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Restoring and Cleaning Amplifier Internals

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pkalder

New Member
wire and oxidation.jpg
I've come across a Pioneer SA-510 that was kept in the garage as an amplifier. It started "acting weird" so it was given to me. I respect the vintage tech, and want to bring this thing back to life for normal use in a cared for environment. It's got 2 problems.

  • It is oxidized inside. Rusted on wrapped terminals. (Red square)
  • Two wires are broken. (Red circle, only one shown)

Owner said that it had been working last time he turned it on but was acting weird. This was almost 6-8 months ago.

As for the oxidation, when I open it up, it smells acidic. Like a bag of gummy worms. It was not close to the ocean, but it is very humid and hot in our area. There appears to be no batteries or leakage. The wire wraps are oxidized to green and there are two wires that are broken. You can see the oxidized wraps and one broken wire in the close up picture. Here's my plan, and correct me if I am wrong.

I plan to clean the boards with 90% or 99% alcohol and detergent, then alcohol and baking soda (to stop the oxidation/acidic smell), then a final flush. Next step, I plan to resolder over the oxized wire wraps as stated in the following thread.

https://audiokarma.org/forums/index.php?threads/tutorial-deep-cleaning-an-amplifier.258899/
"Many Japanese amplifiers used a wire wrap connection system on the PCB(s) (consisting of a tinned pin, soldered onto the PCB and the wire conductor twisted around it in a tight fashion). This system usually oxides over the years and makes for intermitted or bad electrical connections. These connections can be “reestablished” by simply flowing a bit of solder over the wire and pin."

This doesn't seem like a correct fix. A full removal and resolder of nonoxidized wire, if there is any, would seem to be the best. Does solder restore oxidized terminals?

Then I plan to solder on a whole new small loop wire for the broken two in the pictures. I don't know why they aren't a simple conductive track like the others on the board. Maybe they needed a higher voltage. Here are my concerns.

  • Is the above a good attack plan?
  • If the broken two wires are oxidized at the break point, is ever other wire oxidized under the sheathing? Will this change the resistance? Should I replace every wire?
  • In the pic, there are multiple PCBs and a Flouroscope display. Do I separate all this for cleaning? This will be very time intensive. What if It doesn't work currently? Can I turn it on or will the broken wires risk damage?
  • There is the transformer and multiple wire wrapped choke inductors. Will 90% alcohol ruin these, trapping distilled water?
  • Should I apply new thermal grease to the heat sink and MOSFETs?
  • It doesn't appear too dirty in the picture, but it definitely feels a little oily, or waxy and this combined with the citric acid smell worries me. Should I just skip the alcohol/detergent/baking soda clean and do only resolder oxidation and wire repair?
Thanks all! I know I typed a lot. Here's the amp. 20190815_145922.jpg
 
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pkalder said:
Then I plan to solder on a whole new small loop wire for the broken two in the pictures.
Click to expand...
Check with the service manual that snipped wires may be a bias ( idle current ) adjustment technique.
 
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Fantastic. Thanks Avionic. I'll peruse for a manual and check the bias adjustment possibilities. I'm still new to this, such as bjt vs mosfet etc, but this stuff is so neat. I really hope I can get this thing restored.

In addition, i did read a technique online about vinegar oxidation control and neutralization with Sodium bicarb. At this link. https://www.instructables.com/id/How-to-perfectly-clean-wires-in-minutes/
I think resoldering over would be easier than two acid brushes solutions and time. Apparently the wire wrap is cold welded, so restoring is more for exposed wire and stabilization unless oxidation separated the weld.
 
pkalder said:
think resoldering over would be easier
Click to expand...
With all that patina and oxidation I really doubt you will have successful luck with flowing new solder. The new solder won't stick. You would be better off. removing the wire wrap pins from the circuit board and soldering the wires directly to the circuit board though the wire wrap pin holes.
 
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Avionics - "Better off flowing new solder"

This is what I want to do, then with the wire connections off I could give each pcb a light brush at least with 99% alcohol. I'm worried I'd solder one to a wrong pin and blow the amp. I'm thinking a lot of pictures for resoldering all the wires back in place.

I'm thinking I should turn it on first and make sure it works, but I'm worried something might blow, and my electronic skills are very novice.
 
Thank you watt hour. I've got the parts. For the dim bulb tester. I'll try to throw this together to have on hand.
 
pkalder said:
Avionics - "Better off flowing new solder"

This is what I want to do, then with the wire connections off I could give each pcb a light brush at least with 99% alcohol. I'm worried I'd solder one to a wrong pin and blow the amp. I'm thinking a lot of pictures for resoldering all the wires back in place.

I'm thinking I should turn it on first and make sure it works, but I'm worried something might blow, and my electronic skills are very novice.
Click to expand...
I'm refering to eliminating the pins entirely..
 
