an xacto knife i then spred a very fine layer on the transistor itself and placed a washer on each one. Then a few on the heatsink itself and sandwiched them back in and screwed them down. Then checked for shorts from the casings to the heatsink. All fine. Only problem encountered was D5(varistor?) lead pulled out at some point and barely had enough left to re-solder. Powered on and let it play for awhile to heat up. Again no smoke or fire...:music: . Both channels fine.

So will I need to adjust those 100 ohm pots now? Manual recommends it if replacing any transistors on the amp board.
 
Yes, adjustment after work.

Also, didn't see it mentioned, heat sink compound should be NON-conductive, some are ("arctic silver") and we have seen some delayed (go figure.. :dunno:) ill effects when they finally short out.
 
You must log in or register to reply here.
Back
Top Bottom