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Repairing conductive rubber contact switches

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Repairing conductive rubber contact switches

Postby BillB » Sun Aug 18, 2019 10:05 am

Hi folks. I think we have touched on this before, but I couldn’t find it on the forum. I have a Yamaha PSS-780 (basic FM synth) which mostly works fine, apart from the drum pads along the bottom of the keyboard, which barely respond. Having just opened it up, it is pretty mucky inside, with obvious dust and hair on all of the rubber pads.

I have seen various fixes online:

1) Just vacuum and clean contacts/pads with isopropyl alcohol.

2) Apply conductive paint. Two examples:

https://www.ebay.co.uk/itm/MUSIC-KEYBOA ... 1662188354

https://www.amazon.co.uk/Restore-Conduc ... ref=sr_1_1

3) Replacement pads - example:

https://www.ebay.co.uk/itm/Conductive-r ... 2169697758

4) Cut and glue tin foil to each pad!

So I am inclined to try 1) and see what happens, as I could do it right now, but would like to know what folks think would be the most effective fix.
BillB
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Re: Repairing conductive rubber contact switches

Postby N i g e l » Sun Aug 18, 2019 11:57 am

BillB wrote:3) Replacement pads - example:

Not seen those before, they look useful .

I had a similar problem with my mmt8.
The buttons were all on 1 rubber sheet. The under side of each button was carbon coated and when pressed down, bridged contact across HASL PCB tracks which were interlocking fingers..
The carbon on the buttons had worn down and the solder on the PCB tracks had been pushed thinner and oxidised. A temporary solution was to reflow the tracks and clean the carbon pads with mildly soapy soft water.

Long term my solution was to fit proper switches – very low profile surface mount types @ < 10p ea. Effective but time consuming.

If cleaning the unit note that electronics can be static sensitive and vacuuming can generate static [especially Dysons]. Alcohol can reduce the flex in rubber material over time.
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Re: Repairing conductive rubber contact switches

Postby Watchmaker » Sun Aug 18, 2019 12:19 pm

I caution against alcohol on rubber. Hard to know which compounds are being used. At most warm water and a gentle touch.
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Re: Repairing conductive rubber contact switches

Postby BillB » Sun Aug 18, 2019 1:21 pm

N i g e l wrote:Long term my solution was to fit proper switches – very low profile surface mount types @ < 10p ea. Effective but time consuming.

That is a thought for the more functional switches (start-stop etc) although the pads are a distinctive part of the look of these PSS’s so ideally would like to get them working as is.

Re-reading the manual, it receives MIDI for the percussion sounds on Ch16 (before Roland established Ch10 as the default for perc?). It is velocity sensitive over MIDI, unlike the pads, so probably not worth bothering to get the perc pads working.

Thanks both for the warnings about alcohol. More likely to be heeded than the warnings I got from my Mum back in the day...
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Location: East Yorkshire


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