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Author Topic: Seized pots on a Marshall Guvnor Mk 1  (Read 258 times)

psafloyd

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Seized pots on a Marshall Guvnor Mk 1
« on: August 06, 2018, 09:43:46 AM »

This isn't such a noob query as it may appear on first viewing. In 30 years of playing guitar, I have never come across this particular circumstance. 

I have picked up my Guvnor which I haven't used for several years, but which is stored on a shelf in a bedroom, so no excessive moisture.

When I plugged it in, all the pots were seized. All of them. I have tried using some cleaner to free them off, but I am stumped as to why five pots should all fail at the same time and in the same way.

There is no apparent damage to the unit and it all looks otherwise good inside – no dirt or corrosion. The pots are not over tightened on the chassis, nor are they misaligned in some way that would prevent them from turning.

I was thinking perhaps the excessive temperature we have had this summer may have caused them to dry out and lock up, but all five pots at once seems rather a coincidence. 
 
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Estomagado

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Re: Seized pots on a Marshall Guvnor Mk 1
« Reply #1 on: August 06, 2018, 11:50:42 AM »

I have an old CCDB mixing desk with all but two pots seized the same way as yours. 180+ potentiometers to replace. Gorgeous! (And expensive...)

One tech once told me to heat the metal casing of the pot with a soldering iron for a few seconds while trying to rotate the shaft. According to him it can save a lot of pots, but haven't tried it yet. Has to do with dried lubricants.

Tubes suck!

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psafloyd

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Re: Seized pots on a Marshall Guvnor Mk 1
« Reply #2 on: August 06, 2018, 01:12:45 PM »

Thanks.

If I have to, I can replace them all. For an hour's work and a few quid, it will be worth it, if I didn't have a Drive Master in fully working condition. Still, I can always get my money back on the Guvnor if I replace the pots. Assuming I can, as they're small board mounted ones. I will have to check.

   
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phatt

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Re: Seized pots on a Marshall Guvnor Mk 1
« Reply #3 on: August 08, 2018, 05:36:04 AM »

It's not uncommon for pot shafts to seize up especially in a hot humid climate, even worse if you live near the sea. If the shaft and bushing are alloy it's even more likely to happen if not used for a long time.

Alloy against alloy is prone to lockup as alloy corrodes rapidly if no lube. If the lube dries out then corrosion grows rapidly and locks up the bushing.
The better quality pots use brass shaft in alloy case.
Just ask a fitter why you use dissimilar metals when making bushings and shafts. 8|

I'd just remove the knobs then get a can of RP7 or WD40 or what ever brand you have in your part of the world which is penetrating oil, some times marketed as water dispersant.
Leave it soak for an hour and then gently but firmly grab the bare shafts with pliers and see if they move. You have to be careful with slotted shaft and not to destroy the spline, if they are D shaft then less chance of messing it up.
I've saved a few pots over the years but sometimes they are beyond repair.
But give it a try.

As mentioned ,,give the case some heat as well.
Phil.
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psafloyd

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Re: Seized pots on a Marshall Guvnor Mk 1
« Reply #4 on: August 13, 2018, 10:59:02 AM »

Thanks, Phil. Points all well made and I completely agree. I was simply thrown by all five pots being equally seized – each utterly immobile – and I can only assume it has been the long hot summer we have had, particularly hen I was away and the house was locked up.

Have resolved now and will be posting to above response.

 
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psafloyd

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Re: Seized pots on a Marshall Guvnor Mk 1
« Reply #5 on: August 13, 2018, 11:02:33 AM »

Thanks, Estomagado, your idea worked a treat. After two sessions trying to get enough contact cleaner in to free them off, I only managed to get one working.

So, I got the soldering iron out with . nice fine tip and gave each a little heat, moving the point around after a few seconds. This loosened all of them off and I gave them a good dose of contact cleaner and they are now lovely and loose.

As I said to Phil below, I believe it must have been during the two weeks we were on holiday and the house was shut up as it must have been incredibly hot and completely evaporated any remaining lube.

Thanks for your help – another piece of kit resuscitated and put back to use.
 

 

Thanks.

If I have to, I can replace them all. For an hour's work and a few quid, it will be worth it, if I didn't have a Drive Master in fully working condition. Still, I can always get my money back on the Guvnor if I replace the pots. Assuming I can, as they're small board mounted ones. I will have to check.

 
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psafloyd

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Re: Seized pots on a Marshall Guvnor Mk 1
« Reply #6 on: August 14, 2018, 01:14:03 PM »

I'd try that trick with the soldering iron if I were you, as I found it most effective.

Thanks.

If I have to, I can replace them all. For an hour's work and a few quid, it will be worth it, if I didn't have a Drive Master in fully working condition. Still, I can always get my money back on the Guvnor if I replace the pots. Assuming I can, as they're small board mounted ones. I will have to check.

 
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