[Boatanchors] [collins_radios] Simpson 260 Assistance Needed

[Steve Byan]

On Sep 29, 2011, at 6:27 AM, David Knepper wrote:

> I am still hunting for the problem with my 270 - not 260- which was my mistake.
> 
> I have received many suggestions/tips and they are all most appreciated.
> 
> I will report what I find in a few days.  My 270 has worked flawlessly but all of a sudden the RX1 scale will not zero when the leads are "shorted."  The needle sits on half scale with little movement when I turn the zeroing pot on the front panel.
> 
> Replaced battery with a new EverReady and tested all the resistors with another meter.  This unit even smells new with absolutely no corrosion on the battery terminals.  It had all the indications of a weak battery but that is not the problem.
> 
> Now that I have a schematic I can begin to really troubleshoot the meter.

My 270 model 4 had a similar symptom on the Rx100 scale. It turned out to be R18, which instead of 123.57 ohms measured out at a few tens of kilo-ohms. So the previous owner must have smoked it, but the resistor didn't open, just went way high in value.

I'd suspect R17, which is supposed to be 1.109K ohms. It's probably smoked and gone high in value.

Note that the 270 model 5 has slightly different resistor values; do you have the correct manual for your version of the 270? The model 4 manual and earlier can be downloaded from Simpson260.com and the model 5 manual can be downloaded from SimpsonElectric.com

Best regards,
-Steve

-- 
Steve Byan <stevebyan at me.com>
Littleton, MA 01460