Assessment/advice on a sx-727

[markthefixer]

Alright, got another board done, and was starting the am/fm board...however, I am having a complete dog of a time getting to the bottom to de-solder. I loosened the wires coming in from the left, and the board on the right, and was carefully pulling, trying to keep it neat at the bottom (where a large majority of the solder-stick plug things are).

Is there any way to get better acess than this, or any wires that could be carefully documented and de-soldered to more easily replace the caps? Seems like pioneer kinda jumbled up the order of the wires near the board as well, they all tend to go through one another, not making this any easier.

Sometimes a few key wires can be unsoldered. But the tuner board usually is a tight "fit". Usually end up standing unit on end, pivoting board out 45 degrees or so and squeezing in to do the leads.

Pioneer was refining their skills back then....

Things got better and better.

 

[33&athird]

:tears:Okay, i'm kicking myself here. Powered up, main cap blew. Seems like it may have been installed backwards, no-one to blame but myself...I should have recorded it better. Looking at the schematic its the one for the -36 volt line to the power amp. Looks like i'm going to order another one, and a 3A fuse. I just can't get over what a dumb mistake it was...And on top of that, I couldn't tell if the Deoxit repaired the channel problem. Jeez...I don't know why you would care but I had to write it out somewhere. On a different note, I think i'm going to have post tramtic stress disorder, I never want to see another cap explode, it's terrible

EDIT: worth mentioning, the black wire isn't necessarily the negative on the cap...or at least in this case:scratch2:

 

[larryderouin]

We ALL MAKE MISTAKES! It's called experience and part of the learning curve. Don't feel bad. It's happened to most of us at one time or another. The best outcome of this is 1.) You didn't get hurt, and 2)you learned that you need to double check everything before plugging in 3.) That the function of the wire doesn't necessarily match it's color.

First time you dumped your bicycle and tore the bark off your knee, you swore you'd never get back on a stupid bike. Next day, you got back on and learned what NOT to do to cause you to dump the bike. See?!?! Experience. You'll make an extra effort next time NOT to repeat the error.

Hopefully you used at least a Dim Bulb Tester.....or best case a Variac.

Good job so far. Keep it coming.

Larry

 

[33&athird]

We ALL MAKE MISTAKES! It's called experience and part of the learning curve. Don't feel bad. It's happened to most of us at one time or another. The best outcome of this is 1.) You didn't get hurt, and 2)you learned that you need to double check everything before plugging in 3.) That the function of the wire doesn't necessarily match it's color.

Yeah, it took a couple days, but i'm feeling better about it. I figure at least it was just a cap, and not anything else like output devices and the like. I should have definitely double-checked this one, I had been checking the other boards, and only had one cap flipped, but that was an easy fix. I was probably just too eager, as I was really wanting to see if the Deoxit stuff had brought back the channel or not. Looking at it today, the black wire is the ground, but if the cap is for a negative supply, that would be the positive side of the cap.

Hopefully you used at least a Dim Bulb Tester.....or best case a Variac.

heh...that would have been a great idea, and indeed, should have been done. I don't have a dim-bulb tester, because my uncle gave me a variac. However, that variac needs a new cord, and i've been putting it off...I think i'll do that very soon, and use it next time I attempt a startup.

Good job so far. Keep it coming.

Larry

Thanks for the words of encouragement...I have a bit of experiance with building something from scratch, but not going in an replacing...there is a learning curve, but I think this was a good start.

I'll have pictures up after I replace the cap...it looks pretty good, except for the main caps, for which I used PC boards to mount too, not stock looking in the least, but a necessary evil. On a positive note, some of the boards look alot less clustered with the smaller caps, I can imagine the power supply caps are much better off for it.

 

[markthefixer]

First you fix the variac, AND if the variac does NOT have an inline ammeter you go to http://www.allelectronics.com and order up one of these:

http://www.allelectronics.com/make-a-store/item/PMA-5A/5A-AC-PANEL-METER/-/1.html (5 amps AC)
or
http://www.allelectronics.com/make-a-store/item/PMA-1A/1-AMP-AC-PANEL-METER/-/1.html (1 amp AC)

depending upon the variac's power, and wire it inline. You will quickly get used to the power-up "curve" of voltage vs amperage vs time for a unit in trouble or a unit that is operating properly.

