Fluke 289 battery pads ??

[darkstar49]

Hi,

I received a dead 289 a while ago, saw a blown cap on the board, replaced it, didn't fix the problem, and so it went in a drawer, where it remained for years.
Yesterday, I somehow unintentionally came across the meter, and thought I'd give it another try...

I immediately noticed the batteries were getting hot quite quickly (the meter was disassembled in the drawer)... on the board, the (+ & -) pads had a 'normal' resistance between them, but once the battery holder was installed, I almost had a short (just a few ohms) on the holder's pads !

Long story short, the problem was that the replacement cap is somewhat taller than the original, and has conductive pads on both sides (all around), which shorted with one of the holder's flat pads (see pics). The battery holder has in fact 3 contacts (45° inclination) that match those on the board, but also 3 'flat' pads, that get pretty close to the board once installed. Putting some tape on those just to test, fixed the problem.

Given the layout of the board, I absolutely don't get it 
What the heck are these flat pads good for ? They get damn close to components on the board, and there's no insulation whatsoever... doesn't seem like a sound design to me, but on the other hand, Fluke is typically doing things right... so am I missing something here ?

Comments welcome !

[Grandchuck]

Looks like the flat pads keep the travel to a fixed limit (thus provide support).  They allow only a limited amount of compression of the moving contacts.

[darkstar49]

Looks like the flat pads keep the travel to a fixed limit (thus provide support).  They allow only a limited amount of compression of the moving contacts.

agree... but I'd then have coated those with some insulation material, given the proximity with the board...

[Black Phoenix]

agree... but I'd then have coated those with some insulation material, given the proximity with the board...

If the parts are properly manufactured from factory, then no need to insulation material (although it is a good fail safe just in case) since they are for sure within tolerances. The question is if this are original parts/original replacement parts or if they are after market.

You said you received the 289 dead, it could had already someone messing inside and bended that part for some reason or changed it for some reason. You just received dead, you don't know (do you?) the past of it before it came to your hands.

Although I agree with you, I as someone who always look how something can fail, I would have added some rubber pads or insulation tape (even heatshrink is enough) to the design/BOM.

[darkstar49]

agree... but I'd then have coated those with some insulation material, given the proximity with the board...

You said you received the 289 dead, it could had already someone messing inside and bended that part for some reason or changed it for some reason. You just received dead, you don't know (do you?) the past of it before it came to your hands.

Although I agree with you, I as someone who always look how something can fail, I would have added some rubber pads or insulation tape (even heatshrink is enough) to the design/BOM.

When I got it, it had a dead capacitor, which I replaced with what I had at hand, which was 1) somewhat taller, and 2) had conductive pad all around each side, opposed to the original smd tantalum capacitor (kemet type, yellow/red), that had the conductive pads at its bottom only... so one of the battery holder flat pad shorted the capacitor once it was in place, which I didn't understand at the time... (I already had another meter, so I didn't spend much time on this, and the Fluke just went into some drawer...)

[Black Phoenix]

When I got it, it had a dead capacitor, which I replaced with what I had at hand, which was 1) somewhat taller, and 2) had conductive pad all around each side, opposed to the original smd tantalum capacitor (kemet type, yellow/red), that had the conductive pads at its bottom only... so one of the battery holder flat pad shorted the capacitor once it was in place, which I didn't understand at the time... (I already had another meter, so I didn't spend much time on this, and the Fluke just went into some drawer...)

So you already know the cause of it, but still I would insulate from factory that parts anyway.