Cambridge CPT 505 Variometer

[John Foster]

I'm in the process of building a new instrument panel in my glider and am at the point of hooking it all back up. When I have the power cable plugged in to the back of the CAI CPT 505 and turn the power on, the needle deflects to -10kt, and if I switch it to 2x, then the needle deflects to -5kt. None of the air hoses are connected to the back of the instrument, so it is all open to the ambient air. I wouldn't think that would make a difference though. Is there something else I need to do, or is the instrument broken? I don't have a manual for it, and haven't been able to find one online. Thanks.

[Nick Kennedy[_3_]]

John
Buy yourself a early Christmas present and buy a LXNav S3 or S7.
Craggy will send you one tomorrow.

[John Foster]

On Thursday, July 18, 2019 at 8:32:04 PM UTC-6, Nick Kennedy wrote:
> John
> Buy yourself a early Christmas present and buy a LXNav S3 or S7.
> Craggy will send you one tomorrow.

Maybe next season. My budget is already overspent on this redo, and I barely have money for a tow right now! I'd like to make this one work until I can afford to replace it. Any help in this regard would be appreciated. Thanks.

[Steve Leonard[_2_]]

Is it maybe a CPT50S?

This might help. http://www.bas.uk.net/docs/Mk4_Vario.pdf

This says it will go full scale and stay there up to 3-5 minutes on initial powerup. Have you waited that long to see if it will come back to zero? Worth a try.

More manuals here. http://www.bas.uk.net/manuals.html

Best of luck with the vario!

Steve Leonard

[John Foster]

On Friday, July 19, 2019 at 10:30:22 AM UTC-6, Steve Leonard wrote:
> Is it maybe a CPT50S?
>
> This might help. http://www.bas.uk.net/docs/Mk4_Vario.pdf
>
> This says it will go full scale and stay there up to 3-5 minutes on initial powerup. Have you waited that long to see if it will come back to zero? Worth a try.
>
> More manuals here. http://www.bas.uk.net/manuals.html
>
> Best of luck with the vario!
>
> Steve Leonard

It could very well be a CPT50S. I'll need to look more closely next time. I have not tried leaving the power on for 3-5 min, and will do that next time. Thanks.

[John Foster]

On Friday, July 19, 2019 at 12:48:16 PM UTC-6, John Foster wrote:
> On Friday, July 19, 2019 at 10:30:22 AM UTC-6, Steve Leonard wrote:
> > Is it maybe a CPT50S?
> >
> > This might help. http://www.bas.uk.net/docs/Mk4_Vario.pdf
> >
> > This says it will go full scale and stay there up to 3-5 minutes on initial powerup. Have you waited that long to see if it will come back to zero? Worth a try.
> >
> > More manuals here. http://www.bas.uk.net/manuals.html
> >
> > Best of luck with the vario!
> >
> > Steve Leonard
>
> It could very well be a CPT50S. I'll need to look more closely next time.. I have not tried leaving the power on for 3-5 min, and will do that next time. Thanks.

It is indeed a CPT50S variometer. I tolerated on and waited. Immediately the needle deflected downwards for about a minute, then deflected upwards, and then started alternating back and forth from full downward deflection to full upward deflection at varying speeds. He did this for about 15 minutes before I turned the power back off. It did not seem to center itself. There are no other instruments or accessories plugged into the back of this variometer. Not sure what is going on.

[[email protected]]

On Thursday, July 18, 2019 at 8:32:04 PM UTC-6, Nick Kennedy wrote:
> John
> Buy yourself a early Christmas present and buy a LXNav S3 or S7.
> Craggy will send you one tomorrow.

John. I have a v7/S7 in like New condition if you are interested. Fair price. Email me if you are interested.

[John Foster]

On Saturday, July 20, 2019 at 7:22:32 AM UTC-6, wrote:
> On Thursday, July 18, 2019 at 8:32:04 PM UTC-6, Nick Kennedy wrote:
> > John
> > Buy yourself a early Christmas present and buy a LXNav S3 or S7.
> > Craggy will send you one tomorrow.
>
> John. I have a v7/S7 in like New condition if you are interested. Fair price. Email me if you are interested.

My dad, who is really smart with electronics, thought that it may be a capacitor problem, as the instrument has not been used in over 20yrs probably. He decided to try to "heal" the capacitors by applying a lower voltage to the instrument and gradually increasing it over time. We started at about 8 or 9 volts (don't remember exactly) and gradually increased the voltage in increments of 1.5 V over the course of the next 2-3 days, maxing out at 17.5 V. The instrument is rated to 18V at 300mA. He made sure the power supply was set to not deliver more than 250mA just in case. After the treatment, the vario will still have a full negative and positive deflection when powered up, for about a minute or two, and then settles down around the zero mark. I haven't gotten to test it out in flight yet, but this seems promising.

[john firth]

On Thursday, July 18, 2019 at 12:37:49 PM UTC-4, John Foster wrote:
> I'm in the process of building a new instrument panel in my glider and am at the point of hooking it all back up. When I have the power cable plugged in to the back of the CAI CPT 505 and turn the power on, the needle deflects to -10kt, and if I switch it to 2x, then the needle deflects to -5kt. None of the air hoses are connected to the back of the instrument, so it is all open to the ambient air. I wouldn't think that would make a difference though. Is there something else I need to do, or is the instrument broken? I don't have a manual for it, and haven't been able to find one online.. Thanks.

The CPT50S used a pressure transducer differentiated output; the DC part
is blocked by a 4 MF cap with a 20meg feedback; time constant 80sec
more than 10 mins is needed to settle to a usable value.
This was unacceptable and the design was dropped.
The CPT 50 was very susceptible to RF .( radio transmit)
JMF