Re: Recent Marshall amps - safety issue.

jakdedert wrote:
Gareth Magennis wrote:
"N Cook" <diverse8@xxxxxxxxx> wrote in message news:g9oin3$so3$1@xxxxxxxxxxxxxxxxxx
Ron(UK) <ron@xxxxxxxxxxxxxxxxxxx> wrote in message
news:zKudnfrkAOO9IyLVnZ2dneKdnZydnZ2d@xxxxxxxxx
Eeyore wrote:
N Cook wrote:

Certainly for a model 1987X from 2006 and probably other recent models.

To save cutting small holes in the front fascia, to take the pot
ant-rotation lugs, they've cut them off and then not even secured the
pots
with star washers under the bush nuts or fascia. So even in careful
useage
the nuts work loose in a couple of years which is fine inside an
electric
quitar , just a rat's nest of knotted signal wires, no elf 'n safety
issue
there. But not for valve amps - needs a modification to stop each of
the
pots rotating and then bare connections touching.
Irrelevant probably. As long as there's no shock risk to the user, it's
fine.
I am a fairly experienced safety (and EMC) 'expert' btw. Ilearnt from
some of
the best. Since around 1987. You might say it makes the product
unreliable ?
Nought to do with safety.
I was quite wondering just how Mr Cook was intending to 'modify' the
mounting of pots - if the anti rotation peg is broken off, surely he`s
going to have to replace all the pots, and drill the panel to accept the
peg. Either that, or bodge something up? Either way I can`t see the
proud owner of a nice new Marshall amp being too chuffed about it being
modified from box standard in any way.

Ron
If you must know, replace plain washers with spring washers to reduce chance
of nuts slackening in the first place.

The 1mm tinned copper wire earth strap soldered to and across each pot is
not enough to stop, wire breaking and the pots rotating.

If in an electric guitar I replace the wire with flat copper strip, soldered
to each pot case, the sort of enamelled high current wire used in some power
transformers, with the enamelling stripped off..
In these sorts of cases, not wishing to add to any electrical hazard, 3/8
wide cable-tie with the fastener cut off , bridging the back of each pot,
and then 1/8 inch cable ties around each pot and the wide nylon.

If the owner does not like the appearance of such on the INSIDE of his amp,
FFS , well he can cut them off himself. But I am obliged to make some sort
of remedial works.

Traditional chassis mounted pots ie with loose wiring, not loomed, not pcb
mount ones.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



Well if my car came back from Kwik Fit with all sorts of extra wires and ties holding the exhaust on "better", I'd wonder WTF the fitter thought he was doing, and how much he had charged me for the priviledge.


Gareth.

I'm somewhere in between. Given a real issue with future reliability, I appreciate the attention paid. OTOH, it's a sales job for the technician as to the utility of such modification.

Many, many guitars (and other kit--I like that particularly British term) do indeed exhibit the loose pot--and loose jakc--syndrome. Most experienced players carry tools to tighten the nuts, forestalling or eliminating future failure...and consider it to be just another part of regular maintenance--like adjusting the bridge or filing frets. Less experienced players either have not seen the problem, or if so, believe it to be an issue with their particular instrument. They are the ones who would benefit most, and be hardest to sell.

As for the Marshall amp, again, many bought the unit on the strength of reputation. They're possibly not ever going to use it enough for the issue to exhibit. Those who do will either believe their case to be unique, or at least unusual. Pros will either appreciate the fix, or move on to more reliable brands (or more solidly constructed vintage originals).

So, I see the issue as a sales job. Unlike my vehicle (I look under mine regularly, but how many people do?), the mods made by Mr. Cook are only going to manifest in the absence of future problems, or in the telling by him. He'll either have to justify the extra expense, or simply absorb it.

As to the actual fix, all those outlined sound viable to me. I think I'd go for a multi-pronged approach. In fact using all of them is not without merit for a unit which needs to be bullet-proof in daily professional use--and these are the customers who will appreciate (and pay for) the extra attention.


Additionally, a 'chemical' solution seems indicated. Applying a thread locking compound to the nuts would help. 'Painting' the nut to the shaft and panel with something like fingernail polish is an effective, simple fix which requires no removal of the actual pot hardware...adding little shop time for the tech to justify the expense of.

Which is the approach I myself adopt.

If someone decided that they would take it upon themselves to 'rewire' my vintage Gibson, I`d be a might annoyed to say the least.

Ron(UK)
.

Relevant Pages

  • Re: Alternative grounding solutions.
    ... the shit grounded to the volume pot that needs to be. ... ground - and any bare wire will also go to ground). ... You might also want to order tone cap if you ... to the bottom tone pot and use 500k and .033 or .022 cap). ...
    (alt.guitar)
  • Re: MIG wire speed control problems
    ... certain that the problem is in the wire feed mechanism. ... I am trying to repair the wire speed control on a Century welder Model ... Unsolder the wires to the potentiometer and use a multimeter on the ... measuring between wiper and either end of pot. ...
    (sci.engr.joining.welding)
  • Wiring mod for Samick HJ-650 guitars (also applies to DA DH)
    ... I only changed the wiring on the neck pup. ... carefully--you will have to do some fishing if the wire comes off.. ... and let the pot fall into the guitar. ...
    (rec.music.makers.guitar.jazz)
  • Re: Do I need a solder pot?
    ... Barry Lennox wrote: ... For very thick wire, I use a Stanley ... > cable, not in the pot. ... I had a six inch round solder pot that i used to salvage dip ICs from ...
    (sci.electronics.design)
  • Re: Do I need a solder pot?
    ... For very thick wire, I use a Stanley ... >> cables) and that is the only time I use flux, ... >> cable, not in the pot. ... Its the only process where I ended up with more solder than ...
    (sci.electronics.design)