Pioneer SX-1250 - Restored, but essentially useless

onwardjames

onwardjames

Hoardimus Maximus
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Hello everyone!

I have a restored SX-1250, got a full, ground up rebuild/recap back in 2014. When I got it back, I was very impressed with the work, but there was some static in that Alps sealed pot. I asked my tech, and he said "it was sealed, so I couldn't do anything with it."

I am not complaining about the quality of work otherwise....but it is essentially useless. Even leaving it on for days and working the volume back and forth, it's horribly noisy and drops the left channel a bit.

I am desperate. Has anyone had luck cleaning that infernal master pot?

Thanks, everyone.
 
Your going to have to remove the pot from the board and dissemble it. I've see a few of these that the carbon track has wore out, no repairing that. You can give it a try or troll the Bay for a replacement and hope it's in good shape. ALPS still has 50K Blue pots that may work with some modifications.
 
embrown057 said:
Your going to have to remove the pot from the board and dissemble it. I've see a few of these that the carbon track has wore out, no repairing that. You can give it a try or troll the Bay for a replacement and hope it's in good shape. ALPS still has 50K Blue pots that may work with some modifications.
Click to expand...

Thank you greatly. However, that's beyond the scope of my abilities.

Damn these needy receivers. This one has been a continual headache for me since getting it back in 2008.
 
Welp... you didn't hear this from me, but I've seen the occasional sealed pot with small holes drilled in it for to spray in some deoxit. They were covered in black electrical tape to keep crud from working it's way in there. Wasn't a 1250, but a lesser piece like a Rotel preamp or something like that. It's time consuming, but I usually pull the pot and loosen the screws enough to get some deoxit in there. If the pot isn't mounted to a circuit board, it isn't very labor intensive at all.
 
I have also found that if you remove the front panel, and pull the control amp board (nuts on the controls and screws for the switches, you can unscrew the 2 screws that hold the alps together. push these skinny long screws out of the control, being careful not to lose the small nuts in the back. I have found that I can "Split the sections" just enough to get some faderlube in the to clean it, without having to unsolder it. I am nervous about unsoldering those controls as the contact are very brittle and break easily. Then reassemble and put it back together and test

But before doing all of that, test with a voltmeter and make sure you don't have any DC on any of the volume control contacts. If you see anything above 8mv to 10mv, suspect that one of the coupling caps is leaking DC.
DC on the control will give the same symptom as a "dirty" control, and at times worse. If you find some DC voltage, Suspect C9, C10, C11, and C12. Also check to make sure they are installed with the correct polarity, as I have found board marking errors in pioneers. Those caps are used as a pair with the Negative leads tied together electrically. So the two 22uf caps (C9 and C11), as well as the two 22uf caps (C10 and C12), actually become the same as a 11uf bipolar cap in that way. Seeing that you had a full restore done on it, there could have been an issue with the install of those caps. C9 and C11 are for the left channel and C10 and C12 are for the right channel
 
willyrover said:
You could create a small hole in each section of the pot with a thumb drill or a pin file. Go slowly and keep vacuum on it so the plastic bits don't fall into the pot.

Deoxit through the hole.

Cover the hole with a piece of tape or dab of silicone.

View attachment 1385532
Click to expand...
If you do that be very careful. I bought a Kenwood Model 500 someone had done that to and they destroyed the pot. I think they used their Milwaukee hammer drill on it.

P1011236.JPG

P1011256.JPG
 
Same style of pot that's in an MCS 3275. As someone posted earlier I was also able to remove the screws and separate the sections enough to get deoxit in and clean it. Worked for me anyways.
 
I've never even considered drilling one of these. You can get cleaner into them, right where the solder tabs come through. I use the aerosol, and it makes a big mess, but it works. I only had taken this one apart to repair it.