I made mine with a "switch cord" which is a molded plug with a female receptacle and male plug and a 2 wire cord going to a switch - I replaced the switch with the meter, and actually use the cardboard box the meter came in as the enclosure ( I cut a window). It goes between the variac plug and the unit under test, and with the long cord, I position the meter where I can easily SEE it, and the chassis at the same time.

 

[33&athird]

First you fix the variac, AND if the variac does NOT have an inline ammeter you go to http://www.allelectronics.com and order up one of these:

http://www.allelectronics.com/make-a-store/item/PMA-5A/5A-AC-PANEL-METER/-/1.html (5 amps AC)
or
http://www.allelectronics.com/make-a-store/item/PMA-1A/1-AMP-AC-PANEL-METER/-/1.html (1 amp AC)

depending upon the variac's power, and wire it inline. You will quickly get used to the power-up "curve" of voltage vs amperage vs time for a unit in trouble or a unit that is operating properly.

I made mine with a "switch cord" which is a molded plug with a female receptacle and male plug and a 2 wire cord going to a switch - I replaced the switch with the meter, and actually use the cardboard box the meter came in as the enclosure ( I cut a window). It goes between the variac plug and the unit under test, and with the long cord, I position the meter where I can easily SEE it, and the chassis at the same time.

That is a great idea, i'll try to order one later. Would it be better to have it on the AC input or AC output? I could make a small box with a built in plug for a easy project. To be honest, I never even thought to add one, and it would increase its functionality greatly...thanks for the thought and the links:yes:.

 

[markthefixer]

An IMPORTANT note:

This variac/ammeter combo does NOT provide the safety of a dim bulb tester for something that suddenly without warning goes kaflooie....

The dim bulb is always on line waiting, whereas the variac/ammeter combination depends upon you tuning DOWN the voltage.

I have a dim bulb setup as well, and use it as often as the meter and variac.
That's the beauty of the stacking inline plugs, I can reconfigure quickly and easily.

If you are going to make boxes for the meter or dim bulb, you could put a standard IEC power receptacle on one side and use a standard cord to bring power in, and a standard power plug on the other side for the load.

 

[33&athird]

Been a long time, but rather bring up this topic than make a new one;

For one, the replacment cap is in, unit powers on, stays on, no problems. However, a couple weird things;

1) the left channel seems weak compared to the right. However when the volume is increased to about the 2nd marking, both equal out quite well...no idea what could cause this. Maybe another light Deoxiting is in order?:scratch2:...don't really want to pull the board again, but if its a big deal, then I will. Just weird, more than anything.

2) the right selection control (source control) appears to be dropping the channels occasionally, I assume from bad connections, can deoxit be used on this part as well? maybe a soaked q-tip would be better than spraying it everywhere?

Other than that, everything seems fine...in fact, when everything is working as it should, it sounds fantastic. Without a antenna, it was pulling in some fm, and it was really great, the tuner is really well designed. I hope to try out the phono section once these newer issues are dealt with.

~On the variac note, still working on it...was going to make sure the thing worked before going into it. The old cord nearly welded the plugs to an outlet; mental note; never trust old power cords. Shouldn't have even tryed it, but it had worked before (around a year ago)...Wish I knew when it was made, i'm guessing the 40's or 50's...since the General radio comp. went out in the 70's...

 

[markthefixer]

Probably needs more deoxit and lots more twisting... Use rags to control deoxit overspray, don't touch rotary switch contacts - they bend and then you're screwed.

With clean pots, the most likely cause of channel imbalance that evens out with higher volume is a protection relay with old damaged contacts.

You can try temporarily bridging the contacts to see if that brings up the volume, but the best strategy on a unit that old is to just replace the relay. which is a bit of a job -

The old case type isn't really available, and there's a whole thread dedicated to it.

BUT I have found a relay that while it only has two sets of contacts instead of four (stereo only needs two sets), it is a SNAP-IN fit to the old case.

Of course you have to get the wires from the old relay core to the new relay core.

Usually I document the heck out of the wires , colors and connection points on the old relay, then cut the solder tabs with the wires attached off the old relay one at a time, make additional cuts in the tab to easily remove the rest of the tab with desoldering heat - the paramount consideration is to NOT HEAT DAMAGE the wire OR it's insulation. Once all are free, I install the new relay mechanically, then one at a time mount and solder each wire - it's EASIER that way to get the solder iron in without damaging any wires...