Ok hopefully dim bulb will be a go by tonight. I'm pretty confident this thing will power, but it will be good to have on hand. I had the corresponding pioneer radio that I powered on which worked in AM. No antennae tested for FM, it was in the same environment and condition (greasy feeling dust on pcb).

I'm thinking I am leaning toward a light wash with 99% isopropyl if this works instead of detergent or baking soda. Problem is, some resistors have the green oxidation on them as well. I dont know if climate control will halt this process, or if it needs a neutralization treatment.

I'll post back after dim bulb test, hopefully tonight. If anyone has a suggestion on pcb cleaning the light layer of greasy dust, or acidic smell (do old circuits normally smell like citric acid?), then that is a hangup for decision making.

Thanks for everyone's help.
 
I apologize to bump my own thread, but I have another question. I'm looking at sodablasting the speaker terminals, and maybe trying one of the wire wraps. I've heard vacuums can make a lot of static electricity, and wonder if this is the same with sodablasting. Also, maybe dim bulb test tonight.
 
The dim bulb tester and amp works! The vol knob is pretty scratchy even after contact cleaner. Im pretty sure it wasn't working well was because the phono inputs and speaker terminals are rusted. I'll have to separate these and sodablast them. I'm gonna do a light pcb wash with detergent and bicarb brush followed by an ipa rinse, because something is up. The inside smells pleasant and strongly acidic like lemons or sour blue raspberry candy.

wonder if this will work on the wire wraps
Click to expand...

That's what I think I'll do. I was planning sodablasting the terminals connected, but I'm paranoid about static electricity. I'll try a vinegar solution on a small brush, then neutralize it just to see how it works. I have a feeling I'll be doing avionics suggestion of direct solder, but I want to test and see. The vids show them submerging the wires for 5 min. I dont know if there would be enough solution to effectively work with just a brushing, but Ill keep everyone updated.
 
Most likely, the wirewrapped connections only have surface corrosion. The electrical connection is probably fine. If you really want to make sure, though, I would clean the wirewrapped connections with alcohol. Then I would use liquid flux and solder the wires to the post. I would not rely on flux-cored solder.

An advantage to doing this is that, if it does not work, you can always cut the wire and solder it to the board. But why start out with a time consuming fix when an equally good and quicker method is available?
 
ZLDMGJ180_3.JPG

I'm thinking of doing these mini dremel brass brushes before vinegar or flux/solder application. Would this cause static discharge, or buildup? The brass will be in contact, but the dremel isnt grounded. It seems it would be better than the sodablasting, but sodablasting would be fun to try and I believe very efficient.

I'm planning on making a novice YouTube video on all this.

EDIT: Never mind I have found out the following information. https://www.gordonbrush.com/static-electricity.php Copper and Brass are very close to the separation of triboelectric charge so it will not create as much charge. So dremel, brass brush, and copper windings are ok. Also
Conductive Brush Materials allow charges to move freely across their surfaces or through their volume. Charge placed in one spot on a conductive object will flow around the object so that all parts of the object are equally charged. If a charged conductor is grounded, charges will recombine [move to ground] until the object has no charge. Conductive materials have a low resistance to current flow. One common misconception is that conductive materials do not generate charges. This is because the dissipation of static charges from grounded conductive material tends to be complete and rapid. Ungrounded conductors can generate and hold static charges.
Click to expand...
 
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I wouldn't use those brushes anywhere near amplifier internals. One errant wire from the brush could cause some nasty shorts. Emery cloth is a better option if you really need to get in there.

I'm with RTally - I'm not sure I'd suspect the oxidized posts as an issue until you've traced something to that. In Pioneers, those wires are usually tightly wound around the posts and sometimes (always?) soldered so it's very likely the electrical connection is still sound.

I would clean pots and switches, check / adjust idle current, and test before you even start messing with those posts.

Mike
 
rave0035 said:
I wouldn't use those brushes anywhere near amplifier internals. One errant wire from the brush could cause some nasty shorts. Emery cloth is a better option if you really need to get in there.

I'm with RTally - I'm not sure I'd suspect the oxidized posts as an issue until you've traced something to that. In Pioneers, those wires are usually tightly wound around the posts and sometimes (always?) soldered so it's very likely the electrical connection is still sound.

I would clean pots and switches, check / adjust idle current, and test before you even start messing with those posts.

Mike
Click to expand...

I agree with loose bristle possibility. I'll can the brush idea. I do need a neutralization of the board, because below.

So a couple updates. I found out the amp was stored in a cabinet that also had pool chemicals in it. This explains the acidic smell.

Also, I moved a bit of the wire attached to the pin. The green oxidation flakes right off and uderneath is great looking single strand copper.

I'm making a wire dewrapper right now for the flouroscope, blue voltmeter, pcb. I'll remove this and clean the rest of the chassis.

But here's the question. Can a female pin header like in arduino or raspberrypi fit on these pins? Maybe molex from a power supply? Then no rewrap and easy removal in the future. Here's a pic.
 

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