P1011250.JPG
 
Tom B said:
I have also found that if you remove the front panel, and pull the control amp board (nuts on the controls and screws for the switches, you can unscrew the 2 screws that hold the alps together. push these skinny long screws out of the control, being careful not to lose the small nuts in the back. I have found that I can "Split the sections" just enough to get some faderlube in the to clean it, without having to unsolder it. I am nervous about unsoldering those controls as the contact are very brittle and break easily. Then reassemble and put it back together and test

But before doing all of that, test with a voltmeter and make sure you don't have any DC on any of the volume control contacts. If you see anything above 8mv to 10mv, suspect that one of the coupling caps is leaking DC.
DC on the control will give the same symptom as a "dirty" control, and at times worse. If you find some DC voltage, Suspect C9, C10, C11, and C12. Also check to make sure they are installed with the correct polarity, as I have found board marking errors in pioneers. Those caps are used as a pair with the Negative leads tied together electrically. So the two 22uf caps (C9 and C11), as well as the two 22uf caps (C10 and C12), actually become the same as a 11uf bipolar cap in that way. Seeing that you had a full restore done on it, there could have been an issue with the install of those caps. C9 and C11 are for the left channel and C10 and C12 are for the right channel
Click to expand...
I have done this pot separation cleaning with good success. I’d recommend following these instructions. Tom knows his stuff.
 
THANK YOU EVERYONE for you replies. I think I might give a shot at getting a little deoxit in there.

I think the pot has just become very corroded, so I'll tear it apart and see what I can do.

Again, thanks so much, everyone! This was a gift from the wife, so.....
 
Drilling may work but is a risky deal. The only Alps I worked on was on My Pioneer SA-900II. I did as Tom B described roughly. I loosened the bolts enough to separate the slices, but not pull the bolts out. I separated each slice and used Deoxoit D-100 mixed 50/50 with low aqueous isopropyl alcohol in a needle bottle. In each slice, I would generously squirt the mix and then cycle the knob rapidly and for a good amount of time for each slice. Keeping the blue workshop paper towels underneath, I avoided having overleak. After a good long wait and some more cycling, I used D-100 by itself for a layer. Again a waiting period. I followed the same full strength application of F-100 Fader and then Caig Shield. That was about 10 years ago and I still have had no issues. When I describe the %0/%0 mix in the past, Caig gave me a like on my post. This mixture is great for flushing badly gritty pots, etc..

I hope you will try this method as it works well and your reputation would help spread this around AK and elsewhere. I too was very wary of pulling the pot apart; so my method is a good stop-gap method. I have never used D-5, because you run a chance of dissolving the contact's attachment inside the pot. I have never had a backfire with my method. Good luck to you.
 
Tom B said:
Seeing that you had a full restore done on it, there could have been an issue with the install of those caps. C9 and C11 are for the left channel and C10 and C12 are for the right channel
Click to expand...

While I sincerely appreciate this technical info, I'm pretty certain this has been around since before the restore.

The guy who did it is a respected tech here on these boards, and I hate to sound like I'm complaining, but it is a bit frustrating to drive 6 hours to get to someone's house, drop it off, wait 4 months, drive 6 hours back to pick up, only to have noise in this damned pot.
 
LesE said:
Does the Volume control noise drop when the Muting is activated? If it does, it may support @Tom B 's suspicion of DC.

The biasing of Q1-Q4 on the Flat Amp is such that the DC appearing at C9 & C11 can change from the spec (0V) depending on the gain of the replacement transistors. So as Tom suggests, an incorrectly oriented capacitor (C9-C12) can allow a significant DC voltage to get through to the Volume control. Since the Muting is in between the two, it would drop the voltage somewhat if it is in fact DC getting through.
Click to expand...

It does it, even with muting engaged and the volume at a dangerous 12 o'clock. It's grit and corrosion in the pot, as once you've found your preferred volume level, it tends to be okay. Just don't think you're gonna alter it without some degree of headache.

@KingBubba I plan on using that method you described. I also will not use D-5 due to what you stated. Thank you, sir.
 
leesonic said:
How easy is it for you to remove the pot and send it to one of us? Is it on a seperate board with wire wraps on it?

Lee.
Click to expand...

Lee, you're always so generous with your time and expertise. I have every hope that one day I can hand deliver that M504 and P304 for a full rework via your skills. I haven't forgotten. Me and the wife are due a trip up the east coast, anyway.

Thanks, man.
 
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