[volt-nuts] Solartron 7150plus - Chasing AC gremlins

[m k]

How stable are the power supplies?

> Date: Fri, 7 Dec 2012 22:56:40 +0000
> From: philpem at philpem.me.uk
> To: volt-nuts at febo.com
> Subject: Re: [volt-nuts] Solartron 7150plus - Chasing AC gremlins
> 
> There aren't any electrolytics in the AC signal path.
> 
> Cooling the AD637 causes the displayed voltage to drift but doesn't
> clear the calibration error. Power cycling the unit will allow AC
> calibration to complete. None of the other parts on the "suspect list"
> have any effect.
> 
> I've resoldered everything in that path - from the Coto relays through
> to the amplifier and RMS-DC converter. No luck - it's still misbehaving.
> The readout on the 0.2V setting has dropped 200 counts (0.00200) in the
> space of a few minutes. It's reporting "GOOD" for calibration, but I
> expect that'll change when it warms up.
> 
> There's a Philips 100V / 2.2uF metallised polyester capacitor (C17)
> connected between pins 8 and 9 of the AD637 and a second one filtering
> the output via a 27k series resistor.
> 
> I'm starting to think I'm getting a bit out of my depth... in any case
> this is going to have to wait until tomorrow night as I have a to-do
> list a mile long and precious few hours left to finish it off!
> 
> It looks like most of the circuit sections are linked with passive
> components and can be isolated by desoldering one or two leads. Signal
> injection and tracing is next on my "try that!" list.
> 
> Thanks,
> Phil.
> 
> 
> On 07/12/12 18:59, m k wrote:
> > 
> > How about a leaky electrolytic? look for dried out ones, give the cans a quick spin, if it actually rotates it has leaked and dried out.
> > 
> >> Date: Fri, 7 Dec 2012 09:48:13 -0800
> >> To: volt-nuts at febo.com
> >> From: eb at telight.com
> >> Subject: Re: [volt-nuts] Solartron 7150plus - Chasing AC gremlins
> >>
> >> I would first look at the electromechanical aspects. Are there any 
> >> relays or connectors in the signal path? Next would be any device 
> >> sockets - they can be exercised by rocking the parts a little. Next 
> >> would be to inspect carefully for bad solder joints, corrosion, and 
> >> signs of physical damage. Then consider the actual electronic components.
> >>
> >> Ed
> >>
> >>
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> 
> 
> -- 
> Phil.
> philpem at philpem.me.uk
> http://www.philpem.me.uk/
> 
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