Silver St888 Volume Pot

Chester Draus

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May 19, 2019
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Hey all,

This is my first post since joining up. I've recently picked up a Silver St888 SPACEMASTER 11. I've got issues with the volume pot

Symptoms are one channel starts very loud and the other just stays quiet. Resistances are all other the place and cleaning doesn't seem to help :(. I think I have the channels and 1 is about 20k, the other about 100k

Unfortunately it's not a pot I can seem to find a replacement for, numbers on the pot are as follows;

50306119 m50kb 25j

It's even has 7 pins!! Why! Haha

I've just purchased a manual, hopefully it has some schematics. Any help would be greatly appreciated

Thank you :)
 

Chester Draus

Member (SA)
May 19, 2019
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Thanks for the reply hopey!

No problem, I'd say the tracks are pretty cactus by what's goin on.

Any advice in regards to servicing the pot?
 

Chester Draus

Member (SA)
May 19, 2019
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Not the best photo I know, just took it quickly on my way out to work.

I will get better photos and measurements tonight if required.

In regards to loudness there is no physical button.

Thanks again
 

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Chester Draus

Member (SA)
May 19, 2019
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Unfortunately I've given that a go with CRC CO Contact Cleaner, it reduced the scratches and increased volume. After the clean I could hear the pot physically squeek when adjusting it. As a last hope I tried using some CRC 2.26 in a syring to help it. Still no good. I'd say the tracks are stuffed :(

OK sooo I found out why I have these strange issues... I found a wiper in the bottom of the case, I'm guessing from one of the volume pot tracks.
 

hopey

Member (SA)
Dec 28, 2014
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Melb AU
Chester Draus said:
Thanks for the reply hopey!

No problem, I'd say the tracks are pretty cactus by what's goin on.

Any advice in regards to servicing the pot?
You need to remove all solder from the 7 pins with a sucker or wick. Undo the shaft lock nut and remove the pot from the board. Using a small screw driver bend the four metal tabs 90 deg and remove the base. now you can access the carbon track clean with alcohol and cotton swab. Clean the metal fingers with fine grade sand paper. Grease and reassemble.
 

HRmeteohub

Member (SA)
Mar 19, 2017
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Croatia
hopey said:
Any advice in regards to servicing the pot?
You need to remove all solder from the 7 pins with a sucker or wick. Undo the shaft lock nut and remove the pot from the board. Using a small screw driver bend the four metal tabs 90 deg and remove the base. now you can access the carbon track clean with alcohol and cotton swab. Clean the metal fingers with fine grade sand paper. Grease and reassemble.
I second that.
There is no way to be sure that is is clean or the carbon strips are failed/worn out without disassembling it.
I would also like to see the photo of carbon strips of the potentiometer after cleansing.
 

Chester Draus

Member (SA)
May 19, 2019
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I'll definately give the pot a service and get back to you all, thanks for the advice.

I do have one more question, are these units sought after / worth restoring? (I can't find too much info on them) I'd love to restore it as I do have respect for old audio gear and think this thing is pretty unique with the 11 band tuner, but I just want to gauge to what lengths I should go. Thanks again
 

hopey

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Dec 28, 2014
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It's all about condition I think the Silver Brand is much better than most, older the better.
 

Chester Draus

Member (SA)
May 19, 2019
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Bad news, the pot is dead. Appears to be either my own or a previous owners contact cleaner has attacked the plastic and all the wipers have become dislodged, hence the crazy resistance readings...

I'll start scouring the internet for a replacement 40k 7 pin pot. Anyone have any suggestions where to start. Mouser or RS online?


The casualty
 

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docs

Member (SA)
Jun 26, 2010
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Ok take a step back.

The wipers can definitely be re glued in to place, no problem there.
I would first of all test continuity on the tracks from one side to the other because there should be continuity.
You can then determine which tracks are not "connected".
There could be breaks at either the point which the pin connects to the board or where the track runs across the board itself.
You must determine where the fault lies but if the fault does lay with the tracks and lack of continuity across them or to the pins, it definitely can be restored.
 

Cpl-Chronic

Member (SA)
May 14, 2012
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Windsor, Ontario, CANADA
Chester Draus said:
Unfortunately I've given that a go with CRC CO Contact Cleaner, it reduced the scratches and increased volume. After the clean I could hear the pot physically squeek when adjusting it. As a last hope I tried using some CRC 2.26 in a syring to help it. Still no good. I'd say the tracks are stuffed :(

OK sooo I found out why I have these strange issues... I found a wiper in the bottom of the case, I'm guessing from one of the volume pot tracks.
Uh, also, that contact cleaner is probably the worst thing you could have done. I made the same mistake, once & only once. The cleaner strips the lubrication & actually eats at the tracks. That stuff actually has a slightly corrosive action similar to WD-40 & strips the lubircation from the pot & the wipers will not survive long either...It kills me how many posts on forums wrongly promote WD-40 as a volume pot/slider cleaner because the volume worked for 5 minutes before it crapped out forever..
 

caution

Member (SA)
Mar 25, 2014
2,498
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Boomboxery
This is likely the same 50k Panasonic potentiometer used in many boxes, most of which wouldn't be worth sacrificing just for that, but some '90s-era Panasonics would be. However, some of them have different shaft lengths and mounting brackets, so you'll have to re-use your bracket and possibly shorten the shaft. Check my comments on this thread for a list of candidate boxes. If you're curious of the different styles check this datasheet.

It's possible to glue the wipers back into place, Check this thread for its six-pin cousin that I fixed.

There are seven pins because it has a loudness tap, which engages a filter for the first half of the dial for more bass at lower volumes. So you have essentially two pots inside with a common ground, for a total of five pins, then a tap pin for each channel.

 

docs

Member (SA)
Jun 26, 2010
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Try repair existing before sourcing a replacement.
I’ve repaired numerous pots with conductive paint to restore continuity. Just match each channel to get the ohms and it’ll be fine.
 

hopey

Member (SA)
Dec 28, 2014
1,262
278
83
Melb AU
Cpl-Chronic said:
Unfortunately I've given that a go with CRC CO Contact Cleaner, it reduced the scratches and increased volume. After the clean I could hear the pot physically squeek when adjusting it. As a last hope I tried using some CRC 2.26 in a syring to help it. Still no good. I'd say the tracks are stuffed :(

OK sooo I found out why I have these strange issues... I found a wiper in the bottom of the case, I'm guessing from one of the volume pot tracks.
Uh, also, that contact cleaner is probably the worst thing you could have done. I made the same mistake, once & only once. The cleaner strips the lubrication & actually eats at the tracks. That stuff actually has a slightly corrosive action similar to WD-40 & strips the lubircation from the pot & the wipers will not survive long either...It kills me how many posts on forums wrongly promote WD-40 as a volume pot/slider cleaner because the volume worked for 5 minutes before it crapped out forever..
It's not contact cleaner! It has suffered a pile drive from the box falling over that's why the locating pins for the fingers have sheared off. Just glue them back into position.
 

caution

Member (SA)
Mar 25, 2014
2,498
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Boomboxery
Nope, the feelers fall off from the constant stress the feelers impose on the plastic rivets by pressing against the tracks. This occurs plenty with well cared-for boxes.