Vox AC30 , AC30CC2X, 2005

Roadie dropped it off the stage , in flight case, worked fine for another gig and then next time worked for 3 seconds. Sheared metal internal braces and choke looks decidedly drunken, almost sheared off, but all big lumps test cold ok so far. Could someone confirm that the 1W resistor R188 on the HT ac input should be

2.2 ohm ? Its not charred or any other indication of excess heating but I find the colour bands a bit confusing as red,red, gold,gold, white and is nowhere near 2 ohms now. Bit difficult to tell whether it is gold gold or silver silver bands until I disconnect the board and can get a better view. Is it a possible scenario that this R failed mechanically, but only partially, in the shock loading ? without any undue current loading/heating. Back-line manager swapped the o/p bottles with another amp and they functioned ok in the other amp and the speakers are ok.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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N_Cook
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Phone Korg, 01908 857130 then press the right buttons for Vox. They should email you a schematic. Doesn't this have a valve rectifier? Did the backline manager swap this also?

Gareth.

Reply to
Gareth Magennis

Any suggestions what to look for on scrapping off the coating of what maybe a mechanically failed one. Where to find the fuising bit to check for fracture versus fusing ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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N_Cook

Removed the grey coating and remnant parts of the metalisation/ MO sum to about 1.5 ohm. The joining section is about 1 x 1 mm with a neat hair-line crack across it and no sign of any heating there. So mechanical breakage, I will dig out my microscope and take a photo of it.

Before removing coating, was definitely 2.2 ohm markings with white band (if) for x16 presumably referring to that 1 x 1 mm section, so x32 violet banded one would have a something like 0.7 x 0.7mm intercept region and a green band x8 would have more like 1.4 x 1.4 mm fusing area.

Anyone care to give a reason for shock induced fracture just at that point?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

I suspect a Roadie dropped it off the stage.

Gareth.

Reply to
Gareth Magennis

Splurt! No no stop... you owe me a keyboard now!

Ron(UK)

Reply to
Ron(UK)

Putting my materials testing hat on - it probably suffered torsional failure. Wire ended 1W suspended off board, if one end swings one way and the other end swings the other then perhaps a torsional twist that is enough to part at the weakest point of the conductive strip.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

Think that was stated in the OP(?).

jak

Reply to
jakdedert

Well there's irony for you.

Gareth.

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gareth magennis

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Is a microscope view of the crack. Now viewing magnified it can now be seen the fault developement. The just left of centre part of the crack must be part of a crack that formed initially but enough current flowed in the other parts making touching contact until there was too much localised fusing.

1 to 1 marks the 1mm or so of conductor between the 2 straight line etching/millings ? into the conductor to form part spiral paths. The C marks the end of one of these formed breaks and there is another one on the other track , off the top left of the image, giving about 1 x 1mm central fusible conductor. Nowhere on the remaining conductor is there any discolouration due to overheating

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N_Cook

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