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.

   

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. 

De nada. I'm sure I won't be the only one faced with such problems.

 :dbtu:

Enzo and Phil,

Many thanks for your advice. I took the tank out and checked the cables attached. They did.

With the reverb up, I bounced the springs and sound indicated the out was OK, so I checked for broken connections or bad solder joints. All looked fine.

I ran my multimeter over the in and out and got 50 and 200 ohms. So I disconnected the cables from the tank and gave the connections a really good clean, including running some 0000 wire wool around the outside portion of the connectors on the tank and what do you know? This was where the problem lay.

Once I had a better connection, not only did the reverb work, the hum was almost totally removed.

Thanks for the helps, gents. It gave me some focus and I now have a far better understanding of these units, now.


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Quote from: substatica on June 24, 2018, 08:54:15 AM
Anyone have (and willing to part with) or know where I can get a couple of these wacky 70's Yamaha knobs from a YTA-95? Or know some other amps that used them?

Never seen them on anything else. Could you find similar and cut a section out as a stopgap?


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Quote from: Enzo on July 21, 2018, 08:50:40 PM
On each end of the reverb springs is a coil.  That is called a transducer.  The two wires to the jacks are coming from that coil at each end.  If the coil wires break, you can detect that with your ohm meter.

SO with the cables removed from the reverb unit, measure resistance across each jack.    I don't know what resistance you will find, it could be 2 ohms or 200 ohms.  But what we don't want to see is an open indication.  That would tell us a wire is broken inside the reverb.   It will either be good or open, it won't be "wrong".

Thank you, Enzo.


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Quote from: Enzo on July 20, 2018, 10:21:58 AM
Or the coil on the reverb is open.

OK, not sure what that means, but I'll look it up. Thanks again.


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Quote from: phatt on July 20, 2018, 09:12:45 AM
Sounds like the pickup from tank section is disconnected.
The cable may look intact but it's likely lost ground connection which is why it hums so bad. Similar situation when you unplug your guitar lead causing no signal *Open circuit* causing hum, really obvious with the gain high.

Just by gently wiggling the cable at the tank plug you may get signal.
If you get intermittent reverb then it's most likely the plug.
They are mostly small RCA type plugs and often break inside the plug. the plug looks like the common sealed type and not fixable so you may have to replace that plug.

The other possible stuff up is the input and output cables have been reversed this can also cause bad hum and little or no reverb sound.
Easy to check,, just swap them over.
Phil.

Thanks, Phil. Yes, they are the typical RCA type plugs on the reverb. I'll check those out as you suggest.

I had thought to switch the input/output cables, but the lengths suggested they'd been installed that way. I won't assume and double check.

Might it be at the other end? The revert cable terminate in 2 x 2 spade fittings that attach to the PCB. I suppose someone could have switched them by accident.


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I picked up this amp for not very much as it wasn't working properly. From the description, it sounded like dirty pots so I took the plunge and bought it.

After giving it a thorough clean, the amp turns out to be not a bad amp – the 12" speaker undoubtedly helps – and all the issues were resolved. Except one.

When you turn up the reverb knob from off, a hum is gradually introduced. It becomes very loud at maximum, though I would never use reverb at that level.

The chances are I would never use the on board reverb, either, instead use EH Holy Grail Plus. However, I'm not planning on keeping this amp and would like it working fully to maximise the return as I sell these kinds of items to raise money for charity.

I cannot find a schematic – and I have looked – but I have attached some pics of the chassis and amp and here is a link to a piece of video demonstrating the problem.

https://youtu.be/kYj17XQkhdI

One thing I can tell you is the cable on the reverb is securely plugged into the tank and also the PCB. Whether they're the right terminals, I can't tell you.

Though I have done a lot of reading and YouTube viewing since my last post, I am an electronics novice and haven't a clue, so any tips gratefully received.

Quote from: Enzo on November 05, 2017, 03:18:07 PM
Yes. grounded is grounded, it isn't like huge currents are flowing to require heavy wire.

It prevents noise, mainly hum, and I see no way that it matters to anything shorting to anything else.

Thanks again, Enzo, most enlightening. Makes me think it would be worth firing it up and if works, replace the damaged pots and generally tidy it up.


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Quote from: Enzo on November 05, 2017, 11:29:31 AM
Much of the time, the metal pot cover grounds itself to the chassis via mounting hardware, but not always.  By running a hard wired ground strap across the pot covers, we can make SURE they are grounded.  If they are not grounded they are limited in their shielding ability.  By grounding them, we are shielding the pots from radiated noise or signal.

Thanks for the response. I can get that, but doe you mean they will be grounded to each other and therefore the chassis?
And is that just to reduce interference or to prevent shorts? The chassis is mimimal, just a plate with another plate carrying the transformer and capacitors.
Though running across each pot, apart from contact with the face plate, there is only a small wire running from the circuit board to the first of the pots. Would that be sufficient to ground them

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Quote from: Jazz P Bass on November 05, 2017, 11:25:04 AM
Yeah, that's a 'ground' buss.

Not too sure about the slave.

Thanks for the comment.

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I picked one of these up recently, mainly for an Eminence speaker that had been fitted bit if operable after a few fixes, I could pass it on.

I'm no electrical expert, but I had a look inside and apart from the easy replacement of pots that have had shafts snapped off, it all looked pretty clean.

However, there are two things I am a bit stumped on. Firstly, someone has wired one of the speakers from the slave socket and I can't think why.

The other thing is that each of the pots has had a continous piece of copper strand soldered across all the pots. Is this a backup groubd because you coukdnt trust the FDR electrics or possibly to resolve a grounding issue?

Any help gratefully accepted.

The model is identical to a Sound City RC100 and a Vermona Regent (the model the others sprang from and were renamed for export).

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