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

[Philip Pemberton]

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/