- Fender amp chassis non conducting? - 4 Updates
- KDL40V5100 - 2 Updates
| Phil Allison <pallison49@gmail.com>: Jun 24 08:13PM -0700 Hi, just saw a circa 10 year old Fender " Blues Junior" amp. The chassis is of the usual plated steel, bent sheet construction - looks like thousands of others. But the surface is insulating - DMM does not continuity beep and shows megohms between adjacent points on the chassis. To get a ground connection you must use one of the threaded bolt holes for the back panel. Never seen this before. Surely this makes grounds on speaker jacks and even the safety ground connection unreliable. I have read that the plating may be " chromated zinc passivated " which is high resistance. Any ideas? ..... Phil |
| John Robertson <spam@flippers.com>: Jun 24 11:48PM -0700 On 2021/06/24 8:13 p.m., Phil Allison wrote: > I have read that the plating may be " chromated zinc passivated " which is high resistance. > Any ideas? > ..... Phil It might be an anodized aluminum skin. Anodized aluminum is very tough... John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
| Phil Allison <pallison49@gmail.com>: Jun 25 12:05AM -0700 John Robertson wrote: =================== > It might be an anodized aluminum skin. ** Completely wrong colour. > Anodized aluminum is very tough... ** I am very familiar with anodised Al, this is nothing like it. ..... Phil |
| "Peter W." <peterwieck33@gmail.com>: Jun 25 04:05AM -0700 > Any ideas? Blue tint? That would be your passivated zinc-based material. Yellow tint? That would be *chromated* material. No tint? See Applied Varnish. Given that the chromated material requires an extra step in the plating process, if this is a passivated plating (which I doubt) I suspect the former rather than the latter. Further, the latter is mostly done for corrosion protection, not insulation. Would Fender indulge in a costly process for corrosion protection? Note that the tints are quite subtle, but definite. Given that both are rather more costly than a simple applied varnish, of which there are dozens, I would look to one of those rather than something exotic. https://www.mcmaster.com/electrical-insulating-spray/ https://www.cable-technologies.com/productdisplay/3m-%E2%84%A2-scotch-%C2%AE-1601-and-1602-electrical-insulating-spray-1 Two of very many. Now, imagined it being done at an industrial level - the goal would be achieved at a very low cost. Note also that anodizing comes in many colors from clear to black and all between. https://www.ashevillemetalfinishing.com/2019/04/22/electroplating-and-anodizing/ But of all the options, that is the least likely as it is the most expensive. Somehow I do not see a guitar amp manufacturer doing this for something that is very nearly invisible to the end-user. Peter Wieck Melrose Park, PA |
| legg <legg@nospam.magma.ca>: Jun 24 03:21PM -0400 >into a useful standby mode. >Any ideas? >RL With a schematic for the power board only, I find a balance error, inverter error output lines and a backplane control input line. Balance error signals originate in the inverter balance assy where the flourescent backlight elements pick off their drive. A glitch every time the inverter turns on being normal - but this unit develops continually noisy balance error signals after about 4 seconds, which activates an npn/pnp latch to crowbar the 'backlight on' signal input line. If the latch is disarmed, the external processor shuts the board down anyways based on balance error output signal. If this output signal is overidden, the backlight still turns off after about 8 seconds - Don't know why. Possibly due to 'missing' balance error glitches from normal dimming action, if the programmer was being a real jerk. The balance board is mostly magnetics - 12 small ccfl inverter transformers being fed from the same main inverter on the power board. Inverter seems to run with no issues - lamps light ditto. Not sure how balance issues are being created - can't see any coupling caps to fail. Will have to check each load for current, somehow. There should be a 'run till you catch fire' jumper on this thing. RL |
| legg <legg@nospam.magma.ca>: Jun 24 04:55PM -0400 >into a useful standby mode. >Any ideas? >RL Found one of 12 panels giving abnormal feedback signals and disconnected it. Works for now. RL |
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