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What to do about old degraded foam inside equipment (Ashly SC66a parametric)
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hymenoptera
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#1
29th December 2012
Old 29th December 2012
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What to do about old degraded foam inside equipment (Ashly SC66a parametric)

FedEx girl dropped off an Ashly SC66a parametric equalizer today, first thing I do, take her top off to find two big blocks of foam between the PCBs and chassis, and the years have really taken their toll. They're both dryrotted, "squishy" even, and pretty much break apart on touch, and I guess they need to come out or be replaced.

Is the foam from the factory? Can I assume this thing hasn't been open since 1979? What's standard proceedure for removing this stuff? Pick out what you can by hand and blow out the rest with compressed air? What does it do, and should I replace it with new foam when I'm done?

She's seen better days. Pots need cleaning. The caps are groaning on powerup and when whining while turning some of the freq pots. It's likely all electros will need replaced before she takes her place in the rack. Left it on and processing a signal all evening hoping that will be a temporary fix for the caps for now. Some other things will pop up needing attention I'm sure, but this foam has got to go before I can even take a deeper look.

Otherwise sounds great. So, what are my options, folks?
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What to do about old degraded foam inside equipment (Ashly SC66a parametric)-img_9757_sc66a_foam.jpg  
#2
29th December 2012
Old 29th December 2012
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Those foamies are factory, they were used to keep the circuit boards steady. If you notice, the circuit boards move a lot, I think they are only held on by the pot nuts.

Maybe try acetone or running alcohol to remove the melted Styrofoam?

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29th December 2012
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well, i painstakingly picked, brushed, and vaccuumed it all out. PCB leads look corroded where foam was touching in a few spots.might take some bus wire and jumper across two adjacent solder points

it's gonna be hell recapping this thing. all knobs will have to come off (34 i think?) and the each are held on with a set screw. ribbons inside are short and dont offer much room to work. wonder if i can cut or desolder one side and put on quick connects for each? wow, lots of work no matter how i do it.

fonrtunenately she sounds great. no more pot noise, and no more cap noise, for now. i think it just hadn't been used in a long time.

should i replace foam with something else to keep PCBs from moving?
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29th December 2012
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Test the traces with a dmm to see if there is any damage to the traces. If the resistance is very low don't worry about it. Clean the corrosion with 99% ISO alcohol. If the sound of the unit sounds good to you, don't brother recapping, wait until it gets some hum or sounds bad before recapping. It's a lot of work!

You could try securing the board with some plastic stand offs depends what you have available to you.

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29th December 2012
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thanks for the advice on recapping i won't do anything else to the sc66a until problems arise.

tested the traces that appear corroded and getting 0.1 ohms across adjacent solder points. for something more than 30 years old i guess it's a testament to build quality that it's never needed servicing.
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29th December 2012
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I've got one of those old ashley eq's as well with very scratchy pots. Tried to open her up but the screws are real shot. Do you have other pics of the guts, would love to see more of the circuitry inside. Good luck with your restore as well...
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30th December 2012
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more pics inside

Quote:
Originally Posted by daez View Post
I've got one of those old ashley eq's as well with very scratchy pots. Tried to open her up but the screws are real shot. Do you have other pics of the guts, would love to see more of the circuitry inside. Good luck with your restore as well...
you're in luck! while i already closed it back up earlier, I had taken some photos of the filters so I could study them later since I want to learn more about EQs and filters in general.

Op amps seemed to be all 4558's but I didn't really look at much more than the filter cards. There's a main board along the front, ribbons going off to each filter card where the pots are (8 filters in all), and ribbons going to the output card where the jacks are. The PSU also has it's own card.

These four pics that follow are all from the bottom access port since there's not much to see from the top (first pic OP post #1 is of the top). These four here all show details of the filter PCBs and components. Sorry, didn't get any of the power supply, mainboard, or output board.
Attached Thumbnails
What to do about old degraded foam inside equipment (Ashly SC66a parametric)-img_9776_ashly_sc66a_bottom.jpg   What to do about old degraded foam inside equipment (Ashly SC66a parametric)-img_9781_ashly_sc66a_filter_pcbs.jpg   What to do about old degraded foam inside equipment (Ashly SC66a parametric)-img_9780_ashly_sc66a_filter_pcb_bottom.jpg   What to do about old degraded foam inside equipment (Ashly SC66a parametric)-img_9784_ashly_sc66a_filter_pcb_top.jpg  
#8
30th December 2012
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The paper/copper ribbon interconnects are horrible- they are almost certainly brittle by now, and will likely fracture even with the most careful or removal. It would be less of a headache to just cut them to get the boards out easily, and replace them with new plastic ones that shouldn't break when you put them back in.

Looks like a nice eq, though!
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30th December 2012
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Replacing the paper ribbons with new ones might be a fun project some day. I have to admit I'm young, relatively new to electronics, and I've never seen these before.

Given that some of the ribbons are of the modern PVC type, can I assume that some work has already been done here? The quick connects on the power transformer leads (see: IMG_9776) also strike me as a modern addition. What look like scortch marks around the on/off switch suggest someone had to replace the switch and installed quick connects for "next time".
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scratchy pots

daez, for the scratchy pots try turning them back and forth the full range a few dozen times. Sometimes it works, sometimes it doesn't. On the sc66a it worked great for me!
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There is also a good fader lube that will get rid of the scratchy ness of the pots, I can't remember what it's called but will check next week when I am back. A little spray and a couple of full turns and they will be silent and very easy to turn. It's a lubricant that they use in the food industry for production machines.

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Might be thinking of Caig Deoxit.

But if so then I wasn't aware it was food safe. Might try some later on a sandwich just to be sure
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30th December 2012
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I don't drink alchohol (or "pop" for that matter) but isn't Everclear supposed to be pretty nearly 100% alcohol. I have heard that it is an excelent solvent for cleaning things as it leaves no residue when it evaporates. But apparently it is difficult to get.
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Quote:
Originally Posted by rcrowley View Post
I don't drink alchohol (or "pop" for that matter) but isn't Everclear supposed to be pretty nearly 100% alcohol. I have heard that it is an excelent solvent for cleaning things as it leaves no residue when it evaporates. But apparently it is difficult to get.
Back in the day, Everclear was 99% alcohol. It's lower now, at least in my state. I think they changed the laws here and you can only get a lower proof version, but maybe they only manufacture the lower proof version, I don't know.

I don't think I would use it either way, simply because there are products on the market designed specifically for electronic devices. FWIW.
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31st December 2012
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Hmm, might be time to pick up a fifth of liquor. For "research" purposes, of course.
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31st December 2012
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Quote:
Originally Posted by hymenoptera View Post
Hmm, might be time to pick up a fifth of liquor. For "research" purposes, of course.
Yesss... ring in the New Year with lots of research.
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