You could try opening the old relay and burnishing the contacts with mild abrasives but that only buys you weeks or months until it needs a do-over... and to get atr the contacts is almost as much work as replacing it.

This is the thread with pictures:
http://www.audiokarma.org/forums/showthread.php?t=150439

here's my info on the snap-in relay:
----------------------------------------------------------------------------------------
----------------------- ly2f-dc24 -------- top ears wide tabs --- ~ 1 1/4 standoff -----
----------------------------------------------------------------------------------------
---- DPDT ------------- omron ly2f-dc24 mouser part number 653-ly2f-dc24 ---------------
----------------------- dpdt 24v no suppressor or indicator ----------------------------
---- EARS ------------- ears on top of case --------------------------------------------
----------------------- solder tabs ----------------------------------------------------
----------------------------------------------------------------------------------------

 

[33&athird]

Alright, thanks for the information, I would never had figured the relay could be doing it...I assumed the one-click thing was pretty final, and it activated everything equally. I'll certainly read the topic and look into the relay. I don't know...it's not insanely loud when it evens out, I may consider just leaving it as is, but have the feeling it may get worse over time.

Here's another one I noticed; how can you get that thousand-dollar feel on the knobs again? what I mean is that my sx-525 (no work on ti at all, ever) has a nice even resistance on the volume and balance pot, but the sx-727 which the pots are working pretty well on, and have been cleaned feel not loose, but not very strong...kinda anemic. Is there anyway to restore the great feel, like the 525?.

I think the first thing is to fix the selector, it may be causing imbalance as much as anything...But at least its pretty simple, first turning it on, I was really watching it, making sure it started up correctly, and then only one channel was playing, I felt terrible, but finding out it was just the switch was great. Originally I thought I had blown something:sigh:. Judging by the brief test when everything was running well, all this is worth it...great sound, as well as looks.

 

[Rockmore]

what I mean is that my sx-525 (no work on ti at all, ever) has a nice even resistance on the volume and balance pot, but the sx-727 which the pots are working pretty well on, and have been cleaned feel not loose, but not very strong...kinda anemic. Is there anyway to restore the great feel, like the 525?.

Thats' because the SX-525 is more of a classic than it's bigger brothers LOL- bigger isn't better...

...And... unless youre wanting to try and keep your 727 all stock, and/or actually try and find stock replacements, it's time to start thinking about what modern day top line replacements would work most excellent in replacing your pots. Heck.. it's worth some food for thought and research. Your 727 is a workhorse and after all the work youve done on it so far, its worth checking out I'd think.

 

[33&athird]

Thats' because the SX-525 is more of a classic than it's bigger brothers LOL- bigger isn't better...

...And... unless youre wanting to try and keep your 727 all stock, and/or actually try and find stock replacements, it's time to start thinking about what modern day top line replacements would work most excellent in replacing your pots. Heck.. it's worth some food for thought and research. Your 727 is a workhorse and after all the work youve done on it so far, its worth checking out I'd think.

, you may have a point there!...new pots would be a good idea, probably easier in the long run, but difficult to find drop-in replacements for. Certainly something to think about.

And to Mark, I've been thinking, and talking with my father about this, how could the relay cause imbalance?...if its activated, shouldn't all things be equal?...or is it too low a level to fully engage?...not a big question, just wondering:scratch2:...

 

[markthefixer]

, you may have a point there!...new pots would be a good idea, probably easier in the long run, but difficult to find drop-in replacements for. Certainly something to think about.

And to Mark, I've been thinking, and talking with my father about this, how could the relay cause imbalance?...if its activated, shouldn't all things be equal?...or is it too low a level to fully engage?...not a big question, just wondering:scratch2:...

Contacts burn, things wear out. There IS something called contact resistance, it increases over time, and it can end up being the most unlinear gawsh-awful transfer curve you've ever encountered. Corrosion, carbon, burned metal oxides, burned corrosion products- arrrrghhhh.... nothing's perfect

I've abrasively cleaned relays, only to have the same problems crop up weeks or months later.

I DID suggest bridging the contacts to see if the effect can be eliminated.